Lock document in Tx() ctor (part of #2430)

This already fixes a lot of possible problems that can happen when a
script is running and modifying some part of a sprite that is being
backed up in a background thread.

We still need some work to being able to lock a sprite two or more
times in the same thread to write it. E.g. an app.transaction() should
lock the sprite for write access, but the script transaction function
could call a command, and that command could use a ContextWriter to
lock the sprite again. At the moment this is not possible because we
need a re-entrant RWLock implementation.

src/app/commands/cmd_add_color.cpp

@@ -130,7 +130,7 @@ void AddColorCommand::onExecute(Context* ctx)
     if (document) {
       frame_t frame = writer.frame();
 
-      Tx tx(writer.context(), friendlyName(), ModifyDocument);
+      Tx tx(writer, friendlyName(), ModifyDocument);
       tx(new cmd::SetPalette(sprite, frame, newPalette.get()));
       tx.commit();
     }

src/app/commands/cmd_background_from_layer.cpp

@@ -55,7 +55,7 @@ void BackgroundFromLayerCommand::onExecute(Context* context)
   Doc* document(writer.document());
 
   {
-    Tx tx(writer.context(), friendlyName());
+    Tx tx(writer, friendlyName());
     tx(new cmd::BackgroundFromLayer(static_cast<LayerImage*>(writer.layer())));
     tx.commit();
   }

src/app/commands/cmd_canvas_size.cpp

@@ -385,7 +385,7 @@ void CanvasSizeCommand::onExecute(Context* context)
     ContextWriter writer(reader);
     Doc* doc = writer.document();
     Sprite* sprite = writer.sprite();
-    Tx tx(writer.context(), "Canvas Size");
+    Tx tx(writer, "Canvas Size");
     DocApi api = doc->getApi(tx);
     api.cropSprite(sprite, bounds, params.trimOutside());
     tx.commit();

src/app/commands/cmd_cel_opacity.cpp

@@ -73,7 +73,7 @@ void CelOpacityCommand::onExecute(Context* context)
     return;
 
   {
-    Tx tx(writer.context(), "Set Cel Opacity");
+    Tx tx(writer, "Set Cel Opacity");
 
     // TODO the range of selected cels should be in app::Site.
     DocRange range;

src/app/commands/cmd_cel_properties.cpp

@@ -218,7 +218,7 @@ private:
                                  newUserData != m_cel->data()->userData()))) {
       try {
         ContextWriter writer(UIContext::instance());
-        Tx tx(writer.context(), "Set Cel Properties");
+        Tx tx(writer, "Set Cel Properties");
 
         DocRange range;
         if (m_range.enabled()) {

src/app/commands/cmd_clear_cel.cpp

@@ -48,7 +48,7 @@ void ClearCelCommand::onExecute(Context* context)
   Doc* document(writer.document());
   bool nonEditableLayers = false;
   {
-    Tx tx(writer.context(), "Clear Cel");
+    Tx tx(writer, "Clear Cel");
 
     const Site* site = writer.site();
     if (site->inTimeline() &&

src/app/commands/cmd_crop.cpp

@@ -72,7 +72,7 @@ void CropSpriteCommand::onExecute(Context* context)
     bounds = m_bounds;
 
   {
-    Tx tx(writer.context(), "Sprite Crop");
+    Tx tx(writer, "Sprite Crop");
     document->getApi(tx).cropSprite(sprite, bounds);
     tx.commit();
   }
@@ -119,7 +119,7 @@ void AutocropSpriteCommand::onExecute(Context* context)
   Doc* document(writer.document());
   Sprite* sprite(writer.sprite());
   {
-    Tx tx(writer.context(), onGetFriendlyName());
+    Tx tx(writer, onGetFriendlyName());
     document->getApi(tx).trimSprite(sprite, m_byGrid);
     tx.commit();
   }

src/app/commands/cmd_deselect_mask.cpp

@@ -44,7 +44,7 @@ void DeselectMaskCommand::onExecute(Context* context)
   ContextWriter writer(context);
   Doc* document(writer.document());
   {
-    Tx tx(writer.context(), "Deselect", DoesntModifyDocument);
+    Tx tx(writer, "Deselect", DoesntModifyDocument);
     tx(new cmd::DeselectMask(document));
     tx.commit();
   }

src/app/commands/cmd_duplicate_layer.cpp

@@ -49,7 +49,7 @@ void DuplicateLayerCommand::onExecute(Context* context)
   Doc* document = writer.document();
 
   {
-    Tx tx(writer.context(), "Layer Duplication");
+    Tx tx(writer, "Layer Duplication");
     LayerImage* sourceLayer = static_cast<LayerImage*>(writer.layer());
     DocApi api = document->getApi(tx);
     api.duplicateLayerAfter(sourceLayer,

src/app/commands/cmd_fill_and_stroke.cpp

@@ -81,7 +81,7 @@ void FillCommand::onExecute(Context* ctx)
     color = color_utils::color_for_layer(pref.colorBar.fgColor(), layer);
 
   {
-    Tx tx(writer.context(), "Fill Selection with Foreground Color");
+    Tx tx(writer, "Fill Selection with Foreground Color");
     {
       ExpandCelCanvas expand(
         site, layer,

src/app/commands/cmd_flatten_layers.cpp

@@ -57,7 +57,7 @@ void FlattenLayersCommand::onExecute(Context* context)
   ContextWriter writer(context);
   Sprite* sprite = writer.sprite();
   {
-    Tx tx(writer.context(), "Flatten Layers");
+    Tx tx(writer, "Flatten Layers");
 
     // TODO the range of selected layers should be in app::Site.
     DocRange range;

src/app/commands/cmd_flip.cpp

@@ -120,7 +120,7 @@ void FlipCommand::onExecute(Context* ctx)
   ContextWriter writer(ctx);
   Doc* document = writer.document();
   Sprite* sprite = writer.sprite();
-  Tx tx(ctx, friendlyName());
+  Tx tx(writer, friendlyName());
   DocApi api = document->getApi(tx);
 
   Mask* mask = document->mask();

src/app/commands/cmd_frame_properties.cpp

@@ -127,7 +127,7 @@ void FramePropertiesCommand::onExecute(Context* context)
     int newMsecs = window.frlen()->textInt();
 
     ContextWriter writer(reader);
-    Tx tx(writer.context(), "Frame Duration");
+    Tx tx(writer, "Frame Duration");
     DocApi api = writer.document()->getApi(tx);
 
     for (frame_t frame : selFrames)

src/app/commands/cmd_frame_tag_properties.cpp

@@ -91,7 +91,7 @@ void FrameTagPropertiesCommand::onExecute(Context* context)
     return;
 
   ContextWriter writer(reader);
-  Tx tx(writer.context(), friendlyName());
+  Tx tx(writer, friendlyName());
   Tag* tag = const_cast<Tag*>(foundTag);
 
   std::string name = window.nameValue();

src/app/commands/cmd_grid.cpp

@@ -73,7 +73,7 @@ protected:
     const Mask* mask = doc->mask();
     gfx::Rect newGrid = mask->bounds();
 
-    Tx tx(writer.context(), friendlyName(), ModifyDocument);
+    Tx tx(writer, friendlyName(), ModifyDocument);
     tx(new cmd::SetGridBounds(writer.sprite(), newGrid));
     tx.commit();
 
@@ -125,7 +125,7 @@ void GridSettingsCommand::onExecute(Context* context)
     bounds.h = std::max(bounds.h, 1);
 
     ContextWriter writer(context);
-    Tx tx(context, friendlyName(), ModifyDocument);
+    Tx tx(writer, friendlyName(), ModifyDocument);
     tx(new cmd::SetGridBounds(site.sprite(), bounds));
     tx.commit();
 

src/app/commands/cmd_import_sprite_sheet.cpp

@@ -512,8 +512,9 @@ void ImportSpriteSheetCommand::onExecute(Context* context)
     // The following steps modify the sprite, so we wrap all
     // operations in a undo-transaction.
     ContextWriter writer(context);
-    Tx tx(
-      writer.context(), Strings::import_sprite_sheet_title(), ModifyDocument);
+    Tx tx(writer,
+          Strings::import_sprite_sheet_title(),
+          ModifyDocument);
     DocApi api = document->getApi(tx);
 
     // Add the layer in the sprite.

src/app/commands/cmd_invert_mask.cpp

@@ -93,7 +93,7 @@ void InvertMaskCommand::onExecute(Context* context)
     mask->intersect(sprite->bounds());
 
     // Set the new mask
-    Tx tx(writer.context(), "Mask Invert", DoesntModifyDocument);
+    Tx tx(writer, "Mask Invert", DoesntModifyDocument);
     tx(new cmd::SetMask(document, mask.get()));
     tx.commit();
 

src/app/commands/cmd_layer_from_background.cpp

@@ -51,7 +51,7 @@ void LayerFromBackgroundCommand::onExecute(Context* context)
   ContextWriter writer(context);
   Doc* document(writer.document());
   {
-    Tx tx(writer.context(), friendlyName());
+    Tx tx(writer, friendlyName());
     tx(new cmd::LayerFromBackground(writer.layer()));
     tx.commit();
   }

src/app/commands/cmd_layer_opacity.cpp

@@ -69,7 +69,7 @@ void LayerOpacityCommand::onExecute(Context* context)
     return;
 
   {
-    Tx tx(writer.context(), "Set Layer Opacity");
+    Tx tx(writer, "Set Layer Opacity");
 
