BitmapDecoder should support gif

[seven332]

Only decode the first frame of the gif image, just like what skia does.

[inorichi]

What steps should be followed here? I have this in mind:

1. Decode the first frame completely (there's no line by line decoding nor regions)
2. Move the selected region (if there's any) to the beginning of the array (with memmove), so that we don't need to alloc more memory for a copy.
3. Create a new container for the scaled image.
4. Downscale the image (using the container as destination for the pixels) applying some filter: nearest, bilinear, bicubic, lanczos... which one?

[seven332]

GIF is an indexed-color image type. The result in your step 1 is the color-index array of the whole first frame (some image information as well). So the step 2 should be generating the selected region raw image(like RGBA array). Then step 3, downscale the image. Maybe the step 2 and the step 3 can combine to save memory.

Bilinear is good enough for downscaling. That is what Android OpenGL ES used in default.