实现 APNG 渲染函数

Question

大家好， 所以，我目前正在尝试实现APNG Specification，但在帧渲染方面遇到了一些问题。我的功能是

    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 是

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

我认为这基本上是正确的，因为我已经针对APNG Gallery 中的所有图像运行了它。但是，其中一些渲染不正确（This 一个有伪影问题，this 一个没有始终如一地保留左侧的红色条）。请注意，您可以在 Firefox 3 或更高版本中查看页面以查看动画。

我相信这个问题与我处理 DISPOSE_OP_PREVIOUS 的方式有关，但我不知道我做错了什么。谁能建议我可能缺少什么？

Answer 1

所以，我最终能够弄清楚，并将在此处发布，以防将来有人遇到类似问题。事实证明，这个问题主要有三个方面：

1. 如果帧类型为“上一个”，则不应更改“上一个缓冲区”
2. 应该使用前一帧的 dispose_op，而不是当前帧的 dispose_op，来确定它的处理方式
3. 应该确保只处理旧框架的区域，而不是整个框架

新代码是：

    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);
        }
    }