     // TODO the range of selected frames should be in app::Site.
     SelectedLayers selLayers;

src/app/commands/cmd_layer_properties.cpp

@@ -265,7 +265,7 @@ private:
                                      newBlendMode != static_cast<LayerImage*>(m_layer)->blendMode()))))) {
       try {
         ContextWriter writer(UIContext::instance());
-        Tx tx(writer.context(), "Set Layer Properties");
+        Tx tx(writer, "Set Layer Properties");
 
         DocRange range;
         if (m_range.enabled())
@@ -395,7 +395,7 @@ private:
           tileset->matchFlags() != tilesetInfo.matchFlags ||
           tilesetInfo.tsi != tilemap->tilesetIndex()) {
         ContextWriter writer(UIContext::instance());
-        Tx tx(writer.context(), "Set Tileset Properties");
+        Tx tx(writer, "Set Tileset Properties");
         // User changed tilemap's tileset
         if (tilesetInfo.tsi != tilemap->tilesetIndex()) {
           tileset = tilemap->sprite()->tilesets()->get(tilesetInfo.tsi);

src/app/commands/cmd_link_cels.cpp

@@ -57,7 +57,7 @@ void LinkCelsCommand::onExecute(Context* context)
     if (!site.inTimeline())
       return;
 
-    Tx tx(writer.context(), friendlyName());
+    Tx tx(writer, friendlyName());
 
     for (Layer* layer : site.selectedLayers()) {
       if (!layer->isImage())

src/app/commands/cmd_load_mask.cpp

@@ -77,7 +77,7 @@ void LoadMaskCommand::onExecute(Context* context)
   {
     ContextWriter writer(reader);
     Doc* document = writer.document();
-    Tx tx(writer.context(),
+    Tx tx(writer,
           Strings::load_selection_title(),
           DoesntModifyDocument);
     tx(new cmd::SetMask(document, mask.get()));

src/app/commands/cmd_mask_all.cpp

@@ -49,7 +49,7 @@ void MaskAllCommand::onExecute(Context* context)
   Mask newMask;
   newMask.replace(sprite->bounds());
 
-  Tx tx(writer.context(), "Select All", DoesntModifyDocument);
+  Tx tx(writer, "Select All", DoesntModifyDocument);
   tx(new cmd::SetMask(document, &newMask));
   document->resetTransformation();
   tx.commit();

src/app/commands/cmd_mask_by_color.cpp

@@ -187,7 +187,7 @@ void MaskByColorCommand::onExecute(Context* context)
   Doc* document(writer.document());
 
   if (apply) {
-    Tx tx(writer.context(), "Mask by Color", DoesntModifyDocument);
+    Tx tx(writer, "Mask by Color", DoesntModifyDocument);
     std::unique_ptr<Mask> mask(generateMask(*document->mask(),
                                             sprite, image, xpos, ypos,
                                             m_selMode->selectionMode()));

src/app/commands/cmd_mask_content.cpp

@@ -81,7 +81,7 @@ void MaskContentCommand::onExecute(Context* context)
       newMask.replace(cel->bounds());
     }
 
-    Tx tx(writer.context(), "Select Content", DoesntModifyDocument);
+    Tx tx(writer, "Select Content", DoesntModifyDocument);
     tx(new cmd::SetMask(document, &newMask));
     document->resetTransformation();
     tx.commit();

src/app/commands/cmd_merge_down_layer.cpp

@@ -79,7 +79,7 @@ void MergeDownLayerCommand::onExecute(Context* context)
   LayerImage* src_layer = static_cast<LayerImage*>(writer.layer());
   Layer* dst_layer = src_layer->getPrevious();
 
-  Tx tx(writer.context(), friendlyName(), ModifyDocument);
+  Tx tx(writer, friendlyName(), ModifyDocument);
 
   for (frame_t frpos = 0; frpos<sprite->totalFrames(); ++frpos) {
     // Get frames

src/app/commands/cmd_modify_selection.cpp

@@ -138,7 +138,7 @@ void ModifySelectionCommand::onExecute(Context* context)
   }
 
   // Set the new mask
-  Tx tx(writer.context(),
+  Tx tx(writer,
         friendlyName(),
         DoesntModifyDocument);
   tx(new cmd::SetMask(document, mask.get()));

src/app/commands/cmd_move_mask.cpp

@@ -87,7 +87,7 @@ void MoveMaskCommand::onExecute(Context* context)
       ContextWriter writer(context);
       Doc* document(writer.document());
       {
-        Tx tx(writer.context(), "Move Selection", DoesntModifyDocument);
+        Tx tx(writer, "Move Selection", DoesntModifyDocument);
         gfx::Point pt = document->mask()->bounds().origin();
         document->getApi(tx).setMaskPosition(pt.x+delta.x, pt.y+delta.y);
         tx.commit();
@@ -102,7 +102,7 @@ void MoveMaskCommand::onExecute(Context* context)
         ContextWriter writer(context);
         if (writer.cel()) {
           // Rotate content
-          Tx tx(writer.context(), "Shift Pixels");
+          Tx tx(writer, "Shift Pixels");
           tx(new cmd::ShiftMaskedCel(writer.cel(), delta.x, delta.y));
           tx.commit();
         }

src/app/commands/cmd_new_brush.cpp

@@ -117,7 +117,7 @@ void NewBrushCommand::onQuickboxEnd(Editor* editor, const gfx::Rect& rect, ui::M
       if (writer.cel()) {
         gfx::Rect canvasRect = (rect & writer.cel()->bounds());
         if (!canvasRect.isEmpty()) {
-          Tx tx(writer.context(), "Clear");
+          Tx tx(writer, "Clear");
           tx(new cmd::ClearRect(writer.cel(), canvasRect));
           tx.commit();
         }

src/app/commands/cmd_new_frame.cpp

@@ -102,7 +102,7 @@ void NewFrameCommand::onExecute(Context* context)
 #endif
 
   {
-    Tx tx(writer.context(), friendlyName());
+    Tx tx(writer, friendlyName());
     DocApi api = document->getApi(tx);
 
     switch (m_content) {

src/app/commands/cmd_new_frame_tag.cpp

@@ -74,7 +74,7 @@ void NewFrameTagCommand::onExecute(Context* context)
 
   {
     ContextWriter writer(reader);
-    Tx tx(writer.context(), friendlyName());
+    Tx tx(writer, friendlyName());
     tx(new cmd::AddTag(writer.sprite(), tag.get()));
     tag.release();
     tx.commit();

src/app/commands/cmd_new_layer.cpp

@@ -274,9 +274,8 @@ void NewLayerCommand::onExecute(Context* context)
 
   Layer* layer = nullptr;
   {
-    Tx tx(
-      writer.context(),
-      fmt::format(Strings::commands_NewLayer(), layerPrefix()));
+    Tx tx(writer,
+          fmt::format(Strings::commands_NewLayer(), layerPrefix()));
     DocApi api = document->getApi(tx);
     bool afterBackground = false;
 
@@ -428,7 +427,7 @@ void NewLayerCommand::onExecute(Context* context)
 #ifdef ENABLE_UI
     // Paste new layer from clipboard
     else if (params().fromClipboard() && layer->isImage()) {
-      context->clipboard()->paste(context, false);
+      context->clipboard()->paste(writer, false);
 
       if (layer->isReference()) {
         if (Cel* cel = layer->cel(site.frame())) {

src/app/commands/cmd_options.cpp

@@ -782,7 +782,7 @@ public:
         m_context->activeDocument()->sprite() &&
         m_context->activeDocument()->sprite()->gridBounds() != gridBounds()) {
       ContextWriter writer(m_context);
-      Tx tx(m_context, Strings::commands_GridSettings(), ModifyDocument);
+      Tx tx(writer, Strings::commands_GridSettings(), ModifyDocument);
       tx(new cmd::SetGridBounds(writer.sprite(), gridBounds()));
       tx.commit();
     }

src/app/commands/cmd_palette_size.cpp

@@ -78,7 +78,7 @@ void PaletteSizeCommand::onExecute(Context* context)
   palette.resize(std::clamp(ncolors, 1, std::numeric_limits<int>::max()));
 
   ContextWriter writer(reader);
-  Tx tx(context, "Palette Size", ModifyDocument);
+  Tx tx(writer, "Palette Size", ModifyDocument);
   tx(new cmd::SetPalette(writer.sprite(), frame, &palette));
   tx.commit();
 }

src/app/commands/cmd_remove_frame.cpp

@@ -53,7 +53,7 @@ void RemoveFrameCommand::onExecute(Context* context)
   Doc* document(writer.document());
   Sprite* sprite(writer.sprite());
   {
-    Tx tx(writer.context(), "Remove Frame");
+    Tx tx(writer, "Remove Frame");
     DocApi api = document->getApi(tx);
     const Site* site = writer.site();
     if (site->inTimeline() &&

src/app/commands/cmd_remove_frame_tag.cpp

@@ -77,7 +77,7 @@ void RemoveFrameTagCommand::onExecute(Context* context)
   if (!foundTag)
     return;
 
