Add support for 8-bit png files with alpha channel

src/app/file/file.cpp

@@ -776,6 +776,25 @@ void fop_sequence_get_color(FileOp *fop, int index, int *r, int *g, int *b)
   *b = rgba_getb(c);
 }
 
+void fop_sequence_set_alpha(FileOp* fop, int index, int a)
+{
+  int c = fop->seq.palette->getEntry(index);
+  int r = rgba_getr(c);
+  int g = rgba_getg(c);
+  int b = rgba_getb(c);
+
+  fop->seq.palette->setEntry(index, rgba(r, g, b, a));
+}
+
+void fop_sequence_get_alpha(FileOp* fop, int index, int* a)
+{
+  ASSERT(index >= 0);
+  if (index >= 0 && index < fop->seq.palette->size())
+    *a = rgba_geta(fop->seq.palette->getEntry(index));
+  else
+    *a = 0;
+}
+
 Image* fop_sequence_image(FileOp* fop, PixelFormat pixelFormat, int w, int h)
 {
   Sprite* sprite;

src/app/file/file.h

@@ -135,6 +135,8 @@ namespace app {
   void fop_sequence_set_format_options(FileOp* fop, const base::SharedPtr<FormatOptions>& format_options);
   void fop_sequence_set_color(FileOp* fop, int index, int r, int g, int b);
   void fop_sequence_get_color(FileOp* fop, int index, int *r, int *g, int *b);
+  void fop_sequence_set_alpha(FileOp* fop, int index, int a);
+  void fop_sequence_get_alpha(FileOp* fop, int index, int* a);
   Image* fop_sequence_image(FileOp* fi, PixelFormat pixelFormat, int w, int h);
 
   void fop_error(FileOp* fop, const char *error, ...);

src/app/file/png_format.cpp

@@ -39,7 +39,8 @@ class PngFormat : public FileFormat {
       FILE_SUPPORT_GRAY |
       FILE_SUPPORT_GRAYA |
       FILE_SUPPORT_INDEXED |
-      FILE_SUPPORT_SEQUENCES;
+      FILE_SUPPORT_SEQUENCES |
+      FILE_SUPPORT_PALETTE_WITH_ALPHA;
   }
 
   bool onLoad(FileOp* fop) override;
@@ -184,10 +185,6 @@ bool PngFormat::onLoad(FileOp* fop)
     return false;
   }
 
-  // Transparent palette entries
-  std::vector<uint8_t> pal_alphas(256, 255);
-  int mask_entry = -1;
-
   // Read the palette
   if (png_get_color_type(png_ptr, info_ptr) == PNG_COLOR_TYPE_PALETTE &&
       png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette)) {
@@ -206,17 +203,19 @@ bool PngFormat::onLoad(FileOp* fop)
     // Read alpha values for palette entries
     png_bytep trans = NULL;     // Transparent palette entries
     int num_trans = 0;
+    int mask_entry = -1;
 
     png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans, NULL);
 
     for (int i = 0; i < num_trans; ++i) {
-      pal_alphas[i] = trans[i];
+      fop_sequence_set_alpha(fop, i, trans[i]);
 
-      if (pal_alphas[i] < 128) {
+      if (trans[i] < 255) {
         fop->seq.has_alpha = true; // Is a transparent sprite
-
+        if (trans[i] == 0) {
-        if (mask_entry < 0)
+          if (mask_entry < 0)
-          mask_entry = i;
+            mask_entry = i;
+        }
       }
     }
 
@@ -225,8 +224,6 @@ bool PngFormat::onLoad(FileOp* fop)
       fop->document->sprite()->setTransparentColor(mask_entry);
   }
 
-  mask_entry = fop->document->sprite()->transparentColor();
-
   /* Allocate the memory to hold the image using the fields of info_ptr. */
 
    /* The easiest way to read the image: */
@@ -290,18 +287,10 @@ bool PngFormat::onLoad(FileOp* fop)
       else if (png_get_color_type(png_ptr, info_ptr) == PNG_COLOR_TYPE_PALETTE) {
         uint8_t* src_address = row_pointer;
         uint8_t* dst_address = (uint8_t*)image->getPixelAddress(0, y);
-        unsigned int x, c;
+        unsigned int x;
 
-        for (x=0; x<width; x++) {
+        for (x=0; x<width; x++)
-          c = *(src_address++);
+          *(dst_address++) = *(src_address++);
-
-          if (pal_alphas[c] < 128) {
-            *(dst_address++) = mask_entry;
-          }
-          else {
-            *(dst_address++) = c;
-          }
-        }
       }
 
       fop_progress(fop,
@@ -415,20 +404,24 @@ bool PngFormat::onSave(FileOp* fop)
     png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
 
     // If the sprite does not have a (visible) background layer, we
-    // include the alpha information of palette entries to indicate
+    // put alpha=0 to the transparent color.
-    // which is the transparent color.
+    int mask_entry = -1;
     if (fop->document->sprite()->backgroundLayer() == NULL ||
         !fop->document->sprite()->backgroundLayer()->isVisible()) {
-      int mask_entry = fop->document->sprite()->transparentColor();
+      mask_entry = fop->document->sprite()->transparentColor();
-      int num_trans = mask_entry+1;
-      png_bytep trans = (png_bytep)png_malloc(png_ptr, num_trans);
-
-      for (c = 0; c < num_trans; ++c)
-        trans[c] = (c == mask_entry ? 0: 255);
-
-      png_set_tRNS(png_ptr, info_ptr, trans, num_trans, NULL);
-      png_free(png_ptr, trans);
     }
+
+    int num_trans = PNG_MAX_PALETTE_LENGTH;
+    png_bytep trans = (png_bytep)png_malloc(png_ptr, num_trans);
+
+    for (c=0; c<num_trans; ++c) {
+      int alpha = 255;
+      fop_sequence_get_alpha(fop, c, &alpha);
+      trans[c] = (c == mask_entry ? 0: alpha);
+    }
+
+    png_set_tRNS(png_ptr, info_ptr, trans, num_trans, NULL);
+    png_free(png_ptr, trans);
   }
 
   /* Write the file header information. */