Pinch滤镜是通过坐标变换来实现以某个点(cenX,cenY)为中心，某个半径R内图像向其挤压变形的效果。实现这个滤镜的算法很多，主要是数学公式的不同，大家可以自行设计，这里给个代码示例，大家可以直接使用。
//
/// <summary>
/// Pinch Filter
/// </summary>
/// <param name="src">Source image.</param>
/// <param name="cenX">The X position of sun.</param>
/// <param name="cenY">The Y position of sun.</param>
/// <returns>The result image.</returns>
private Bitmap PinchFilterProcess(Bitmap srcBitmap, int cenX, int cenY)
{
Bitmap a = new Bitmap(srcBitmap);
int w = a.Width;
int h = a.Height;
int radius = 0;
Bitmap dst = new Bitmap(w, h);
System.Drawing.Imaging.BitmapData srcData = a.LockBits(new Rectangle(0, 0, w, h), System.Drawing.Imaging.ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
System.Drawing.Imaging.BitmapData dstData = dst.LockBits(new Rectangle(0, 0, w, h), System.Drawing.Imaging.ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
unsafe
{
byte* pIn = (byte*)srcData.Scan0.ToPointer();
byte* pOut = (byte*)dstData.Scan0.ToPointer();
byte* p = null;
int sWidth = srcData.Stride;
int stride = sWidth - w * 4;
int offsetX = 0, offsetY = 0;
int newX = 0, newY = 0;
double radian = 0,degree = 10;
for (int y = 0; y < h; y++)
{
for (int x = 0; x < w; x++)
{
offsetX = x - cenX;
offsetY = y - cenY;
radian = Math.Atan2(offsetY, offsetX);
radius = (int)(Math.Sqrt(offsetX * offsetX + offsetY * offsetY));
radius = (int)(Math.Sqrt(radius) * degree);
newX = (int)(radius * Math.Cos(radian)) + cenX;
newY = (int)(radius * Math.Sin(radian)) + cenY;
newX = Math.Min(w - 1, Math.Max(0, newX));
newY = Math.Min(h - 1, Math.Max(0, newY));
p = pIn + newY * srcData.Stride + newX * 4;
pOut[0] = (byte)p[0];
pOut[1] = (byte)p[1];
pOut[2] = (byte)p[2];
pOut[3] = (byte)255;
pOut += 4;
}
pOut += stride;
}
a.UnlockBits(srcData);
dst.UnlockBits(dstData);
}
return dst;
}
