canvas.drawRect 未在图像上绘制矩形

Question

这里 canvas.drawRect 对不同的位图有不同的处理方式。我希望在顶部图像上绘制矩形，并希望矩形外部的图像部分变暗或模糊。请帮我。

draw.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Paint paint = new Paint();
            paint.setColor(Color.RED);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(2);

            Bitmap bitmap=((BitmapDrawable)image.getDrawable()).getBitmap();
            Bitmap mutableBitmap = bitmap.copy(Bitmap.Config.RGB_565, true);

            Bitmap bitmap1 = Bitmap.createBitmap(600,400, Bitmap.Config.RGB_565);

            Rect r = new Rect();
            r.set(100,100,500,300);

            Canvas canvas = new Canvas(mutableBitmap);
            Canvas canvas1 = new Canvas(bitmap1);

            canvas.drawRect(r,paint);
            canvas1.drawRect(r,paint);

            image.setImageBitmap(mutableBitmap);
            image1.setImageBitmap(bitmap1);

        }
 });

Answer 1

如果你想画一个矩形，把外面的部分变暗，就这样画。创建一个位图并绘制全尺寸半透明矩形，然后在内部绘制另一个全透明颜色的矩形。然后将该位图放在您的图像上。

试试这个代码：

            Bitmap bitmap = Bitmap.createBitmap(600,400,Bitmap.Config.ARGB_8888);
            Canvas canvas = new Canvas(bitmap);

            RectF outerRectangle = new RectF(0, 0, 600, 400);
            RectF innerRectangle = new RectF(100, 100, 500, 300);

            Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
            paint.setColor(Color.BLACK);
            paint.setAlpha(80);
            canvas.drawRect(outerRectangle, paint);

            paint.setColor(Color.TRANSPARENT);
            paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT));
            canvas.drawRect(innerRectangle, paint);

            paint.setColor(Color.RED);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(2);
            canvas.drawRect(innerRectangle, paint);

            image1.setImageBitmap(bitmap);

Answer 2

您已经接受了 Prasad 给出的答案，但该答案没有解决 post 的标题，该标题涉及 drawRect 在一个 Bitmap 上的工作，而不是另一个。我也遇到了在图像上绘制矩形的问题，我找到的解决方案是将矩形添加到路径，然后改用 drawPath。

Path boxPath = new Path();
boxPath.addRect(100, 100, 500, 300, Path.Direction.CW);
canvas.drawPath(boxPath, paint);

canvas.drawRect 未在图像上绘制矩形

canvas.drawRect Not drawing rectangle on image

java

android

android-canvas