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Implementing the APNG Render Feature

Hi everyone, So, I'm currently trying to implement APNG Specification , but I have some problems with rendering frames. My function

private void UpdateUI() { foreach (PictureBox pb in pics) { APNGBox box = (APNGBox)pb.Tag; APNGLib.APNG png = box.png; if (box.buffer == null) { box.buffer = new Bitmap((int)png.Width, (int)png.Height); } APNGLib.Frame f = png.GetFrame(box.frameNum); using (Graphics g = Graphics.FromImage(box.buffer)) { switch (f.DisposeOp) { case APNGLib.Frame.DisposeOperation.NONE: break; case APNGLib.Frame.DisposeOperation.BACKGROUND: g.Clear(Color.Transparent); break; case APNGLib.Frame.DisposeOperation.PREVIOUS: if (box.prevBuffer != null) { g.DrawImage(box.prevBuffer, Point.Empty); } else { g.Clear(Color.Transparent); } break; default: break; } Bitmap read = png.ToBitmap(box.frameNum++); switch (f.BlendOp) { case APNGLib.Frame.BlendOperation.OVER: g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceOver; break; case APNGLib.Frame.BlendOperation.SOURCE: g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy; break; default: break; } g.DrawImage(read, new Point((int)f.XOffset, (int)f.YOffset)); } box.prevBuffer = box.buffer; pb.Image = box.buffer; if (box.frameNum >= box.png.FrameCount) { box.frameNum = 0; box.buffer = null; box.prevBuffer = null; } } }

APNGBox -

 internal class APNGBox { public int frameNum = 0; public APNGLib.APNG png; public Bitmap buffer; public Bitmap prevBuffer; }

I think this is basically correct as I used it for all the images in the APNG Gallery . However, some of them do not display correctly ( There are problems with the artifact in this , and this one does not save the red bar on the left sequentially). Please note: you will have a page view in Firefox 3 or higher to view the animation.

I am convinced that the problem is related to the way I handle DISPOSE_OP_PREVIOUS, but I cannot understand what I'm doing wrong. Can anyone suggest that I might lose?

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So, I was able to figure this out, and publish it here if someone in the future encounters a similar problem. It turns out the problem was mostly threefold:

  • Do not change the "previous buffer" if the frame type is "PREVIOUS"
  • Use the previous dispose_op frame rather than the dispose_op frame of the current frame to determine how it is managing
  • Be sure to delete only the old frame area, not the entire frame

New code:

  internal class APNGBox { public int frameNum { get; set; } public APNGLib.APNG apng { get; set; } public Bitmap buffer { get; set; } public Bitmap prevBuffer { get; set; } public APNGBox(APNGLib.APNG png) { frameNum = 0; apng = png; buffer = apng.ToBitmap(0); prevBuffer = null; } } private void UpdateUI() { foreach (PictureBox pb in pics) { APNGBox box = (APNGBox)pb.Tag; APNGLib.APNG png = box.apng; if (!png.IsAnimated) { if (pb.Image == null) { pb.Image = png.ToBitmap(); } } else { if (box.frameNum != png.FrameCount - 1) { Bitmap prev = box.prevBuffer == null ? null : new Bitmap(box.prevBuffer); APNGLib.Frame f1 = png.GetFrame(box.frameNum); if (f1.DisposeOp != APNGLib.Frame.DisposeOperation.PREVIOUS) { box.prevBuffer = new Bitmap(box.buffer); } DisposeBuffer(box.buffer, new Rectangle((int)f1.XOffset, (int)f1.YOffset, (int)f1.Width, (int)f1.Height), f1.DisposeOp, prev); box.frameNum++; APNGLib.Frame f2 = png.GetFrame(box.frameNum); RenderNextFrame(box.buffer, new Point((int)f2.XOffset, (int)f2.YOffset), png.ToBitmap(box.frameNum), f2.BlendOp); } else { box.frameNum = 0; box.prevBuffer = null; ClearFrame(box.buffer); RenderNextFrame(box.buffer, Point.Empty, png.ToBitmap(box.frameNum), APNGLib.Frame.BlendOperation.SOURCE); } pb.Invalidate(); } } } private void DisposeBuffer(Bitmap buffer, Rectangle region, APNGLib.Frame.DisposeOperation dispose, Bitmap prevBuffer) { using (Graphics g = Graphics.FromImage(buffer)) { g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy; Brush b = new SolidBrush(Color.Transparent); switch (dispose) { case APNGLib.Frame.DisposeOperation.NONE: break; case APNGLib.Frame.DisposeOperation.BACKGROUND: g.FillRectangle(b, region); break; case APNGLib.Frame.DisposeOperation.PREVIOUS: if(prevBuffer != null) { g.FillRectangle(b, region); g.DrawImage(prevBuffer, region, region, GraphicsUnit.Pixel); } break; default: break; } } } private void RenderNextFrame(Bitmap buffer, Point point, Bitmap nextFrame, APNGLib.Frame.BlendOperation blend) { using(Graphics g = Graphics.FromImage(buffer)) { switch(blend) { case APNGLib.Frame.BlendOperation.OVER: g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceOver; break; case APNGLib.Frame.BlendOperation.SOURCE: g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy; break; default: break; } g.DrawImage(nextFrame, point); } } private void ClearFrame(Bitmap buffer) { using(Graphics g = Graphics.FromImage(buffer)) { g.Clear(Color.Transparent); } }
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