Transparent GIFs with different layer sizes

[OzerOzdemir]

When a transparent gif has layers with different sizes, the animation looks off with lots of artifacts. This is present in multiple example sources, and also seems to be the original root cause of #631

The fix is to set x to pDraw->iX, similar to how y is set to y = pDraw->iY + pDraw->y; // current line

    if (pDraw->ucHasTransparency) // if transparency used
    {
      uint8_t *pEnd, c, ucTransparent = pDraw->ucTransparent;
      int x, iCount;
      pEnd = s + pDraw->iWidth;
      x = 0 // ----------- > This should be x = pDraw->iX;

[panki27]

The issue exists not in this library, but in https://github.com/bitbank2/AnimatedGIF (or rather the provided sample code).
While your fix has improved things, it didn't completely solve all the ghosting issues I had.

I found a workaround:

• Go to https://ezgif.com/optimize
• Upload your GIF that is not displaying correctly
• Choose "Unoptimize (coalesce)"
• Save the modified GIF

This will turn the GIF into a slideshow of full frames, no transparency or layers involved. After doing this, I got a 3100 frame GIF to play flawlessly.