在android中放大/缩小或拖动后获取Canvas坐标 [英] Get Canvas coordinates after scaling up/down or dragging in android

问题描述

我正在开发一个应用程序，我可以在其中粘贴图像、在画布上进行绘图和绘画.此应用程序还可以放大/缩小画布或将其拖动到不同的位置.我的问题是:缩放或拖动画布后我无法获得正确的画布坐标.我想在画布被缩放或拖动后绘制手指画，但无法检索到我触摸过的正确位置..:(另外我是新蜜蜂.这是代码.

I'm developing an application in which I'm pasting images, doing drawing and painting on canvas. This app can also Scale up/down the canvas or drag it to different location. My problem is: I can't get the correct canvas coordinates after scaling or dragging the canvas. I want to draw finger paint after the canvas is scaled or dragged but unable to retrieve the right place where i've touched..:( Also I'm new bee. Here is the code.

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

    canvas.save();
    //canvas.translate(mPosX, mPosY);
    canvas.scale(mScaleFactor, mScaleFactor, super.getWidth() * 0.5f,
            super.getHeight() * 0.5f);
    mIcon.draw(canvas);
    for (Path path : listPath) {
        canvas.drawPath(path, paint);
    }
    canvas.restore();
}

public TouchExampleView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    // Let the ScaleGestureDetector inspect all events.
    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();

        mLastTouchX = x;
        mLastTouchY = y;
        mActivePointerId = ev.getPointerId(0);
        break;
    }

    case MotionEvent.ACTION_MOVE: {
        final int pointerIndex = ev.findPointerIndex(mActivePointerId);
        final float x = ev.getX(pointerIndex);
        final float y = ev.getY(pointerIndex);

        // Only move if the ScaleGestureDetector isn't processing a gesture.
        if (!mScaleDetector.isInProgress()) {
            final float dx = x - mLastTouchX;
            final float dy = y - mLastTouchY;

            mPosX += dx;
            mPosY += dy;

            invalidate();
        }

        mLastTouchX = x;
        mLastTouchY = y;

        break;
    }

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

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

    case MotionEvent.ACTION_POINTER_UP: {
        final int pointerIndex = (ev.getAction() & 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;
    }
    }

    float objectNewX,objectNewY;
    if (mScaleFactor >= 1) {
        objectNewX = ev.getX() + (ev.getX() - super.getWidth() * 0.5f) * (mScaleFactor - 1);
        objectNewY = ev.getY() + (ev.getY() - super.getHeight() * 0.5f) * (mScaleFactor - 1);
    } else {
        objectNewX = ev.getX() - (ev.getX() - super.getWidth() * 0.5f) * (1 - mScaleFactor);
        objectNewY = ev.getY() - (ev.getY() - super.getHeight() * 0.5f) * (1 - mScaleFactor);
    }

    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        path = new Path();
        path.moveTo(objectNewX,objectNewY);
        path.lineTo(objectNewX,objectNewY);
    } else if (ev.getAction() == MotionEvent.ACTION_MOVE) {
        path.lineTo(objectNewX,objectNewY);
        listPath.add(path);
    } else if (ev.getAction() == MotionEvent.ACTION_UP) {
        path.lineTo(objectNewX,objectNewY);
        listPath.add(path);
    }

    return true;
}

private class ScaleListener extends
        ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        mScaleFactor *= detector.getScaleFactor();

        // Don't let the object get too small or too large.
        mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f));

        invalidate();
        return true;
    }
}

推荐答案

终于自己搞定了.

通过将此公式应用于 (px,py) 坐标来绘制所有内容:

Draw everything by applying this formula to (px,py) coordinates:

float px = ev.getX() / mScaleFactor + rect.left;
float py = ev.getY() / mScaleFactor + rect.top;
rect = canvas.getClipBounds();
//Get them in on Draw function and apply above formula before drawing

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