-  Tx tx(writer.context(), friendlyName());
+  Tx tx(writer, friendlyName());
   tx(new cmd::RemoveTag(sprite, foundTag));
   tx.commit();
 

src/app/commands/cmd_remove_layer.cpp

@@ -139,7 +139,7 @@ void RemoveLayerCommand::onExecute(Context* context)
   Doc* document(writer.document());
   Sprite* sprite(writer.sprite());
   {
-    Tx tx(writer.context(), "Remove Layer");
+    Tx tx(writer, "Remove Layer");
     DocApi api = document->getApi(tx);
     // We need to remove all the tilesets after the tilemaps are deleted
     // and in descending tileset index order, otherwise the tileset indexes

src/app/commands/cmd_remove_slice.cpp

@@ -101,7 +101,7 @@ void RemoveSliceCommand::onExecute(Context* context)
     ContextWriter writer(reader);
     Doc* document(writer.document());
     Sprite* sprite(writer.sprite());
-    Tx tx(writer.context(), "Remove Slice");
+    Tx tx(writer, "Remove Slice");
 
     for (auto slice : slicesToDelete.iterateAs<Slice>()) {
       ASSERT(slice);

src/app/commands/cmd_reselect_mask.cpp

@@ -53,7 +53,7 @@ void ReselectMaskCommand::onExecute(Context* context)
   ContextWriter writer(context);
   Doc* document(writer.document());
   {
-    Tx tx(writer.context(), "Reselect", DoesntModifyDocument);
+    Tx tx(writer, "Reselect", DoesntModifyDocument);
     tx(new cmd::ReselectMask(document));
     tx.commit();
   }

src/app/commands/cmd_select_tile.cpp

@@ -101,7 +101,7 @@ void SelectTileCommand::onExecute(Context* ctx)
   }
 
   // Set the new mask
-  Tx tx(writer.context(),
+  Tx tx(writer,
         friendlyName(),
         DoesntModifyDocument);
   tx(new cmd::SetMask(doc, mask.get()));

src/app/commands/cmd_set_loop_section.cpp

@@ -107,14 +107,14 @@ void SetLoopSectionCommand::onExecute(Context* ctx)
       loopTag = create_loop_tag(begin, end);
 
       ContextWriter writer(ctx);
-      Tx tx(writer.context(), "Add Loop");
+      Tx tx(writer, "Add Loop");
       tx(new cmd::AddTag(sprite, loopTag));
       tx.commit();
     }
     else if (loopTag->fromFrame() != begin ||
              loopTag->toFrame() != end) {
       ContextWriter writer(ctx);
-      Tx tx(writer.context(), "Set Loop Range");
+      Tx tx(writer, "Set Loop Range");
       tx(new cmd::SetTagRange(loopTag, begin, end));
       tx.commit();
     }
@@ -126,7 +126,7 @@ void SetLoopSectionCommand::onExecute(Context* ctx)
   else {
     if (loopTag) {
       ContextWriter writer(ctx);
-      Tx tx(writer.context(), "Remove Loop");
+      Tx tx(writer, "Remove Loop");
       tx(new cmd::RemoveTag(sprite, loopTag));
       tx.commit();
     }

src/app/commands/cmd_set_palette.cpp

@@ -37,7 +37,7 @@ void SetPaletteCommand::onExecute(Context* context)
 
   ContextWriter writer(context);
   if (writer.document()) {
-    Tx tx(writer.context(), "Set Palette");
+    Tx tx(writer, "Set Palette");
     writer.document()->getApi(tx)
       .setPalette(writer.sprite(), writer.frame(), m_palette);
     tx.commit();

src/app/commands/cmd_slice_properties.cpp

@@ -91,7 +91,7 @@ void SlicePropertiesCommand::onExecute(Context* context)
   {
     const SliceWindow::Mods mods = window.modifiedFields();
     ContextWriter writer(reader);
-    Tx tx(writer.context(), "Slice Properties");
+    Tx tx(writer, "Slice Properties");
 
     for (Slice* slice : slices.iterateAs<Slice>()) {
       // Change name

src/app/commands/cmd_sprite_properties.cpp

@@ -96,10 +96,11 @@ public:
 private:
    void onDuplicate(const doc::Tileset* tileset)
    {
+     auto sprite = tileset->sprite();
      auto tilesetClone = Tileset::MakeCopyCopyingImages(tileset);
 
-     Tx tx(fmt::format(Strings::commands_TilesetDuplicate()));
-     tx(new cmd::AddTileset(tileset->sprite(), tilesetClone));
+     Tx tx(sprite, fmt::format(Strings::commands_TilesetDuplicate()));
+     tx(new cmd::AddTileset(sprite, tilesetClone));
      tx.commit();
 
      TilesetDuplicated(tilesetClone);
@@ -121,8 +122,9 @@ private:
       return;
     }
 
-    Tx tx(fmt::format(Strings::commands_TilesetDelete()));
-    tx(new cmd::RemoveTileset(tileset->sprite(), tsi));
+    auto sprite = tileset->sprite();
+    Tx tx(sprite, fmt::format(Strings::commands_TilesetDelete()));
+    tx(new cmd::RemoveTileset(sprite, tsi));
     tx.commit();
 
     TilesetDeleted(this);
@@ -351,7 +353,7 @@ void SpritePropertiesCommand::onExecute(Context* context)
 
         ContextWriter writer(context);
         Sprite* sprite(writer.sprite());
-        Tx tx(writer.context(), Strings::sprite_properties_assign_color_profile());
+        Tx tx(writer, Strings::sprite_properties_assign_color_profile());
         tx(new cmd::AssignColorProfile(
              sprite, colorSpaces[selectedColorProfile]->gfxColorSpace()));
         tx.commit();
@@ -364,7 +366,7 @@ void SpritePropertiesCommand::onExecute(Context* context)
 
         ContextWriter writer(context);
         Sprite* sprite(writer.sprite());
-        Tx tx(writer.context(), Strings::sprite_properties_convert_color_profile());
+        Tx tx(writer, Strings::sprite_properties_convert_color_profile());
         tx(new cmd::ConvertColorProfile(
              sprite, colorSpaces[selectedColorProfile]->gfxColorSpace()));
         tx.commit();
@@ -394,7 +396,7 @@ void SpritePropertiesCommand::onExecute(Context* context)
     if (index != sprite->transparentColor() ||
         pixelRatio != sprite->pixelRatio() ||
         newUserData != sprite->userData()) {
-      Tx tx(writer.context(), Strings::sprite_properties_change_sprite_props());
+      Tx tx(writer, Strings::sprite_properties_change_sprite_props());
       DocApi api = writer.document()->getApi(tx);
 
       if (index != sprite->transparentColor())

src/app/commands/cmd_unlink_cel.cpp

@@ -47,7 +47,7 @@ void UnlinkCelCommand::onExecute(Context* context)
   Doc* document(writer.document());
   bool nonEditableLayers = false;
   {
-    Tx tx(writer.context(), "Unlink Cel");
+    Tx tx(writer, "Unlink Cel");
 
     const Site* site = writer.site();
     if (site->inTimeline() &&

src/app/commands/convert_layer.cpp

@@ -180,7 +180,7 @@ void ConvertLayerCommand::onExecute(Context* ctx)
   ContextWriter writer(ctx);
   Doc* document(writer.document());
   {
-    Tx tx(ctx, friendlyName());
+    Tx tx(writer, friendlyName());
 
     switch (params().to()) {
 

src/app/commands/filters/filter_manager_impl.cpp

@@ -353,7 +353,7 @@ void FilterManagerImpl::initTransaction()
 {
   ASSERT(!m_tx);
   m_writer.reset(new ContextWriter(m_reader));
-  m_tx.reset(new Tx(m_writer->context(),
+  m_tx.reset(new Tx(*m_writer,
                     m_filter->getName(),
                     ModifyDocument));
 }

src/app/commands/move_colors_command.cpp

@@ -55,7 +55,7 @@ protected:
     if (!writer.palette())
       return;
 
-    Tx tx(writer.context(), friendlyName(), ModifyDocument);
+    Tx tx(writer, friendlyName(), ModifyDocument);
     const int beforeIndex = params().before();
     int currentEntry = picks.firstPick();
 

src/app/commands/move_tiles_command.cpp

@@ -57,7 +57,7 @@ protected:
     if (picks.picks() == 0)
       return;
 
-    Tx tx(writer.context(), onGetFriendlyName(), ModifyDocument);
+    Tx tx(writer, onGetFriendlyName(), ModifyDocument);
     const int beforeIndex = params().before();
     int currentEntry = picks.firstPick();
 

src/app/doc_api_tests.cpp

@@ -52,7 +52,7 @@ TEST_F(BasicDocApiTest, RestackLayerBefore)
 {
   EXPECT_EQ(layer1, root->firstLayer());
   {
-    Tx tx(&ctx, "");
+    Tx tx(sprite, "");
     // Do nothing
     doc->getApi(tx).restackLayerBefore(layer1, layer1->parent(), layer1);
     EXPECT_EQ(layer1, root->firstLayer());
@@ -63,7 +63,7 @@ TEST_F(BasicDocApiTest, RestackLayerBefore)
 
   EXPECT_EQ(layer1, root->firstLayer());
   {
-    Tx tx(&ctx, "");
+    Tx tx(sprite, "");
     doc->getApi(tx).restackLayerBefore(layer1, layer3->parent(), layer3);
     EXPECT_EQ(layer2, root->firstLayer());
     EXPECT_EQ(layer1, root->firstLayer()->getNext());
@@ -73,7 +73,7 @@ TEST_F(BasicDocApiTest, RestackLayerBefore)
 
   EXPECT_EQ(layer1, root->firstLayer());
   {
-    Tx tx(&ctx, "");
+    Tx tx(sprite, "");
     doc->getApi(tx).restackLayerBefore(layer1, layer1->parent(), nullptr);
     EXPECT_EQ(layer2, root->firstLayer());
     EXPECT_EQ(layer3, root->firstLayer()->getNext());
@@ -86,7 +86,7 @@ TEST_F(BasicDocApiTest, RestackLayerAfter)
 {
   EXPECT_EQ(layer1, root->firstLayer());
   {
-    Tx tx(&ctx, "");
+    Tx tx(sprite, "");
     // Do nothing
     doc->getApi(tx).restackLayerAfter(layer1, layer1->parent(), layer1);
     EXPECT_EQ(layer1, root->firstLayer());
@@ -97,7 +97,7 @@ TEST_F(BasicDocApiTest, RestackLayerAfter)
 
