imageviewer: fix animated gifs handling

If disposal method is set to BACKGROUND one would expect that
canvas should be restored to global background color. That is
what gif standard suggests. Most (all?) decoders however treat
this as reseting canvas to transparency or fixed, decoder
specific background color. Virtually all gifs are prepared with
this in mind so to not break them we can't follow standard here.

Change-Id: I90ca712bba89d4190771eb5320eabda353d3e2bb

2 files changed, 10 insertions, 23 deletions

diff --git a/apps/plugins/imageviewer/gif/gif.c b/apps/plugins/imageviewer/gif/gif.c
index c3cad71..31fd11d 100644
--- a/apps/plugins/imageviewer/gif/gif.c
+++ b/apps/plugins/imageviewer/gif/gif.c
@@ -110,10 +110,9 @@ static int load_image(char *filename, struct image_info *info,
 
             if (!iv->running_slideshow)
             {
-                rb->lcd_putsf(0, 2, "image %dx%d",
-                              p_decoder->width,
-                              p_decoder->height);
-                rb->lcd_putsf(0, 3, "decoding %d*%d",
+                rb->lcd_putsf(0, 2, "file: %s",
+                              filename);
+                rb->lcd_putsf(0, 3, "size: %dx%d",
                               p_decoder->width,
                               p_decoder->height);
                 rb->lcd_update();
diff --git a/apps/plugins/imageviewer/gif/gif_decoder.c b/apps/plugins/imageviewer/gif/gif_decoder.c
index 74330c3..e45814c 100644
--- a/apps/plugins/imageviewer/gif/gif_decoder.c
+++ b/apps/plugins/imageviewer/gif/gif_decoder.c
@@ -125,30 +125,18 @@ void gif_open(char *filename, struct gif_decoder *d)
     d->frames_count = 0;
 }
 
-static void set_canvas_background(GifPixelType *Line, pixel_t *out,
-                                  GifFileType *GifFile)
+static void set_canvas_background(pixel_t *out, GifFileType *GifFile)
 {
-    int i;
-
     /* Reading Gif spec it seems one should always use background color
      * in canvas but most real files omit this and sets background color to 0
      * (which IS valid index). We can choose to either conform to standard
      * (and wrongly display most of gifs with transparency) or stick to
      * common practise and treat background color 0 as transparent.
-     * I preffer the second.
+     * Moreover when dispose method is BACKGROUND spec suggest
+     * to reset canvas to global background color specified in gif BUT
+     * all renderers I know use transparency instead.
      */
-    if (GifFile->SColorMap && GifFile->SBackGroundColor != 0)
-    {
-        memset(Line, GifFile->SBackGroundColor, GifFile->SWidth);
-
-        for(i=0; i<GifFile->SHeight; i++)
-            gif2pixels(Line, out, i, 0, GifFile->SWidth);
-    }
-    else
-    {
-        memset(out, PIXEL_TRANSPARENT, PIXELS_SZ);    
-    }
-
+    memset(out, PIXEL_TRANSPARENT, PIXELS_SZ);    
 }
 
 /* var names adhere to giflib coding style */
@@ -212,7 +200,7 @@ void gif_decode(struct gif_decoder *d,
     }
 
     /* Global background color */
-    set_canvas_background(Line, pixels_buffer[0], GifFile);
+    set_canvas_background(pixels_buffer[0], GifFile);
 
     bm.width = GifFile->SWidth;
     bm.height = GifFile->SHeight;
@@ -335,7 +323,7 @@ void gif_decode(struct gif_decoder *d,
                     switch (GifFile->Image.GCB->DisposalMode)
                     {
                         case DISPOSE_BACKGROUND:
-                            set_canvas_background(Line, pixels_buffer[buf_idx],
+                            set_canvas_background(pixels_buffer[buf_idx],
                                                   GifFile);
                             break;