C# 检测PNG图片透明区域

将png decode为32位bitmap然后遍历像素

C# code

public Rect GetTransparentBounds(BitmapSource source) {    var width = source.PixelWidth;    var height = source.PixelHeight;    var pixelBytes = new byte[height * width * 4];    source.CopyPixels(pixelBytes, width * 4, 0);    double? ax1 = null, ax2 = null, ay1 = null, ay2 = null;    Rect result = new Rect();    for (int y = 0; y < height; y++) {        for (int x = 0; x < width; x++) {            byte a = pixelBytes[(y * width + x) * 4 + 3];            if (a != 0xff) {                if (ax1.HasValue) {                    ax1 = Math.Min(ax1.Value, x);                    ax2 = Math.Max(ax2.Value, x);                } else {                    ax1 = x;                    ax2 = x;                }                if (ay1.HasValue) {                    ay1 = Math.Min(ay1.Value, y);                    ay2 = Math.Max(ay2.Value, y);                } else {                    ay1 = y;                    ay2 = y;                }            }        };    }    if(ax1.HasValue && ay1.HasValue){        result.X = ax1.Value;        result.Y = ay1.Value;        result.Width = ax2.Value - ax1.Value;        result.Height = ay2.Value - ay1.Value;    }    return result;}