Add backward compatibility for color palette in .ase files

With this change we save the new palette chunk when it's necessary, and
the old color2 chunk will be always present only for backward
compatibility. (So we can open a .ase file saved with v1.1 in v1.0.)

src/app/file/ase_format.cpp

@@ -101,6 +101,7 @@ static void ase_file_write_close_chunk(FILE* f, ASE_Chunk* chunk);
 static Palette* ase_file_read_color_chunk(FILE* f, Palette* prevPal, frame_t frame);
 static Palette* ase_file_read_color2_chunk(FILE* f, Palette* prevPal, frame_t frame);
 static Palette* ase_file_read_palette_chunk(FILE* f, Palette* prevPal, frame_t frame);
+static void ase_file_write_color2_chunk(FILE* f, ASE_FrameHeader* frame_header, Palette* pal);
 static void ase_file_write_palette_chunk(FILE* f, ASE_FrameHeader* frame_header, Palette* pal, int from, int to);
 static Layer* ase_file_read_layer_chunk(FILE* f, Sprite* sprite, Layer** previous_layer, int* current_level);
 static void ase_file_write_layer_chunk(FILE* f, ASE_FrameHeader* frame_header, Layer* layer);
@@ -163,6 +164,7 @@ bool AseFormat::onLoad(FileOp* fop)
 {
   FileHandle handle(open_file_with_exception(fop->filename, "rb"));
   FILE* f = handle.get();
+  bool ignore_old_color_chunks = false;
 
   ASE_Header header;
   if (!ase_file_read_header(f, &header)) {
@@ -215,16 +217,17 @@ bool AseFormat::onLoad(FileOp* fop)
         switch (chunk_type) {
 
           case ASE_FILE_CHUNK_FLI_COLOR:
-          case ASE_FILE_CHUNK_FLI_COLOR2: {
-            Palette* prevPal = sprite->palette(frame);
-            UniquePtr<Palette> pal(chunk_type == ASE_FILE_CHUNK_FLI_COLOR ?
-                                   ase_file_read_color_chunk(f, prevPal, frame):
-                                   ase_file_read_color2_chunk(f, prevPal, frame));
+          case ASE_FILE_CHUNK_FLI_COLOR2:
+            if (!ignore_old_color_chunks) {
+              Palette* prevPal = sprite->palette(frame);
+              UniquePtr<Palette> pal(chunk_type == ASE_FILE_CHUNK_FLI_COLOR ?
+                                     ase_file_read_color_chunk(f, prevPal, frame):
+                                     ase_file_read_color2_chunk(f, prevPal, frame));
 
-            if (prevPal->countDiff(pal.get(), NULL, NULL) > 0)
-              sprite->setPalette(pal.get(), true);
+              if (prevPal->countDiff(pal.get(), NULL, NULL) > 0)
+                sprite->setPalette(pal.get(), true);
+            }
             break;
-          }
 
           case ASE_FILE_CHUNK_PALETTE: {
             Palette* prevPal = sprite->palette(frame);
@@ -232,6 +235,8 @@ bool AseFormat::onLoad(FileOp* fop)
 
             if (prevPal->countDiff(pal.get(), NULL, NULL) > 0)
               sprite->setPalette(pal.get(), true);
+
+            ignore_old_color_chunks = true;
             break;
           }
 
@@ -320,6 +325,14 @@ bool AseFormat::onSave(FileOp* fop)
   ase_file_prepare_header(f, &header, sprite);
   ase_file_write_header(f, &header);
 
+  bool require_new_palette_chunk = false;
+  for (Palette* pal : sprite->getPalettes()) {
+    if (pal->size() != 256 || pal->hasAlpha()) {
+      require_new_palette_chunk = true;
+      break;
+    }
+  }
+
   // Write frames
   for (frame_t frame(0); frame<sprite->totalFrames(); ++frame) {
     // Prepare the frame header
@@ -334,9 +347,14 @@ bool AseFormat::onSave(FileOp* fop)
     int palFrom = 0, palTo = pal->size()-1;
     if ((frame == 0 ||
          sprite->palette(frame-1)->countDiff(pal, &palFrom, &palTo) > 0)) {
-      // Write the color chunk
-      ase_file_write_palette_chunk(f, &frame_header,
-                                   pal, palFrom, palTo);
+      // Write new palette chunk
+      if (require_new_palette_chunk) {
+        ase_file_write_palette_chunk(f, &frame_header,
+                                     pal, palFrom, palTo);
+      }
+
+      // Write color chunk for backward compatibility only
+      ase_file_write_color2_chunk(f, &frame_header, pal);
     }
 
     // Write extra chunks in the first frame
@@ -679,6 +697,24 @@ static Palette* ase_file_read_palette_chunk(FILE* f, Palette* prevPal, frame_t f
   return pal;
 }
 
+static void ase_file_write_color2_chunk(FILE* f, ASE_FrameHeader* frame_header, Palette* pal)
+{
+  ChunkWriter chunk(f, frame_header, ASE_FILE_CHUNK_FLI_COLOR2);
+  int c, color;
+
+  fputw(1, f);                  // Number of packets
+
+  // First packet
+  fputc(0, f);                                   // skip 0 colors
+  fputc(pal->size() == 256 ? 0: pal->size(), f); // number of colors
+  for (c=0; c<pal->size(); c++) {
+    color = pal->getEntry(c);
+    fputc(rgba_getr(color), f);
+    fputc(rgba_getg(color), f);
+    fputc(rgba_getb(color), f);
+  }
+}
+
 static void ase_file_write_palette_chunk(FILE* f, ASE_FrameHeader* frame_header, Palette* pal, int from, int to)
 {
   ChunkWriter chunk(f, frame_header, ASE_FILE_CHUNK_PALETTE);

src/doc/palette.cpp

@@ -76,6 +76,14 @@ void Palette::addEntry(color_t color)
   setEntry(size()-1, color);
 }
 
+bool Palette::hasAlpha() const
+{
+  for (int i=0; i<(int)m_colors.size(); ++i)
+    if (rgba_geta(getEntry(i)) < 255)
+      return true;
+  return false;
+}
+
 void Palette::setFrame(frame_t frame)
 {
   ASSERT(frame >= 0);

src/doc/palette.h

@@ -38,6 +38,9 @@ namespace doc {
 
     int getModifications() const { return m_modifications; }
 
+    // Return true if the palette has alpha != 255 in some entry
+    bool hasAlpha() const;
+
     frame_t frame() const { return m_frame; }
     void setFrame(frame_t frame);