[lua] Add several properties to handle layer groups (fix aseprite/api#16)

New properties to manage groups/sublayers:
* Layer.layers: property to access sublayers of a group
* Layer.stackIndex: property with the index of the layer in the list
  of layers
* Layer.parent setter: to move the layer to other group

src/app/script/engine.h

@@ -39,6 +39,7 @@ namespace doc {
   class FrameTag;
   class Image;
   class Layer;
+  class LayerGroup;
   class Mask;
   class Palette;
   class Sprite;
@@ -119,6 +120,7 @@ namespace app {
   void push_cels(lua_State* L, doc::Sprite* sprite);
   void push_color_space(lua_State* L, const gfx::ColorSpace& cs);
   void push_doc_range(lua_State* L, Site& site);
+  void push_group_layers(lua_State* L, doc::LayerGroup* group);
   void push_image(lua_State* L, doc::Image* image);
   void push_images(lua_State* L, const doc::ObjectIds& images);
   void push_layers(lua_State* L, const doc::ObjectIds& layers);

src/app/script/layer_class.cpp

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018  Igara Studio S.A.
+// Copyright (C) 2018-2019  Igara Studio S.A.
 // Copyright (C) 2018  David Capello
 //
 // This program is distributed under the terms of
@@ -12,6 +12,8 @@
 #include "app/cmd/set_layer_blend_mode.h"
 #include "app/cmd/set_layer_name.h"
 #include "app/cmd/set_layer_opacity.h"
+#include "app/doc.h"
+#include "app/doc_api.h"
 #include "app/script/docobj.h"
 #include "app/script/engine.h"
 #include "app/script/luacpp.h"
@@ -63,6 +65,29 @@ int Layer_get_parent(lua_State* L)
   return 1;
 }
 
+int Layer_get_layers(lua_State* L)
+{
+  auto layer = get_docobj<Layer>(L, 1);
+  if (layer->isGroup())
+    push_group_layers(L, static_cast<LayerGroup*>(layer));
+  else
+    lua_pushnil(L);
+  return 1;
+}
+
+int Layer_get_stackIndex(lua_State* L)
+{
+  auto layer = get_docobj<Layer>(L, 1);
+  const auto& layers = layer->parent()->layers();
+  auto it = std::find(layers.begin(), layers.end(), layer);
+  ASSERT(it != layers.end());
+  if (it != layers.end())
+    lua_pushinteger(L, it - layers.begin() + 1);
+  else
+    lua_pushnil(L);
+  return 1;
+}
+
 int Layer_get_previous(lua_State* L)
 {
   auto layer = get_docobj<Layer>(L, 1);
@@ -219,6 +244,27 @@ int Layer_set_blendMode(lua_State* L)
   return 0;
 }
 
+int Layer_set_stackIndex(lua_State* L)
+{
+  auto layer = get_docobj<Layer>(L, 1);
+  int stackIndex = lua_tointeger(L, 2);
+  auto parent = layer->parent();
+
+  Layer* beforeThis = nullptr;
+  if (stackIndex < 1) {
+    beforeThis = parent->firstLayer();
+  }
+  else if (stackIndex <= int(parent->layers().size())) {
+    beforeThis = parent->layers()[stackIndex-1];
+  }
+
+  Doc* doc = static_cast<Doc*>(layer->sprite()->document());
+  Tx tx;
+  DocApi(doc, tx).restackLayerBefore(layer, parent, beforeThis);
+  tx.commit();
+  return 0;
+}
+
 int Layer_set_isEditable(lua_State* L)
 {
   auto layer = get_docobj<Layer>(L, 1);
@@ -254,6 +300,37 @@ int Layer_set_isExpanded(lua_State* L)
   return 0;
 }
 
+int Layer_set_parent(lua_State* L)
+{
+  auto layer = get_docobj<Layer>(L, 1);
+  LayerGroup* parent = nullptr;
+  if (auto sprite = may_get_docobj<Sprite>(L, 2)) {
+    parent = sprite->root();
+  }
+  else if (auto parentLayer = may_get_docobj<Layer>(L, 2)) {
+    if (parentLayer->isGroup())
+      parent = static_cast<LayerGroup*>(parentLayer);
+  }
+
+  if (parent == layer)
+    return luaL_error(L, "the parent of a layer cannot be the layer itself");
+
+  // TODO Why? should we be able to do this? It would require some hard work:
+  // 1. convert color modes
+  // 2. multiple transactions for both modified sprites?
+  if (parent->sprite() != layer->sprite())
+    return luaL_error(L, "you cannot move layers between sprites");
+
+  if (parent) {
+    Doc* doc = static_cast<Doc*>(layer->sprite()->document());
+    Tx tx;
+    DocApi(doc, tx).restackLayerAfter(
+      layer, parent, parent->lastLayer());
+    tx.commit();
+  }
+  return 0;
+}
+
 const luaL_Reg Layer_methods[] = {
   { "__eq", Layer_eq },
   { "cel", Layer_cel },
@@ -262,7 +339,9 @@ const luaL_Reg Layer_methods[] = {
 
 const Property Layer_properties[] = {
   { "sprite", Layer_get_sprite, nullptr },
-  { "parent", Layer_get_parent, nullptr },
+  { "parent", Layer_get_parent, Layer_set_parent },
+  { "layers", Layer_get_layers, nullptr },
+  { "stackIndex", Layer_get_stackIndex, Layer_set_stackIndex },
   { "previous", Layer_get_previous, nullptr },
   { "next", Layer_get_next, nullptr },
   { "name", Layer_get_name, Layer_set_name },

src/app/script/layers_class.cpp

@@ -28,7 +28,11 @@ struct LayersObj {
   ObjectIds layers;
 
   LayersObj(Sprite* sprite) {
-    for (const Layer* layer : sprite->allLayers())
+    for (const Layer* layer : sprite->root()->layers())
+      layers.push_back(layer->id());
+  }
+  LayersObj(LayerGroup* group) {
+    for (const Layer* layer : group->layers())
       layers.push_back(layer->id());
   }
   LayersObj(const ObjectIds& layers)
@@ -100,6 +104,11 @@ void push_sprite_layers(lua_State* L, Sprite* sprite)
   push_new<LayersObj>(L, sprite);
 }
 
+void push_group_layers(lua_State* L, LayerGroup* group)
+{
+  push_new<LayersObj>(L, group);
+}
+
 void push_layers(lua_State* L, const ObjectIds& layers)
 {
   push_new<LayersObj>(L, layers);