Avoid loading current dithering matrix on each mouse move (related to #4174)

With this change we are reusing the cached/loaded matrix on each
DitheringMatrixInfo struct, calling the
load_dithering_matrix_from_sprite() function just one time (not on
each brush preview/mouse movement).

src/app/extensions.cpp

@@ -936,15 +936,15 @@ const render::DitheringMatrix* Extensions::ditheringMatrix(const std::string& ma
   return nullptr;
 }
 
-std::vector<Extension::DitheringMatrixInfo> Extensions::ditheringMatrices()
+std::vector<Extension::DitheringMatrixInfo*> Extensions::ditheringMatrices()
 {
-  std::vector<Extension::DitheringMatrixInfo> result;
+  std::vector<Extension::DitheringMatrixInfo*> result;
   for (auto ext : m_extensions) {
     if (!ext->isEnabled())      // Ignore disabled themes
       continue;
 
-    for (auto it : ext->m_ditheringMatrices)
+    for (auto& it : ext->m_ditheringMatrices)
-      result.push_back(it.second);
+      result.push_back(&it.second);
   }
   return result;
 }

src/app/extensions.h

@@ -222,7 +222,13 @@ namespace app {
     std::string palettePath(const std::string& palId);
     ExtensionItems palettes() const;
     const render::DitheringMatrix* ditheringMatrix(const std::string& matrixId);
-    std::vector<Extension::DitheringMatrixInfo> ditheringMatrices();
+
+    // The returned collection can be used temporarily while
+    // extensions are not installed/uninstalled. Each element is
+    // pointing to the real matrix info owned by extensions, this is
+    // needed to cache the matrix because it is lazy loaded from an
+    // image file. These pointers cannot be deleted.
+    std::vector<Extension::DitheringMatrixInfo*> ditheringMatrices();
 
     obs::signal<void(Extension*)> NewExtension;
     obs::signal<void(Extension*)> KeysChange;

src/app/ui/context_bar.cpp

@@ -1260,9 +1260,9 @@ public:
     bool found = false;
     auto ditheringMatrices = App::instance()
       ->extensions().ditheringMatrices();
-    for (const auto& it : ditheringMatrices) {
+    for (const auto* it : ditheringMatrices) {
-      if (it.name() == dynaPref.matrixName()) {
+      if (it->name() == dynaPref.matrixName()) {
-        m_dynamics.ditheringMatrix = it.matrix();
+        m_dynamics.ditheringMatrix = it->matrix();
         found = true;
         break;
       }

src/app/ui/dithering_selector.cpp

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019-2023  Igara Studio S.A.
+// Copyright (C) 2019-2024  Igara Studio S.A.
 // Copyright (C) 2017  David Capello
 //
 // This program is distributed under the terms of
@@ -217,25 +217,25 @@ void DitheringSelector::regenerate(int selectedItemIndex)
       addItem(new DitherItem(render::DitheringAlgorithm::None,
                              render::DitheringMatrix(),
                              Strings::dithering_selector_no_dithering()));
-      for (const auto& it : ditheringMatrices) {
+      for (const auto* it : ditheringMatrices) {
         try {
           addItem(new DitherItem(
             render::DitheringAlgorithm::Ordered,
-            it.matrix(),
+            it->matrix(),
-            Strings::dithering_selector_ordered_dithering() + it.name()));
+            Strings::dithering_selector_ordered_dithering() + it->name()));
         }
         catch (const std::exception& e) {
           LOG(ERROR, "%s\n", e.what());
           Console::showException(e);
         }
       }
-      for (const auto& it : ditheringMatrices) {
+      for (const auto* it : ditheringMatrices) {
         try {
           addItem(
             new DitherItem(
               render::DitheringAlgorithm::Old,
-              it.matrix(),
+              it->matrix(),
-              Strings::dithering_selector_old_dithering() + it.name()));
+              Strings::dithering_selector_old_dithering() + it->name()));
         }
         catch (const std::exception& e) {
           LOG(ERROR, "%s\n", e.what());
@@ -251,9 +251,9 @@ void DitheringSelector::regenerate(int selectedItemIndex)
     case SelectMatrix:
       addItem(new DitherItem(render::DitheringMatrix(),
                              Strings::dithering_selector_no_dithering()));
-      for (auto& it : ditheringMatrices) {
+      for (const auto* it : ditheringMatrices) {
         try {
-          addItem(new DitherItem(it.matrix(), it.name()));
+          addItem(new DitherItem(it->matrix(), it->name()));
         }
         catch (const std::exception& e) {
           LOG(ERROR, "%s\n", e.what());