   EXPECT_EQ(layer1, root->firstLayer());
   {
-    Tx tx(&ctx, "");
+    Tx tx(sprite, "");
     doc->getApi(tx).restackLayerAfter(layer1, layer3->parent(), layer3);
     EXPECT_EQ(layer2, root->firstLayer());
     EXPECT_EQ(layer3, root->firstLayer()->getNext());
@@ -107,7 +107,7 @@ TEST_F(BasicDocApiTest, RestackLayerAfter)
 
   EXPECT_EQ(layer1, root->firstLayer());
   {
-    Tx tx(&ctx, "");
+    Tx tx(sprite, "");
     doc->getApi(tx).restackLayerAfter(layer3, layer3->parent(), nullptr);
     EXPECT_EQ(layer3, root->firstLayer());
     EXPECT_EQ(layer1, root->firstLayer()->getNext());
@@ -132,7 +132,7 @@ TEST_F(BasicDocApiTest, MoveCel)
   // Create a copy for later comparison.
   std::unique_ptr<Image> expectedImage(Image::createCopy(image1));
 
-  Tx tx(&ctx, "");
+  Tx tx(sprite, "");
   doc->getApi(tx).moveCel(
     layer1, frame_t(0),
     layer2, frame_t(1));

src/app/doc_range_ops.cpp

@@ -333,7 +333,7 @@ static DocRange drop_range_op(
     const app::Context* context = static_cast<app::Context*>(doc->context());
     const ContextReader reader(context);
     ContextWriter writer(reader);
-    Tx tx(writer.context(), undoLabel, ModifyDocument);
+    Tx tx(writer, undoLabel, ModifyDocument);
     DocApi api = doc->getApi(tx);
 
     // TODO Try to add the range with just one call to DocApi
@@ -490,7 +490,7 @@ void reverse_frames(Doc* doc, const DocRange& range)
   const app::Context* context = static_cast<app::Context*>(doc->context());
   const ContextReader reader(context);
   ContextWriter writer(reader);
-  Tx tx(writer.context(), "Reverse Frames");
+  Tx tx(writer, "Reverse Frames");
   DocApi api = doc->getApi(tx);
   Sprite* sprite = doc->sprite();
   LayerList layers;

src/app/script/app_object.cpp

@@ -13,6 +13,7 @@
 #include "app/commands/commands.h"
 #include "app/commands/params.h"
 #include "app/context.h"
+#include "app/context_access.h"
 #include "app/doc.h"
 #include "app/doc_access.h"
 #include "app/i18n/strings.h"
@@ -152,8 +153,22 @@ int App_transaction(lua_State* L)
   }
 
   if (lua_isfunction(L, index)) {
-    Tx tx(label); // Create a new transaction so it exists in the whole
-                  // duration of the argument function call.
+    app::Context* ctx = App::instance()->context();
+    if (!ctx)
+      return luaL_error(L, "no context");
+
+    // Create a new transaction so it exists in the whole duration of
+    // the argument function call.
+#if 0
+    // TODO To be able to lock the document in the transaction we have
+    // to create a re-entrant RWLock implementation to allow to call
+    // commands (creating sub-ContextWriters) inside the
+    // app.transaction()
+    ContextWriter writer(ctx);
+    Tx tx(writer, label);
+#else
+    Tx tx(Tx::DontLockDoc, ctx, ctx->activeDocument(), label);
+#endif
 
     lua_pushvalue(L, -1);
     if (lua_pcall(L, 0, LUA_MULTRET, 0) == LUA_OK)

src/app/script/cel_class.cpp

@@ -110,8 +110,8 @@ int Cel_set_frame(lua_State* L)
   if (cel->frame() == frame)
     return 0;
 
-  Tx tx;
   Doc* doc = static_cast<Doc*>(cel->document());
+  Tx tx(doc);
   DocApi api = doc->getApi(tx);
   api.moveCel(cel->layer(), cel->frame(),
               cel->layer(), frame);
@@ -125,7 +125,7 @@ int Cel_set_image(lua_State* L)
   auto srcImage = get_image_from_arg(L, 2);
   ImageRef newImage(Image::createCopy(srcImage));
 
-  Tx tx;
+  Tx tx(cel->sprite());
   tx(new cmd::ReplaceImage(cel->sprite(),
                            cel->imageRef(),
                            newImage));
@@ -137,7 +137,7 @@ int Cel_set_position(lua_State* L)
 {
   auto cel = get_docobj<Cel>(L, 1);
   const gfx::Point pos = convert_args_into_point(L, 2);
-  Tx tx;
+  Tx tx(cel->sprite());
   tx(new cmd::SetCelPosition(cel, pos.x, pos.y));
   tx.commit();
   return 0;
@@ -146,7 +146,7 @@ int Cel_set_position(lua_State* L)
 int Cel_set_opacity(lua_State* L)
 {
   auto cel = get_docobj<Cel>(L, 1);
-  Tx tx;
+  Tx tx(cel->sprite());
   tx(new cmd::SetCelOpacity(cel, lua_tointeger(L, 2)));
   tx.commit();
   return 0;
@@ -155,7 +155,7 @@ int Cel_set_opacity(lua_State* L)
 int Cel_set_zIndex(lua_State* L)
 {
   auto cel = get_docobj<Cel>(L, 1);
-  Tx tx;
+  Tx tx(cel->sprite());
   tx(new cmd::SetCelZIndex(cel, lua_tointeger(L, 2)));
   tx.commit();
   return 0;

src/app/script/frame_class.cpp

@@ -104,7 +104,7 @@ int Frame_set_duration(lua_State* L)
   auto obj = get_obj<FrameObj>(L, 1);
   auto sprite = obj->sprite(L);
   double duration = lua_tonumber(L, 2) * 1000.0;
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetFrameDuration(sprite, obj->frame, int(duration)));
   tx.commit();
   return 1;

src/app/script/image_class.cpp

@@ -311,14 +311,7 @@ int Image_drawImage(lua_State* L)
   Image* dst = obj->image(L);
   const Image* src = sprite->image(L);
 
-  // If the destination image is not related to a sprite, we just draw
-  // the source image without undo information.
-  if (obj->cel(L) == nullptr) {
-    doc::blend_image(dst, src,
-                     pos.x, pos.y,
-                     opacity, blendMode);
-  }
-  else {
+  if (auto cel = obj->cel(L)) {
     gfx::Rect bounds(0, 0, src->size().w, src->size().h);
     buf.reset(new doc::ImageBuffer);
     ImageRef tmp_src(
@@ -329,12 +322,19 @@ int Image_drawImage(lua_State* L)
     // TODO Use something similar to doc::algorithm::shrink_bounds2()
     //      but we need something that does the render and compares
     //      the minimal modified area.
-    Tx tx;
+    Tx tx(cel->sprite());
     tx(new cmd::CopyRegion(
          dst, tmp_src.get(), gfx::Region(bounds),
          gfx::Point(pos.x + bounds.x, pos.y + bounds.y)));
     tx.commit();
   }
+  // If the destination image is not related to a sprite, we just draw
+  // the source image without undo information.
+  else {
+    doc::blend_image(dst, src,
+                     pos.x, pos.y,
+                     opacity, blendMode);
+  }
   return 0;
 }
 
@@ -349,13 +349,8 @@ int Image_drawSprite(lua_State* L)
   ASSERT(dst);
   ASSERT(sprite);
 
-  // If the destination image is not related to a sprite, we just draw
-  // the source image without undo information.
-  if (obj->cel(L) == nullptr) {
-    render_sprite(dst, sprite, frame, pos.x, pos.y);
-  }
-  else {
-    Tx tx;
+  if (auto cel = obj->cel(L)) {
+    Tx tx(cel->sprite());
 
     ImageRef tmp(Image::createCopy(dst));
     render_sprite(tmp.get(), sprite, frame, pos.x, pos.y);
@@ -369,6 +364,11 @@ int Image_drawSprite(lua_State* L)
 
     tx.commit();
   }
+  // If the destination image is not related to a sprite, we just draw
+  // the source image without undo information.
+  else {
+    render_sprite(dst, sprite, frame, pos.x, pos.y);
+  }
   return 0;
 }
 
@@ -571,7 +571,7 @@ int Image_resize(lua_State* L)
   // If the destination image is not related to a sprite, we just draw
   // the source image without undo information.
   if (cel) {
-    Tx tx;
+    Tx tx(cel->sprite());
     resize_cel_image(tx, cel, scale, method,
                      gfx::PointF(pivot));
     tx.commit();
@@ -627,14 +627,14 @@ int Image_flip(lua_State* L)
   if (lua_isinteger(L, 2))
     flipType = (doc::algorithm::FlipType)lua_tointeger(L, 2);
 
