Android，如何从Canvas获取像素颜色？

Question

我有这样的代码：

// ...

public class MyImageView extends ImageView

    public MyImageView(Context context, String value /* some other params */) {
        super(context);

        // some predefines
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        // some preparations
        try {
            // here I call third party lib like:
            someObj.draw(canvas);

            // HERE I WANT TO CHANGE COLOR OF SOME PIXELS ACCORDING TO THEIR CURRENT COLOR
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

代替UPCASE字母注释，我想在第三方lib绘制后根据其当前颜色更改画布上某些像素的颜色。 我可以使用canvas.drawPoint(x, y, paint)方法来设置像素颜色，但是如何通过(x,y)获得某个像素的颜色呢？

Answer 1

我可能在这里有一些东西（未经测试）：

public static Bitmap getBitmap(Canvas canvas) {
    // mBitmap is a private value inside Canvas.
    // time for some dirty reflection:
    try {
        java.lang.reflect.Field field = Canvas.class.getDeclaredField("mBitmap");
        field.setAccessible(true);
        return (Bitmap)field.get(canvas);
    }
    catch (Throwable t) {
        return null;
    }
}

然后，您可以通过以下方式访问像素：

Bitmap map = getBitmap(canvas);
if (map != null) {
    int rgb = map.getPixel(100,100);
    int red = android.graphics.Color.red(rgb);
    ...
}