学习一些常用的混合模式之BlendMode. dstIn

Keeps the destination pixels that cover source pixels, discards the remaining source and destination pixels

公式：

代码:

    canvas.saveLayer(Rect.fromLTWH(0, 0, width, height), Paint());
    Paint dstPaint = Paint()..color = Colors.red;
    dstPaint.style = ui.PaintingStyle.fill;
    canvas.drawImageRect(image1!, Rect.fromLTWH(0, 0, image!.width.toDouble(), image!.height.toDouble()), Rect.fromLTWH(0, 0, width/2, height/2), dstPaint);


    var srcPaint = Paint()
      ..color = Colors.red
      ..blendMode = ui.BlendMode.dstIn; // 源颜色：蓝色; // 混合模式
    canvas.drawRect(Rect.fromLTWH(0, 0, width, height).deflate(30), srcPaint);

    canvas.restore();

效果图:

可以看到重合部分保留了dst，非重合部分dst保留,src全部清空。