Fix bug not re-using a tile when A=0 and RGB values are different

When alpha=0, we can ignore RGB values and re-use a tile in the
tileset.

src/app/util/cel_ops.cpp

@@ -405,6 +405,8 @@ void draw_image_into_new_tilemap_cel(
     if (grid.hasMask())
       mask_image(tileImage.get(), grid.mask().get());
 
+    preprocess_transparent_pixels(tileImage.get());
+
     doc::tile_index tileIndex;
     if (!tileset->findTileIndex(tileImage, tileIndex)) {
       auto addTile = new cmd::AddTile(tileset, tileImage);
@@ -538,6 +540,8 @@ void modify_tilemap_cel_region(
       if (grid.hasMask())
         mask_image(tileImage.get(), grid.mask().get());
 
+      preprocess_transparent_pixels(tileImage.get());
+
       tile_index tileIndex;
       if (tileset->findTileIndex(tileImage, tileIndex)) {
         // We can re-use an existent tile (tileIndex) from the tileset

src/doc/primitives.cpp

@@ -312,7 +312,7 @@ bool is_plain_image_templ(const Image* img, const color_t color)
   const LockImageBits<ImageTraits> bits(img);
   typename LockImageBits<ImageTraits>::const_iterator it, end;
   for (it=bits.begin(), end=bits.end(); it!=end; ++it) {
-    if (*it != color)
+    if (!ImageTraits::same_color(*it, color))
       return false;
   }
   ASSERT(it == end);
@@ -482,4 +482,31 @@ uint32_t calculate_image_hash(const Image* img, const gfx::Rect& bounds)
   return 0;
 }
 
+void preprocess_transparent_pixels(Image* image)
+{
+  switch (image->pixelFormat()) {
+
+    case IMAGE_RGB: {
+      LockImageBits<RgbTraits> bits(image);
+      auto it = bits.begin(), end = bits.end();
+      for (; it != end; ++it) {
+        if (rgba_geta(*it) == 0)
+          *it = 0;
+      }
+      break;
+    }
+
+    case IMAGE_GRAYSCALE: {
+      LockImageBits<RgbTraits> bits(image);
+      auto it = bits.begin(), end = bits.end();
+      for (; it != end; ++it) {
+        if (graya_geta(*it) == 0)
+          *it = 0;
+      }
+      break;
+    }
+
+  }
+}
+
 } // namespace doc

src/doc/primitives.h

@@ -1,5 +1,5 @@
 // Aseprite Document Library
-// Copyright (c) 2018-2019 Igara Studio S.A.
+// Copyright (c) 2018-2021 Igara Studio S.A.
 // Copyright (c) 2001-2016 David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -53,6 +53,10 @@ namespace doc {
   uint32_t calculate_image_hash(const Image* image,
                                 const gfx::Rect& bounds);
 
+  // Sets RGB values to 0 when alpha=0 (to match images with alpha=0
+  // in tilesets/calculate_image_hash)
+  void preprocess_transparent_pixels(Image* image);
+
 } // namespace doc
 
 #endif

src/doc/tileset.cpp

@@ -129,7 +129,9 @@ void Tileset::set(const tile_index ti,
 
   removeFromHash(ti, false);
 
+  preprocess_transparent_pixels(image.get());
   m_tiles[ti] = image;
+
   if (!m_hash.empty())
     hashImage(ti, image);
 }
@@ -140,6 +142,7 @@ tile_index Tileset::add(const ImageRef& image)
   ASSERT(image->width() == m_grid.tileSize().w);
   ASSERT(image->height() == m_grid.tileSize().h);
 
+  preprocess_transparent_pixels(image.get());
   m_tiles.push_back(image);
 
   const tile_index newIndex = tile_index(m_tiles.size()-1);
@@ -162,6 +165,7 @@ void Tileset::insert(const tile_index ti,
   ASSERT(image->height() == m_grid.tileSize().h);
 
   ASSERT(ti >= 0 && ti <= m_tiles.size()+1);
+  preprocess_transparent_pixels(image.get());
   m_tiles.insert(m_tiles.begin()+ti, image);
 
   if (!m_hash.empty()) {
@@ -256,6 +260,10 @@ void Tileset::notifyTileContentChange(const tile_index ti)
       // only way to make it work correctly)
 
   (void)ti;                     // unused
+
+  if (ti >= 0 && ti < m_tiles.size() && m_tiles[ti])
+    preprocess_transparent_pixels(m_tiles[ti].get());
+
   rehash();
 
 #endif

src/doc/tileset.h

@@ -95,6 +95,9 @@ namespace doc {
     // given "tileImage", this function returns true and the index of
     // that tile in the "ti" parameter. Returns false if the image is
     // not in the tileset.
+    //
+    // Warning: Use preprocess_transparent_pixels() with tileImage
+    // before calling this function.
     bool findTileIndex(const ImageRef& tileImage,
                        tile_index& ti);