-  if (obj->cel(L) == nullptr) {
-    doc::algorithm::flip_image(img, img->bounds(), flipType);
-  }
-  else {
-    Tx tx;
+  if (auto cel = obj->cel(L)) {
+    Tx tx(cel->sprite());
     tx(new cmd::FlipImage(img, img->bounds(), flipType));
     tx.commit();
   }
+  else {
+    doc::algorithm::flip_image(img, img->bounds(), flipType);
+  }
   return 0;
 }
 

src/app/script/layer_class.cpp

@@ -250,7 +250,7 @@ int Layer_set_name(lua_State* L)
   auto layer = get_docobj<Layer>(L, 1);
   const char* name = lua_tostring(L, 2);
   if (name) {
-    Tx tx;
+    Tx tx(layer->sprite());
     tx(new cmd::SetLayerName(layer, name));
     tx.commit();
   }
@@ -262,7 +262,7 @@ int Layer_set_opacity(lua_State* L)
   auto layer = get_docobj<Layer>(L, 1);
   const int opacity = lua_tointeger(L, 2);
   if (layer->isImage()) {
-    Tx tx;
+    Tx tx(layer->sprite());
     tx(new cmd::SetLayerOpacity(static_cast<LayerImage*>(layer), opacity));
     tx.commit();
   }
@@ -274,7 +274,7 @@ int Layer_set_blendMode(lua_State* L)
   auto layer = get_docobj<Layer>(L, 1);
   auto blendMode = app::script::BlendMode(lua_tointeger(L, 2));
   if (layer->isImage()) {
-    Tx tx;
+    Tx tx(layer->sprite());
     tx(new cmd::SetLayerBlendMode(static_cast<LayerImage*>(layer),
                                   base::convert_to<doc::BlendMode>(blendMode)));
     tx.commit();
@@ -313,7 +313,7 @@ int Layer_set_stackIndex(lua_State* L)
     return 0;
 
   Doc* doc = static_cast<Doc*>(layer->sprite()->document());
-  Tx tx;
+  Tx tx(doc);
   DocApi(doc, tx).restackLayerBefore(layer, parent, beforeThis);
   tx.commit();
   return 0;
@@ -381,7 +381,7 @@ int Layer_set_parent(lua_State* L)
 
   if (parent) {
     Doc* doc = static_cast<Doc*>(layer->sprite()->document());
-    Tx tx;
+    Tx tx(doc);
     DocApi(doc, tx).restackLayerAfter(
       layer, parent, parent->lastLayer());
     tx.commit();
@@ -402,7 +402,7 @@ int Layer_set_tileset(lua_State* L)
       tsi = lua_tointeger(L, 2);
 
     if (tsi != tilemap->tilesetIndex()) {
-      Tx tx;
+      Tx tx(layer->sprite());
       tx(new cmd::SetLayerTileset(tilemap, tsi));
       tx.commit();
     }

src/app/script/palette_class.cpp

@@ -165,7 +165,7 @@ int Palette_resize(lua_State* L)
     newPal.resize(ncolors);
 
     if (*pal != newPal) {
-      Tx tx;
+      Tx tx(sprite);
       tx(new cmd::SetPalette(sprite, pal->frame(), &newPal));
       tx.commit();
     }
@@ -212,7 +212,7 @@ int Palette_setColor(lua_State* L)
     Palette newPal(*pal);
     newPal.setEntry(i, docColor);
 
-    Tx tx;
+    Tx tx(sprite);
     tx(new cmd::SetPalette(sprite, pal->frame(), &newPal));
     tx.commit();
   }

src/app/script/properties_class.cpp

@@ -126,8 +126,8 @@ int Properties_newindex(lua_State* L)
 
   // TODO add Object::sprite() member function
   //if (obj->sprite()) {
-  if (App::instance()->context()->activeDocument()) {
-    Tx tx;
+  if (auto doc = App::instance()->context()->activeDocument()) {
+    Tx tx(doc);                 // TODO propObj might not be member of "doc"
     if (propObj->ti != doc::notile) {
       tx(new cmd::SetTileDataProperty(static_cast<doc::Tileset*>(obj),
                                       propObj->ti, propObj->extID, field,
@@ -165,8 +165,8 @@ int Properties_call(lua_State* L)
 
     // TODO add Object::sprite() member function
     //if (obj->sprite()) {
-    if (App::instance()->context()->activeDocument()) {
-      Tx tx;
+    if (auto doc = App::instance()->context()->activeDocument()) {
+      Tx tx(doc);                 // TODO propObj might not be member of "doc"
       if (propObj->ti != doc::notile) {
         tx(new cmd::SetTileDataProperties(static_cast<doc::Tileset*>(obj),
                                           propObj->ti, extID, std::move(newProperties)));

src/app/script/selection_class.cpp

@@ -117,7 +117,7 @@ int Selection_deselect(lua_State* L)
     ASSERT(doc);
 
     if (doc->isMaskVisible()) {
-      Tx tx;
+      Tx tx(doc);
       tx(new cmd::DeselectMask(doc));
       tx.commit();
     }
@@ -180,7 +180,7 @@ int Selection_op(lua_State* L, OpMask opMask, OpRect opRect)
       Mask newMask;
       opMask(newMask, *mask, *otherMask);
 
-      Tx tx;
+      Tx tx(sprite);
       tx(new cmd::SetMask(doc, &newMask));
       tx.commit();
     }
@@ -198,7 +198,7 @@ int Selection_op(lua_State* L, OpMask opMask, OpRect opRect)
       Mask newMask;
       opRect(newMask, *mask, bounds);
 
-      Tx tx;
+      Tx tx(sprite);
       tx(new cmd::SetMask(doc, &newMask));
       tx.commit();
     }
@@ -223,7 +223,7 @@ int Selection_selectAll(lua_State* L)
     Mask newMask;
     newMask.replace(sprite->bounds());
 
-    Tx tx;
+    Tx tx(doc);
     tx(new cmd::SetMask(doc, &newMask));
     tx.commit();
   }
@@ -290,7 +290,7 @@ int Selection_set_origin(lua_State* L)
   if (auto sprite = obj->sprite(L)) {
     Doc* doc = static_cast<Doc*>(sprite->document());
     if (doc->isMaskVisible()) {
-      Tx tx;
+      Tx tx(doc);
       doc->getApi(tx).setMaskPosition(pt.x, pt.y);
       tx.commit();
     }

src/app/script/slice_class.cpp

@@ -83,7 +83,7 @@ int Slice_set_name(lua_State* L)
   auto slice = get_docobj<Slice>(L, 1);
   const char* name = lua_tostring(L, 2);
   if (name) {
-    Tx tx;
+    Tx tx(slice->sprite());
     tx(new cmd::SetSliceName(slice, name));
     tx.commit();
   }
@@ -98,7 +98,7 @@ int Slice_set_bounds(lua_State* L)
   if (const SliceKey* srcKey = slice->getByFrame(0))
     key = *srcKey;
   key.setBounds(bounds);
-  Tx tx;
+  Tx tx(slice->sprite());
   tx(new cmd::SetSliceKey(slice, 0, key));
   tx.commit();
   return 0;
@@ -112,7 +112,7 @@ int Slice_set_center(lua_State* L)
   if (const SliceKey* srcKey = slice->getByFrame(0))
     key = *srcKey;
   key.setCenter(center);
-  Tx tx;
+  Tx tx(slice->sprite());
   tx(new cmd::SetSliceKey(slice, 0, key));
   tx.commit();
   return 0;
@@ -126,7 +126,7 @@ int Slice_set_pivot(lua_State* L)
   if (const SliceKey* srcKey = slice->getByFrame(0))
     key = *srcKey;
   key.setPivot(pivot);
-  Tx tx;
+  Tx tx(slice->sprite());
   tx(new cmd::SetSliceKey(slice, 0, key));
   tx.commit();
   return 0;

src/app/script/sprite_class.cpp

@@ -201,7 +201,7 @@ int Sprite_crop(lua_State* L)
   }
 
   if (!bounds.isEmpty()) {
-    Tx tx;
+    Tx tx(doc);
     DocApi(doc, tx).cropSprite(sprite, bounds);
     tx.commit();
   }
@@ -285,7 +285,7 @@ int Sprite_loadPalette(lua_State* L)
     Doc* doc = static_cast<Doc*>(sprite->document());
     std::unique_ptr<doc::Palette> palette(load_palette(absFn.c_str()));
     if (palette) {
-      Tx tx;
+      Tx tx(doc);
       // TODO Merge this with the code in LoadPaletteCommand
       doc->getApi(tx).setPalette(sprite, 0, palette.get());
       tx.commit();
@@ -301,7 +301,7 @@ int Sprite_setPalette(lua_State* L)
   if (sprite && pal) {
     Doc* doc = static_cast<Doc*>(sprite->document());
 
-    Tx tx;
+    Tx tx(doc);
     doc->getApi(tx).setPalette(sprite, 0, pal);
     tx.commit();
   }
@@ -312,7 +312,7 @@ int Sprite_assignColorSpace(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   auto cs = get_obj<gfx::ColorSpace>(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AssignColorProfile(
        sprite, base::make_ref<gfx::ColorSpace>(*cs)));
   tx.commit();
@@ -323,7 +323,7 @@ int Sprite_convertColorSpace(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   auto cs = get_obj<gfx::ColorSpace>(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::ConvertColorProfile(
        sprite, base::make_ref<gfx::ColorSpace>(*cs)));
   tx.commit();
@@ -338,7 +338,7 @@ int Sprite_flatten(lua_State* L)
   for (auto layer : sprite->root()->layers())
     range.selectLayer(layer);
 
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::FlattenLayers(sprite, range.selectedLayers(), true));
   tx.commit();
   return 0;
@@ -349,7 +349,7 @@ int Sprite_newLayer(lua_State* L)
   auto sprite = get_docobj<Sprite>(L, 1);
   doc::Layer* newLayer = new doc::LayerImage(sprite);
 
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AddLayer(sprite->root(), newLayer, sprite->root()->lastLayer()));
   tx.commit();
 
