Android-Pinch缩放触摸事件坐标

我正在尝试获取我正在创建的android应用程序的画布坐标。在我添加代码以使用缩放焦点（以下两行）之前，它工作得非常好：

以下是我的视图类的源代码：

    package us.kniffin.Jigsaw;

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.view.GestureDetector.SimpleOnGestureListener;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;

public class TestView extends View {
    private float mLastTouchX;
    private float mLastTouchY;
    private float mPosX;
    private float mPosY;

    private Rect rect;

    private float cX, cY; // circle coords


    // Scaling objects
    private ScaleGestureDetector mScaleDetector;
    private float mScaleFactor = 1.f;
    // The focus point for the scaling
    private float scalePointX; 
    private float scalePointY;


    public TestView(Context context) {
        super(context);

        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
    }

    @Override
    protected void onDraw(Canvas canvas) {      
        super.onDraw(canvas);
        Paint p = new Paint();
        p.setColor(Color.RED);

         rect = canvas.getClipBounds();

        canvas.save();
        canvas.scale(mScaleFactor, mScaleFactor, scalePointX, scalePointY);
        canvas.translate(mPosX, mPosY);
        canvas.drawCircle(cX, cY, 10, p);

        canvas.restore();

    }

    @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()/mScaleFactor;// screen X position
            final float y = ev.getY()/mScaleFactor;// screen Y position

            cX = x - (rect.left * mScaleFactor) - mPosX; // canvas X
            cY = y - (rect.top * mScaleFactor) - mPosY; // canvas Y

            // Remember where we started
            mLastTouchX = x;
            mLastTouchY = y;
            break;
        }
        case MotionEvent.ACTION_MOVE: {
            final float x = ev.getX()/mScaleFactor;
            final float y = ev.getY()/mScaleFactor;
            cX = x - (rect.left * mScaleFactor) - mPosX; // canvas X
            cY = y - (rect.top * mScaleFactor) - mPosY; // canvas Y


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

                mPosX += dx;
                mPosY += dy;

                invalidate();
            }

            mLastTouchX = x;
            mLastTouchY = y;

            break;

        }
        case MotionEvent.ACTION_UP: {
            mLastTouchX = 0;
            mLastTouchY = 0;
            invalidate();
        }
        }
        return true;
    }

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

            // Don't let the object get too small or too large.
            mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));

            invalidate();
            return true;
        }
    }


}

你知道我需要做些什么来让它工作吗

更新：我将代码示例替换为另一个具有相同问题的代码示例，但已简化为要点

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再次更新：缩放后出现问题。缩放前，坐标是正确的，但缩放后，坐标离单击位置的右侧和下方太远。看起来，缩小的越多，错误就越大。

无论何时使用平移、缩放、旋转（等），都会更改画布的矩阵。 通常，此矩阵用于告诉您每个（x，y）在画布上的位置。 创建画布时，矩阵为标识矩阵： (1 ) ( 1 ) ( 1) 但只要你做了这些改变，这个矩阵也会改变。

---

如果你想知道正确的坐标，那么在缩放/旋转之前，你应该使用canvas.save（），缩放之后使用canvas.restore（）

哈哈！成功！这几乎花了我一整天的时间，但我通过一大堆猜测和检查才弄明白

以下是我需要的代码：

case MotionEvent.ACTION_DOWN: {
            final float x = (ev.getX() - scalePointX)/mScaleFactor;
            final float y = (ev.getY() - scalePointY)/mScaleFactor;
            cX = x - mPosX + scalePointX; // canvas X
            cY = y - mPosY + scalePointY; // canvas Y
[snip]
}

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我最近在做一些非常类似的事情时遇到了这个问题，经过反复尝试和大量的谷歌搜索，我最终修改了这个答案（）：

（e是一个MotionEvent，因此最好在onTouch或onLongPress中使用此代码）

---

这里可以应用一些明显的优化，但我认为这样做更清楚。

如果你能制作一个更小的程序来展示同样的效果，你可能更容易得到答案。祝你好运好建议。我会的。另一个建议是：你应该解释到底发生了什么，比如你得到了什么坐标（或错误），如果它们总是偏离100或总是到大/小/随机/，为什么你要缩放以及那些可能有用的东西好吧，我也更新了。有什么建议吗？好的。我正在使用“保存和还原”，但这无助于解决我的问题。我不太明白。我用错了吗？哇，我的朋友很感激你的努力。

case MotionEvent.ACTION_DOWN: {
            final float x = (ev.getX() - scalePointX)/mScaleFactor;
            final float y = (ev.getY() - scalePointY)/mScaleFactor;
            cX = x - mPosX + scalePointX; // canvas X
            cY = y - mPosY + scalePointY; // canvas Y
[snip]
}

mClickCoords = new float[2];

//e is the motionevent that contains the screen touch we
//want to translate into a canvas coordinate
mClickCoords[0] = e.getX();
mClickCoords[1] = e.getY();

Matrix matrix = new Matrix();
matrix.set(getMatrix());

//this is where you apply any translations/scaling/rotation etc.
//Typically you want to apply the same adjustments that you apply
//in your onDraw().

matrix.preTranslate(mVirtualX, mVirtualY);
matrix.preScale(mScaleFactor, mScaleFactor, mPivotX, mPivotY);

// invert the matrix, creating the mapping from screen 
//coordinates to canvas coordinates
matrix.invert(matrix); 

//apply the mapping
matrix.mapPoints(mClickCoords);

//mClickCoords[0] is the canvas x coordinate and
//mClickCoords[1] is the y coordinate.