问如何计算Android缩放画布的坐标

EN

public class Painter extends View {

    //
    private static final int INVALID_POINTER_ID = -1;
    private float mPosX;
    private float mPosY;

    private float mLastTouchX;
    private float mLastTouchY;
    private int mActivePointerId = INVALID_POINTER_ID;

    private ScaleGestureDetector mScaleDetector;
    private float mScaleFactor = 1.f;
    //

    Paint paint = new Paint();

    List<Table> printTable = new ArrayList<Table>(); // lista wyświetlanych stolików

    //
    List<Pointer> listPointer = new ArrayList<Pointer>();
    //

    public Painter(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public Painter(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
    }

    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, 10.0f));

            invalidate();
            return true;
        }
    }

    @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);
            for(int i = 0; i<listPointer.size(); i++)
            {
                if(listPointer.get(i).getRectangle().contains((int)(Math.round(x)), (int)(Math.round(y))))
                {
                    if(listPointer.get(i).getIsItTable())
                    {
                        Log.e("Exc", "Stolik "+listPointer.get(i).getId());
                    }
                    else
                    {
                        Log.e("Exc", "Button "+listPointer.get(i).getId());
                    }
                }
            }
            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;
        }
        }

        return true;
    }

    //

    public Painter(Context context) {

        this(context, null, 0);

        paint.setColor(Color.BLACK);

        List<Table> printTable = Bridge.getTables(getContext()); 

    }

    @SuppressLint("DrawAllocation")
    @Override
    public void onDraw(Canvas canvas) {

        super.onDraw(canvas);
            Rect rect = null;
            RectF rectF = null;
            // czyszczenie tablicy
            listPointer.clear();

            for(int j = 0; j<printTable.size(); j++)
            {
                Table item = printTable.get(j);
                // Obsługa rozciągania

                canvas.save();
                Log.d("DEBUG", "X: "+mPosX+" Y: "+mPosY);
                canvas.translate(mPosX, mPosY);
                canvas.scale(mScaleFactor, mScaleFactor);

                // dodaje do tablicy stołów
                paint.setColor(getResources().getColor(R.color.green));
                rect = new Rect(item.getX1(), item.getY1(), item.getX2(), item.getY2());
                rectF = new RectF(rect);
                canvas.drawRoundRect(rectF, 0,0, paint);
                listPointer.add(new Pointer(rect, true, j));

                canvas.restore();
            }
    }