在缩放的画布上绘制图像

Question

我正在尝试在缩放的画布上绘制图像，用户触摸屏幕但是它以错误的比例绘制图像。 我正在使用自定义比例监听器根据建议here缩放画布：

public class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

    private float lastFocusX;
    private float lastFocusY;

    public ScaleListener() {
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        lastFocusX = detector.getFocusX();
        lastFocusY = detector.getFocusY();
        return true;
    }

    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        Matrix transformatioMatrix = new Matrix();
        float focusX = detector.getFocusX();
        float focusY = detector.getFocusY();

        transformatioMatrix.postTranslate(-focusX, -focusY);
        transformatioMatrix.postScale(detector.getScaleFactor(), detector.getScaleFactor());

        float focusShiftX = focusX - lastFocusX;
        float focusShiftY = focusY - lastFocusY;
        transformatioMatrix.postTranslate(focusX + focusShiftX, focusY + focusShiftY);

        backgroundMatrix.postConcat(transformatioMatrix);

        lastFocusX = focusX;
        lastFocusY = focusY;

        return true;
    }
}

和SimpleOnGestureListener滚动并绘制图像

public class ScrollListener extends GestureDetector.SimpleOnGestureListener{
    @Override
    public boolean onSingleTapConfirmed(MotionEvent e) {
        return true;
    }

    @Override
    public boolean onSingleTapUp(MotionEvent event) {           
        float touchX = event.getX();
        float touchY = event.getY();
        Toast.makeText(context, "onSingleTapUp", Toast.LENGTH_SHORT).show();
        playersCanvas.drawBitmap(playerBitmap, touchX, touchY, canvasPaint);
        invalidate();
        return true;
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
            float distanceX, float distanceY) {
        backgroundMatrix.postTranslate(-distanceX, -distanceY);
        invalidate();
        return true;
    }
}

这是我的OnDraw：

@Override
protected void onDraw(Canvas canvas) {  
    canvas.drawBitmap(background, backgroundMatrix, canvasPaint);
    canvas.drawBitmap(playersBitmap, backgroundMatrix, canvasPaint);
}

现在，当我触摸屏幕时，图像确实会绘制到画布，但不是我触摸的位置，而不是正确的比例。 例如： 这是原始背景：

在缩放和滚动后，我触摸了红色圆圈位置的屏幕（之后添加），图像绘制在右下角

缩小回原始大小后，您可以在画布上看到错误的位置：

我发现this线程假设我有比例点，我不会因为“免费”比例和滚动选项。

如何以正确的比例在正确的位置绘制图像？

Answer 1

通过@pskink提示找到答案。现在onSingleTapUp看起来像这样：

        @Override
    public boolean onSingleTapUp(MotionEvent event) {           
        float touchX = event.getX();
        float touchY = event.getY();

        float[] points = new float[2];          
        points[0] = touchX;
        points[1] = touchY;

        Matrix inverse = new Matrix();
        backgroundMatrix.invert(inverse);
        inverse.mapPoints(points);
        Bitmap scaledPlayer = Bitmap.createBitmap(playerBitmap, 0, 0, playerBitmap.getWidth(), playerBitmap.getHeight(), inverse, true);
        playersCanvas.drawBitmap(scaledPlayer, points[0], points[1], canvasPaint);

        invalidate();
        return true;
    }