private Bitmap EncodeGif <T>(Color backgrnd, int minAlpha, int startIndex, int frameCount)
where T : GifEncoder
{
//预判大小
Rectangle rect = this.GetRect();
Bitmap canvas = new Bitmap(rect.Width, rect.Height, PixelFormat.Format32bppArgb);
string tempFileName = Path.GetTempFileName();
GifEncoder enc = (GifEncoder)Activator.CreateInstance(typeof(T), tempFileName, rect.Width, rect.Height);
//写入帧信息
for (int i = startIndex, j = startIndex + frameCount; i < j; i++)
{
if (i >= this.Frames.Count)
{
break;
}
IGifFrame frame = this.Frames[i];
if (frame == null)
{
continue;
}
PrepareFrame(canvas, frame, rect, backgrnd, minAlpha);
enc.AppendFrame(canvas, frame.Delay);
}
enc.Dispose();
return(Image.FromFile(tempFileName) as Bitmap);
}
private static Bitmap PrepareFrame(IGifFrame frame, Rectangle canvasRect, Color backgrnd, int minAlpha)
{
Bitmap gifFrame = new Bitmap(canvasRect.Width, canvasRect.Height, PixelFormat.Format32bppArgb);
PrepareFrame(gifFrame, frame, canvasRect, backgrnd, minAlpha);
return(gifFrame);
}
/// <summary>
/// 预处理帧坐标，生成新的图片。
/// </summary>
private static void PrepareFrame(Bitmap canvas, IGifFrame frame, Rectangle canvasRect, Color backgrnd, int minAlpha)
{
Graphics g = Graphics.FromImage(canvas);
if (backgrnd.A == 0xff) //背景色
{
g.Clear(backgrnd);
frame.Draw(g, canvasRect);
}
else //透明混合色
{
g.Clear(Color.Transparent);
Rectangle frameRect = frame.Region;
frameRect.Offset(-canvasRect.X, -canvasRect.Y);
frame.Draw(g, canvasRect);
BitmapData data = canvas.LockBits(new Rectangle(Point.Empty, canvas.Size), ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
unsafe
{
byte *buffer = (byte *)data.Scan0.ToPointer();
for (int y = frameRect.Top; y < frameRect.Bottom; y++)
{
for (int x = frameRect.Left; x < frameRect.Right; x++)
{
int i = 4 * x + y * data.Stride;
byte a = buffer[i + 3];
if (a <= minAlpha)
{
buffer[i] = buffer[i + 1] = buffer[i + 2] = buffer[i + 3] = 0;
}
else if (a < 0xff)
{
float al = a / 255f;
float be = (1 - al);
buffer[i] = (byte)(buffer[i] * al + backgrnd.B * be);
buffer[i + 1] = (byte)(buffer[i + 1] * al + backgrnd.G * be);
buffer[i + 2] = (byte)(buffer[i + 2] * al + backgrnd.R * be);
buffer[i + 3] = 0xff;
}
}
}
}
canvas.UnlockBits(data);
}
}