@@ -362,7 +362,7 @@ int Sprite_newGroup(lua_State* L)
   auto sprite = get_docobj<Sprite>(L, 1);
   doc::Layer* newGroup = new doc::LayerGroup(sprite);
 
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AddLayer(sprite->root(), newGroup, sprite->root()->lastLayer()));
   tx.commit();
 
@@ -388,7 +388,7 @@ int Sprite_deleteLayer(lua_State* L)
   if (layer) {
     if (sprite != layer->sprite())
       return luaL_error(L, "the layer doesn't belong to the sprite");
-    Tx tx;
+    Tx tx(sprite);
     tx(new cmd::RemoveLayer(layer));
     tx.commit();
     return 0;
@@ -412,7 +412,7 @@ int Sprite_newFrame(lua_State* L)
 
   Doc* doc = static_cast<Doc*>(sprite->document());
 
-  Tx tx;
+  Tx tx(doc);
   doc->getApi(tx).addFrame(sprite, copyThis);
   tx.commit();
 
@@ -432,7 +432,7 @@ int Sprite_newEmptyFrame(lua_State* L)
 
   Doc* doc = static_cast<Doc*>(sprite->document());
 
-  Tx tx;
+  Tx tx(doc);
   DocApi(doc, tx).addEmptyFrame(sprite, frame);
   tx.commit();
 
@@ -449,7 +449,7 @@ int Sprite_deleteFrame(lua_State* L)
 
   Doc* doc = static_cast<Doc*>(sprite->document());
 
-  Tx tx;
+  Tx tx(doc);
   doc->getApi(tx).removeFrame(sprite, frame);
   tx.commit();
   return 0;
@@ -479,7 +479,7 @@ int Sprite_newCel(lua_State* L)
     cel = layer->cel(frame);
     ASSERT(cel);
 
-    Tx tx;
+    Tx tx(doc);
     DocApi api = doc->getApi(tx);
     api.clearCel(layer, frame);
     if (srcImage) {
@@ -499,7 +499,7 @@ int Sprite_newCel(lua_State* L)
     cel = new Cel(frame, image);
     cel->setPosition(pos);
 
-    Tx tx;
+    Tx tx(doc);
     DocApi api = doc->getApi(tx);
     if (layer->cel(frame))
       api.clearCel(layer, frame);
@@ -526,7 +526,7 @@ int Sprite_deleteCel(lua_State* L)
   }
 
   if (cel) {
-    Tx tx;
+    Tx tx(sprite);
     tx(new cmd::ClearCel(cel));
     tx.commit();
     return 0;
@@ -543,7 +543,7 @@ int Sprite_newTag(lua_State* L)
   auto to = get_frame_number_from_arg(L, 3);
   auto tag = new doc::Tag(from, to);
 
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AddTag(sprite, tag));
   tx.commit();
 
@@ -563,7 +563,7 @@ int Sprite_deleteTag(lua_State* L)
   if (tag) {
     if (sprite != tag->owner()->sprite())
       return luaL_error(L, "the tag doesn't belong to the sprite");
-    Tx tx;
+    Tx tx(sprite);
     tx(new cmd::RemoveTag(sprite, tag));
     tx.commit();
     return 0;
@@ -582,7 +582,7 @@ int Sprite_newSlice(lua_State* L)
   if (!bounds.isEmpty())
     slice->insert(0, doc::SliceKey(bounds));
 
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AddSlice(sprite, slice));
   tx.commit();
 
@@ -602,7 +602,7 @@ int Sprite_deleteSlice(lua_State* L)
   if (slice) {
     if (sprite != slice->owner()->sprite())
       return luaL_error(L, "the slice doesn't belong to the sprite");
-    Tx tx;
+    Tx tx(sprite);
     tx(new cmd::RemoveSlice(sprite, slice));
     tx.commit();
     return 0;
@@ -663,7 +663,7 @@ int Sprite_newTileset(lua_State* L)
     tileset = new Tileset(sprite, grid, ntiles);
   }
 
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AddTileset(sprite, tileset));
   tx.commit();
 
@@ -686,7 +686,7 @@ int Sprite_deleteTileset(lua_State* L)
   if (tileset && tsi >= 0) {
     if (sprite != tileset->sprite())
       return luaL_error(L, "the tileset doesn't belong to the sprite");
-    Tx tx;
+    Tx tx(sprite);
 
     // Set the tileset from all layers that are using it
     for (auto layer : sprite->allLayers()) {
@@ -725,7 +725,7 @@ int Sprite_newTile(lua_State* L)
       return luaL_error(L, "index must be equal to or greater than 1");
   }
   ts->insert(ti, ts->makeEmptyTile());
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::AddTile(ts, ti));
   tx.commit();
   push_tile(L, ts, ti);
@@ -749,7 +749,7 @@ int Sprite_deleteTile(lua_State* L)
     return luaL_error(L, "tile index = 0 cannot be removed");
   if (ti < 0 || ti >= ts->size())
     return luaL_error(L, "index out of bounds");
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::RemoveTile(ts, ti));
   tx.commit();
   push_tile(L, ts, ti);
@@ -902,7 +902,7 @@ int Sprite_set_transparentColor(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   const int index = lua_tointeger(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetTransparentColor(sprite, index));
   tx.commit();
   return 0;
@@ -920,7 +920,7 @@ int Sprite_set_width(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   const int width = lua_tointeger(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetSpriteSize(sprite, width, sprite->height()));
   tx.commit();
   return 0;
@@ -930,7 +930,7 @@ int Sprite_set_height(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   const int height = lua_tointeger(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetSpriteSize(sprite, sprite->width(), height));
   tx.commit();
   return 0;
@@ -941,7 +941,7 @@ int Sprite_set_selection(lua_State* L)
   auto sprite = get_docobj<Sprite>(L, 1);
   const auto mask = get_mask_from_arg(L, 2);
   Doc* doc = static_cast<Doc*>(sprite->document());
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetMask(doc, mask));
   tx.commit();
   return 0;
@@ -965,7 +965,7 @@ int Sprite_set_gridBounds(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   const gfx::Rect bounds = convert_args_into_rect(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetGridBounds(sprite, bounds));
   tx.commit();
   return 0;
@@ -982,7 +982,7 @@ int Sprite_set_pixelRatio(lua_State* L)
 {
   auto sprite = get_docobj<Sprite>(L, 1);
   const gfx::Size pixelRatio = convert_args_into_size(L, 2);
-  Tx tx;
+  Tx tx(sprite);
   tx(new cmd::SetPixelRatio(sprite, pixelRatio));
   tx.commit();
   return 0;
@@ -1006,7 +1006,7 @@ int Sprite_set_tileManagementPlugin(lua_State* L)
     value = p;
 
   if (sprite->tileManagementPlugin() != value) {
-    Tx tx;
+    Tx tx(sprite);
     tx(new cmd::SetSpriteTileManagementPlugin(sprite, value));
     tx.commit();
   }

src/app/script/tag_class.cpp

@@ -96,7 +96,7 @@ int Tag_set_fromFrame(lua_State* L)
 {
   auto tag = get_docobj<Tag>(L, 1);
   const auto fromFrame = get_frame_number_from_arg(L, 2);
-  Tx tx;
+  Tx tx(tag->sprite());
   tx(new cmd::SetTagRange(tag, fromFrame,
                           std::max(fromFrame, tag->toFrame())));
   tx.commit();
@@ -107,7 +107,7 @@ int Tag_set_toFrame(lua_State* L)
 {
   auto tag = get_docobj<Tag>(L, 1);
   const auto toFrame = get_frame_number_from_arg(L, 2);
-  Tx tx;
+  Tx tx(tag->sprite());
   tx(new cmd::SetTagRange(tag,
                                std::min(tag->fromFrame(), toFrame),
                                toFrame));
@@ -120,7 +120,7 @@ int Tag_set_name(lua_State* L)
   auto tag = get_docobj<Tag>(L, 1);
   const char* name = lua_tostring(L, 2);
   if (name) {
-    Tx tx;
+    Tx tx(tag->sprite());
     tx(new cmd::SetTagName(tag, name));
     tx.commit();
   }
@@ -131,7 +131,7 @@ int Tag_set_aniDir(lua_State* L)
 {
   auto tag = get_docobj<Tag>(L, 1);
   const int aniDir = lua_tointeger(L, 2);
-  Tx tx;
+  Tx tx(tag->sprite());
   tx(new cmd::SetTagAniDir(tag, (doc::AniDir)aniDir));
   tx.commit();
   return 0;
@@ -141,7 +141,7 @@ int Tag_set_repeats(lua_State* L)
 {
   auto tag = get_docobj<Tag>(L, 1);
   const int repeat = lua_tointeger(L, 2);
-  Tx tx;
+  Tx tx(tag->sprite());
   tx(new cmd::SetTagRepeat(tag, repeat));
   tx.commit();
   return 0;

src/app/script/tile_class.cpp

@@ -60,7 +60,7 @@ int Tile_set_image(lua_State* L)
   ImageRef newImage(Image::createCopy(srcImage));
 
   if (ts && ts->sprite()) {
-    Tx tx;
+    Tx tx(ts->sprite());
     tx(new cmd::ReplaceImage(ts->sprite(),
                              ts->get(tile->ti),
                              newImage));
@@ -125,8 +125,8 @@ int Tile_set_data(lua_State* L)
   doc::UserData ud = ts->getTileData(tile->ti);
   ud.setText(text);
 
