SkiaSharp 设置图片透明度（笔记）

• 生成半透明水印图片，记录下代码。后续再整理
• 简单概括就是逐个像素进行Alpha值的设置

var folderPath ="D:\\"
using var watermarkMemoryStream = new MemoryStream();
var watermarkImgPath = Path.Combine(folderPath, "Content\\images\\HUNANDX\\watermark.png");
using var watermarkFile = System.IO.File.OpenRead(watermarkImgPath);// 读取文件 
using var fileStream = new SKManagedStream(watermarkFile);
using var bitmap = SKBitmap.Decode(fileStream);
//设置半透明
var transparent = new SKColor(0, 0, 0, 0);
for (int w = 0; w < bitmap.Width; w++)
{
    for (int h = 0; h < bitmap.Height; h++)
    {
        SKColor orgColor = bitmap.GetPixel(w, h);
        SKColor newColor = orgColor.Equals(transparent) ? orgColor : new SKColor(orgColor.Red, orgColor.Green, orgColor.Blue, 70);
        bitmap.SetPixel(w, h, newColor);
    }
}
using var resized = bitmap.Resize(new SKImageInfo(200, 80), SKFilterQuality.High);//重设大小
using var newImage = SKImage.FromBitmap(resized);
newImage.Encode(SKEncodedImageFormat.Png, 90).SaveTo(watermarkMemoryStream); // 保存文件 

思路来源于 System.Drawing.Image 的写法， 转载自：www.cnblogs.com/wyp1988/p/9…

public static Bitmap SetImageOpacity(Image srcImage, int opacity)
        {
            Bitmap pic = new Bitmap(srcImage);
            for (int w = 0; w < pic.Width; w++)
            {
                for (int h = 0; h < pic.Height; h++)
                {
                    Color c = pic.GetPixel(w, h);
                    Color newC;
                    if (!c.Equals(Color.FromArgb(0, 0, 0, 0)))
                    {
                        newC = Color.FromArgb(opacity, c);
                    }
                    else
                    {
                        newC = c;
                    }
                    pic.SetPixel(w, h, newC);
                }
            }
            return pic;
        }

        public static Image SetImageOpacity2(Image srcImage, int opacity)
        {
            Bitmap img = new Bitmap(srcImage);
            using (Bitmap bmp = new Bitmap(img.Width, img.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb))
            {
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    g.DrawImage(img, 0, 0);
                    for (int h = 0; h <= img.Height - 1; h++)
                    {
                        for (int w = 0; w <= img.Width - 1; w++)
                        {
                            Color c = img.GetPixel(w, h);
                            if (!c.Equals(Color.FromArgb(0, 0, 0, 0)))
                            {
                                bmp.SetPixel(w, h, Color.FromArgb(opacity, c.R, c.G, c.B));
                            }
                            else
                            {
                                bmp.SetPixel(w, h, Color.FromArgb(c.A, c.R, c.G, c.B));
                            }
                        }
                    }
                }
                return (Image)bmp.Clone();
            }
        }