animation artifacts

[bluesoho16]

When animating with this APNG:
https://en.wikipedia.org/wiki/File:Animated_PNG_example_bouncing_beach_ball.png

Visible artifacts can be seen (dragging blue trail on bouncing ball). This is caused by not properly handling the "dispose_op" value (specifically, when "dispose_op" has value of "1":
https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_Frame_Control_Chunk

Here is my fix:
PngAnimationComposer.java

    ...
    private PngFrameControl currentFrame;
    private PngFrameControl previousFrame;
    ...

    public void completeFrame(Argb8888Bitmap frameImage) {
        Bitmap frame = PngAndroid.toBitmap(frameImage);
        Paint paint = null;
        Drawable d;
        Bitmap previous=null;

        if(previousFrame != null) {
            if (1 == previousFrame.disposeOp) {
                canvas.drawColor(0, PorterDuff.Mode.CLEAR);
            }

            if (2 == previousFrame.disposeOp) {
                previous = Bitmap.createBitmap(canvasBitmap, currentFrame.xOffset, currentFrame.yOffset, currentFrame.width, currentFrame.height); // or could use from frames?
            }
        }
        if (0 == currentFrame.blendOp) {
            paint = srcModePaint;
        }

       ...
        previousFrame = currentFrame;
        currentFrame = null;
    }

[aellerton]

Excellent! I'll integrate that. Thank you!

[aellerton]

@bluesoho16 Can you please post the complete PngAnimationComposer.java or a PR?

Thanks!

[marcos-dogonahorse]

For everyone that is having problem with this bug, please look at #3

@bluesoho16 you should be careful with
canvas.drawColor(0, PorterDuff.Mode.CLEAR);
because that would "clear" the whole screen which is not what it should be doing. It should be clearing only the region that the previous frame was drawn at