-  if (ts->sprite()) {           // TODO use transaction in this sprite
-    Tx tx;
+  if (ts->sprite()) {
+    Tx tx(ts->sprite());
     tx(new cmd::SetTileData(ts, tile->ti, ud));
     tx.commit();
   }
@@ -148,8 +148,8 @@ int Tile_set_color(lua_State* L)
   doc::UserData ud = ts->getTileData(tile->ti);
   ud.setColor(docColor);
 
-  if (ts->sprite()) {           // TODO use transaction in this sprite
-    Tx tx;
+  if (ts->sprite()) {
+    Tx tx(ts->sprite());
     tx(new cmd::SetTileData(ts, tile->ti, ud));
     tx.commit();
   }
@@ -168,7 +168,7 @@ int Tile_set_properties(lua_State* L)
 
   auto newProperties = get_value_from_lua<doc::UserData::Properties>(L, 2);
   if (ts->sprite()) {
-    Tx tx;
+    Tx tx(ts->sprite());
     tx(new cmd::SetTileDataProperties(ts, tile->ti,
                                       std::string(),
                                       std::move(newProperties)));

src/app/script/tileset_class.cpp

@@ -68,7 +68,7 @@ int Tileset_set_name(lua_State* L)
 {
   auto tileset = get_docobj<Tileset>(L, 1);
   if (const char* newName = lua_tostring(L, 2)) {
-    Tx tx;
+    Tx tx(tileset->sprite());
     tx(new cmd::SetTilesetName(tileset, newName));
     tx.commit();
   }
@@ -93,7 +93,7 @@ int Tileset_set_baseIndex(lua_State* L)
 {
   auto tileset = get_docobj<Tileset>(L, 1);
   int i = lua_tointeger(L, 2);
-  Tx tx;
+  Tx tx(tileset->sprite());
   tx(new cmd::SetTilesetBaseIndex(tileset, i));
   tx.commit();
   return 0;

src/app/script/userdata.h

@@ -63,13 +63,12 @@ int UserData_get_properties(lua_State* L) {
 template<typename T>
 int UserData_set_text(lua_State* L) {
   auto obj = get_docobj<T>(L, 1);
-  auto spr = obj->sprite();
   const char* text = lua_tostring(L, 2);
   auto wud = get_WithUserData<T>(obj);
   UserData ud = wud->userData();
   ud.setText(text ? std::string(text): std::string());
-  if (spr) {
-    Tx tx;
+  if (auto spr = obj->sprite()) {
+    Tx tx(spr);
     tx(new cmd::SetUserData(wud, ud, static_cast<Doc*>(spr->document())));
     tx.commit();
   }
@@ -82,13 +81,12 @@ int UserData_set_text(lua_State* L) {
 template<typename T>
 int UserData_set_color(lua_State* L) {
   auto obj = get_docobj<T>(L, 1);
-  auto spr = obj->sprite();
   doc::color_t docColor = convert_args_into_pixel_color(L, 2, doc::IMAGE_RGB);
   auto wud = get_WithUserData<T>(obj);
   UserData ud = wud->userData();
   ud.setColor(docColor);
-  if (spr) {
-    Tx tx;
+  if (auto spr = obj->sprite()) {
+    Tx tx(spr);
     tx(new cmd::SetUserData(wud, ud, static_cast<Doc*>(spr->document())));
     tx.commit();
   }
@@ -103,8 +101,8 @@ int UserData_set_properties(lua_State* L) {
   auto obj = get_docobj<T>(L, 1);
   auto wud = get_WithUserData<T>(obj);
   auto newProperties = get_value_from_lua<doc::UserData::Properties>(L, 2);
-  if (obj->sprite()) {
-    Tx tx;
+  if (auto spr = obj->sprite()) {
+    Tx tx(spr);
     tx(new cmd::SetUserDataProperties(wud,
                                       std::string(),
                                       std::move(newProperties)));

src/app/sprite_job.cpp

@@ -17,7 +17,7 @@ SpriteJob::SpriteJob(const ContextReader& reader, const char* jobName)
   , m_writer(reader, 500)
   , m_document(m_writer.document())
   , m_sprite(m_writer.sprite())
-  , m_tx(m_writer.context(), jobName, ModifyDocument)
+  , m_tx(m_writer, jobName, ModifyDocument)
 {
 }
 

src/app/tx.h

@@ -11,8 +11,11 @@
 
 #include "app/app.h"
 #include "app/context.h"
+#include "app/context_access.h"
 #include "app/doc.h"
+#include "app/doc_access.h"
 #include "app/transaction.h"
+#include "doc/sprite.h"
 
 #include <stdexcept>
 
@@ -22,36 +25,76 @@ namespace app {
   // transaction in the context.
   class Tx {
   public:
+    enum LockAction {
+      DocIsLocked, // The doc is locked to be written
+      LockDoc,     // We have to lock the doc in Tx() ctor to write it
+      DontLockDoc, // In case that we are going for a step-by-step
+                   // transaction (e.g. ToolLoop or PixelsMovement)
+    };
+
     static constexpr const char* kDefaultTransactionName = "Transaction";
 
-    Tx(Context* ctx,
+    Tx() = delete;
+
+    Tx(const LockAction lockAction,
+       Context* ctx,
+       Doc* doc,
        const std::string& label = kDefaultTransactionName,
        const Modification mod = ModifyDocument)
     {
-      m_doc = ctx->activeDocument();
+      m_doc = doc;
       if (!m_doc)
-        throw std::runtime_error("No active document to execute a transaction");
+        throw std::runtime_error("No document to execute a transaction");
 
       m_transaction = m_doc->transaction();
-      if (m_transaction)
+      if (m_transaction) {
         m_owner = false;
+      }
       else {
+        if (lockAction == LockDoc) {
+          if (!m_doc->writeLock(500))
+            throw CannotWriteDocException();
+          m_locked = true;
+        }
+
         m_transaction = new Transaction(ctx, m_doc, label, mod);
         m_doc->setTransaction(m_transaction);
         m_owner = true;
       }
     }
 
-    // Use the default App context
-    Tx(const std::string& label = kDefaultTransactionName,
+  public:
+    Tx(Doc* doc,
+       const std::string& label = kDefaultTransactionName,
        const Modification mod = ModifyDocument)
-      : Tx(App::instance()->context(), label, mod) {
+      : Tx(LockDoc, doc->context(), doc, label, mod)
+    {
+    }
+
+    Tx(doc::Sprite* spr,
+       const std::string& label = kDefaultTransactionName,
+       const Modification mod = ModifyDocument)
+      : Tx(static_cast<Doc*>(spr->document()), label, mod)
+    {
+    }
+
+    // Use active document of the given context
+    Tx(ContextWriter& writer,
+       const std::string& label = kDefaultTransactionName,
+       const Modification mod = ModifyDocument)
+      : Tx(DocIsLocked,
+           writer.context(),
+           writer.document(), label, mod)
+    {
     }
 
     ~Tx() {
       if (m_owner) {
         m_doc->setTransaction(nullptr);
         delete m_transaction;
+
+        if (m_locked)
+          m_doc->unlock();
       }
     }
 
@@ -84,7 +127,8 @@ namespace app {
   private:
     Doc* m_doc;
     Transaction* m_transaction;
-    bool m_owner;               // Owner of the transaction
+    bool m_locked = false; // The doc was locked here
+    bool m_owner = false;  // Owner of the transaction
   };
 
 } // namespace app

src/app/ui/color_bar.cpp

@@ -892,7 +892,7 @@ void ColorBar::onRemapPalButtonClick()
     if (sprite) {
       ASSERT(sprite->pixelFormat() == IMAGE_INDEXED);
 
-      Tx tx(writer.context(), "Remap Colors", ModifyDocument);
+      Tx tx(writer, "Remap Colors", ModifyDocument);
       bool remapPixels = true;
 
       std::vector<ImageRef> images;
@@ -1003,7 +1003,7 @@ void ColorBar::onRemapTilesButtonClick()
       return;
     }
 
-    Tx tx(writer.context(), Strings::color_bar_remap_tiles(), ModifyDocument);
+    Tx tx(writer, Strings::color_bar_remap_tiles(), ModifyDocument);
     if (!existMapToEmpty &&
         remap.isInvertible(usedTiles)) {
       tx(new cmd::RemapTilemaps(tileset, remap));
@@ -1090,7 +1090,7 @@ void ColorBar::setPalette(const doc::Palette* newPalette, const std::string& act
     frame_t frame = writer.frame();
     if (sprite &&
         newPalette->countDiff(sprite->palette(frame), nullptr, nullptr)) {
-      Tx tx(writer.context(), actionText, ModifyDocument);
+      Tx tx(writer, actionText, ModifyDocument);
       tx(new cmd::SetPalette(sprite, frame, newPalette));
       tx.commit();
     }
@@ -1110,7 +1110,7 @@ void ColorBar::setTransparentIndex(int index)
         sprite->pixelFormat() == IMAGE_INDEXED &&
         int(sprite->transparentColor()) != index) {
       // TODO merge this code with SpritePropertiesCommand
-      Tx tx(writer.context(), "Set Transparent Color");
+      Tx tx(writer, "Set Transparent Color");
       DocApi api = writer.document()->getApi(tx);
       api.setSpriteTransparentColor(sprite, index);
       tx.commit();
@@ -1209,7 +1209,7 @@ void ColorBar::onTilesViewClearTiles(const doc::PalettePicks& _picks)
     if (sprite) {
       auto tileset = m_tilesView.tileset();
 
