android 在画布上缩放和变换的图像上绘制线

Question

我在画布上缩放和变换后的图像上绘制线条时遇到问题，对于变换后的图像，我可以在图像上绘制线条，但如果图像缩放（放大或缩小），则使用手指触摸意外绘制线条像素。由于我正在研究绘画应用程序，但对此没有更多的了解，所以我需要您的帮助，我在谷歌上搜索了它，但没有运气，我

在这里没有找到任何东西，第一张图像默认工作正常，在第二个移动图像工作正常，正确绘制了线条

而在第三个缩放图像上无法正确绘制，我的意思是如果从左上角/左上角开始绘制，则绘制的线点会有所不同，如下所示

如果您需要代码，请说出来，我将编辑问题

Answer 1

好吧，经过多次实施，我得到了解决方案。

这是我在 onDraw() 中绘图的代码，

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.save();
    canvas.translate(mPosX, mPosY);
    canvas.scale(mScaleFactor, mScaleFactor);

    canvas.drawBitmap(MoveImageTestActivity.bmp, 0,0,null);
    if(mScaleFactor!=1.f)
        canvas.restore();

    if(isDrawing)
        canvas.drawPath(tempPath,get_paint());

    if(mScaleFactor==1.f)
        canvas.restore();
}

在这里您必须检查比例因子值以恢复画布。如果比例因子值默认为 1.f 并且图像刚刚移动，则在绘制线/路径后恢复，如果比例因子不等于 1.f（默认），则首先恢复画布，然后绘制线/使用手指触摸绘制时的路径。

这是我的 onTouch() 代码

@Override
public boolean onTouchEvent(MotionEvent ev) {
    mScaleDetector.onTouchEvent(ev);
    final int action = ev.getAction();
    switch (action & MotionEvent.ACTION_MASK) {
    case MotionEvent.ACTION_DOWN: {
        final float x = ev.getX();
        final float y = ev.getY();

        if(isDrawing){
            float dx = ev.getX();
            float dy = ev.getY();;

            if(mScaleFactor==1.f){
                dx = ev.getX() - mPosX;
                dy = ev.getY() - mPosY;
            }
            tempPath = new Path();
            tempPath.moveTo(dx,dy);
        }else{
            mLastTouchX = x;
            mLastTouchY = y;
            // Save the ID of this pointer
            mActivePointerId = ev.getPointerId(0);
        }
        break;
    }

    case MotionEvent.ACTION_MOVE: {
        // Find the index of the active pointer and fetch its position
        if(isDrawing){
            float dx = ev.getX();
            float dy = ev.getY();;

            if(mScaleFactor==1.f){
                dx = ev.getX() - mPosX;
                dy = ev.getY() - mPosY;
            }
            tempPath.lineTo(dx,dy);
        }else{
            final int pointerIndex = ev.findPointerIndex(mActivePointerId);
            final float x = ev.getX(pointerIndex);
            final float y = ev.getY(pointerIndex);

            final float dx = x - mLastTouchX;
            final float dy = y - mLastTouchY;

            mPosX += dx;
            mPosY += dy;

            mLastTouchX = x;
            mLastTouchY = y;
        }
        break;
    }
    case MotionEvent.ACTION_UP: {
        points.clear();
        mActivePointerId = INVALID_POINTER_ID;
        break;
    }

    case MotionEvent.ACTION_CANCEL: {
        mActivePointerId = INVALID_POINTER_ID;
        break;
    }

    case MotionEvent.ACTION_POINTER_UP: {
        if(!isDrawing){
            // Extract the index of the pointer that left the touch sensor
            final int pointerIndex = (action & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
            final int pointerId = ev.getPointerId(pointerIndex);
            if (pointerId == mActivePointerId) {
                // This was our active pointer going up. Choose a new
                // active pointer and adjust accordingly.
                final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                mLastTouchX = ev.getX(newPointerIndex);
                mLastTouchY = ev.getY(newPointerIndex);
                mActivePointerId = ev.getPointerId(newPointerIndex);
            }
        }
        break;
    }
    }
    invalidate();
    return true;
}