-      Tx tx(writer.context(), "Clear Tiles", ModifyDocument);
+      Tx tx(writer, "Clear Tiles", ModifyDocument);
       for (int ti=int(picks.size())-1; ti>=0; --ti) {
         if (picks[ti])
           tx(new cmd::RemoveTile(tileset, ti));
@@ -1240,7 +1240,7 @@ void ColorBar::onTilesViewResize(const int newSize)
     if (sprite) {
       auto tileset = m_tilesView.tileset();
 
-      Tx tx(writer.context(), Strings::color_bar_resize_tiles(), ModifyDocument);
+      Tx tx(writer, Strings::color_bar_resize_tiles(), ModifyDocument);
       if (tileset->size() < newSize) {
         for (doc::tile_index ti=tileset->size(); ti<newSize; ++ti) {
           ImageRef img = tileset->makeEmptyTile();
@@ -1281,7 +1281,7 @@ void ColorBar::onTilesViewDragAndDrop(doc::Tileset* tileset,
     Context* ctx = UIContext::instance();
     InlineCommandExecution inlineCmd(ctx);
     ContextWriter writer(ctx, 500);
-    Tx tx(writer.context(), Strings::color_bar_drag_and_drop_tiles(), ModifyDocument);
+    Tx tx(writer, Strings::color_bar_drag_and_drop_tiles(), ModifyDocument);
     if (isCopy)
       copy_tiles_in_tileset(tx, tileset, picks, currentEntry, beforeIndex);
     else
@@ -1880,7 +1880,7 @@ void ColorBar::updateCurrentSpritePalette(const char* operationName)
           cmd.release()->execute(UIContext::instance());
         }
         else {
-          Tx tx(writer.context(), operationName, ModifyDocument);
+          Tx tx(writer, operationName, ModifyDocument);
           // If tx() fails it will delete the cmd anyway, so we can
           // release the unique pointer here.
           tx(cmd.release());

src/app/ui/doc_view.cpp

@@ -594,7 +594,8 @@ bool DocView::onPaste(Context* ctx)
   auto clipboard = ctx->clipboard();
   if (clipboard->format() == ClipboardFormat::Image ||
       clipboard->format() == ClipboardFormat::Tilemap) {
-    clipboard->paste(ctx, true);
+    ContextWriter writer(ctx);
+    clipboard->paste(writer, true);
     return true;
   }
   else
@@ -630,7 +631,7 @@ bool DocView::onClear(Context* ctx)
 
   // TODO This code is similar to clipboard::cut()
   {
-    Tx tx(writer.context(), "Clear");
+    Tx tx(writer, "Clear");
     const bool deselectMask =
       (visibleMask &&
        !Preferences::instance().selection.keepSelectionAfterClear());

src/app/ui/editor/moving_cel_state.cpp

@@ -153,7 +153,7 @@ bool MovingCelState::onMouseUp(Editor* editor, MouseMessage* msg)
   if (modified) {
     {
       ContextWriter writer(m_reader, 1000);
-      Tx tx(writer.context(), "Cel Movement", ModifyDocument);
+      Tx tx(writer, "Cel Movement", ModifyDocument);
       DocApi api = document->getApi(tx);
       gfx::Point intOffset = intCelOffset();
 

src/app/ui/editor/moving_selection_state.cpp

@@ -82,7 +82,7 @@ EditorState::LeaveAction MovingSelectionState::onLeaveState(Editor* editor, Edit
   else {
     {
       ContextWriter writer(UIContext::instance(), 1000);
-      Tx tx(writer.context(), "Move Selection Edges", DoesntModifyDocument);
+      Tx tx(writer, "Move Selection Edges", DoesntModifyDocument);
       tx(new cmd::SetMaskPosition(doc, newOrigin));
       tx.commit();
     }

src/app/ui/editor/moving_slice_state.cpp

@@ -55,7 +55,7 @@ bool MovingSliceState::onMouseUp(Editor* editor, MouseMessage* msg)
 {
   {
     ContextWriter writer(UIContext::instance(), 1000);
-    Tx tx(writer.context(), "Slice Movement", ModifyDocument);
+    Tx tx(writer, "Slice Movement", ModifyDocument);
 
     for (const auto& item : m_items) {
       item.slice->insert(m_frame, item.oldKey);

src/app/ui/editor/pixels_movement.cpp

@@ -119,7 +119,8 @@ PixelsMovement::PixelsMovement(
   : m_reader(context)
   , m_site(site)
   , m_document(site.document())
-  , m_tx(context, operationName)
+  , m_tx(Tx::DontLockDoc, context,
+         context->activeDocument(), operationName)
   , m_isDragging(false)
   , m_adjustPivot(false)
   , m_handle(NoHandle)

src/app/ui/editor/tool_loop_impl.cpp

@@ -477,7 +477,9 @@ public:
                const bool saveLastPoint)
     : ToolLoopBase(editor, site, grid, params)
     , m_context(context)
-    , m_tx(m_context,
+    , m_tx(Tx::DontLockDoc,
+           m_context,
+           m_context->activeDocument(),
            m_tool->getText().c_str(),
            ((m_ink->isSelection() ||
              m_ink->isEyedropper() ||

src/app/ui/timeline/timeline.cpp

@@ -1387,7 +1387,8 @@ bool Timeline::onProcessMessage(Message* msg)
             if (tag) {
               if ((m_state == STATE_RESIZING_TAG_LEFT && tag->fromFrame() != m_resizeTagData.from) ||
                   (m_state == STATE_RESIZING_TAG_RIGHT && tag->toFrame() != m_resizeTagData.to)) {
-                Tx tx(UIContext::instance(), Strings::commands_FrameTagProperties());
+                ContextWriter writer(UIContext::instance());
+                Tx tx(writer, Strings::commands_FrameTagProperties());
                 tx(new cmd::SetTagRange(
                      tag,
                      (m_state == STATE_RESIZING_TAG_LEFT ? m_resizeTagData.from: tag->fromFrame()),
@@ -4389,7 +4390,9 @@ bool Timeline::onPaste(Context* ctx)
       m_redrawMarchingAntsOnly = false;
       invalidate();
     }
-    clipboard->paste(ctx, true);
+
+    ContextWriter writer(ctx);
+    clipboard->paste(writer, true);
     return true;
   }
   else

src/app/util/clipboard.cpp

@@ -362,7 +362,7 @@ void Clipboard::cut(ContextWriter& writer)
   else {
     // TODO This code is similar to DocView::onClear()
     {
-      Tx tx(writer.context(), "Cut");
+      Tx tx(writer, "Cut");
       Site site = writer.context()->activeSite();
       CelList cels;
       if (site.range().enabled()) {
@@ -461,10 +461,10 @@ void Clipboard::copyPalette(const Palette* palette,
   m_data->picks = picks;
 }
 
-void Clipboard::paste(Context* ctx,
+void Clipboard::paste(ContextWriter& writer,
                       const bool interactive)
 {
-  Site site = ctx->activeSite();
+  const Site site = *writer.site();
   Doc* dstDoc = site.document();
   if (!dstDoc)
     return;
@@ -531,7 +531,7 @@ void Clipboard::paste(Context* ctx,
         if (!dstLayer || !dstLayer->isImage())
           return;
 
-        Tx tx(ctx, "Paste Image");
+        Tx tx(writer, "Paste Image");
         DocApi api = dstDoc->getApi(tx);
         Cel* dstCel = api.addCel(
           static_cast<LayerImage*>(dstLayer), site.frame(),
@@ -611,7 +611,7 @@ void Clipboard::paste(Context* ctx,
             break;
           }
 
-          Tx tx(ctx, "Paste Cels");
+          Tx tx(writer, "Paste Cels");
           DocApi api = dstDoc->getApi(tx);
 
           // Add extra frames if needed
@@ -671,7 +671,7 @@ void Clipboard::paste(Context* ctx,
             break;
           }
 
-          Tx tx(ctx, "Paste Frames");
+          Tx tx(writer, "Paste Frames");
           DocApi api = dstDoc->getApi(tx);
 
           auto srcLayers = srcSpr->allBrowsableLayers();
@@ -714,7 +714,7 @@ void Clipboard::paste(Context* ctx,
           if (srcDoc->colorMode() != dstDoc->colorMode())
             throw std::runtime_error("You cannot copy layers of document with different color modes");
 
-          Tx tx(ctx, "Paste Layers");
+          Tx tx(writer, "Paste Layers");
           DocApi api = dstDoc->getApi(tx);
 
           // Remove children if their parent is selected so we only

src/app/util/clipboard.h

@@ -74,7 +74,8 @@ namespace app {
                      const doc::Tileset* tileset);
     void copyPalette(const doc::Palette* palette,
                      const doc::PalettePicks& picks);
-    void paste(Context* ctx, const bool interactive);
+    void paste(ContextWriter& writer,
+               const bool interactive);
 
     doc::ImageRef getImage(doc::Palette* palette);
 

src/app/util/layer_boundaries.cpp

@@ -121,7 +121,7 @@ void select_layer_boundaries(Layer* layer,
       }
     }
 
-    Tx tx(writer.context(), "Select Layer Boundaries", DoesntModifyDocument);
+    Tx tx(writer, "Select Layer Boundaries", DoesntModifyDocument);
     tx(new cmd::SetMask(doc, &newMask));
     tx.commit();
 

src/doc/sprite.h

@@ -105,7 +105,7 @@ namespace doc {
     void setColorSpace(const gfx::ColorSpaceRef& colorSpace);
 
     // This method is only required/used for the template functions app::script::UserData_set_text/color.
-    const Sprite* sprite() const { return this; }
+    Sprite* sprite() const { return const_cast<Sprite*>(this); }
 
     // Returns true if the sprite has a background layer and it's visible
     bool isOpaque() const;