Tengo un pequeño problema con mi aplicación. Acabo de implementar el zoom de pellizco, pero cuando pellizco para ampliar, la imagen no se escala en el centro de los 2 puntos como se muestra en las imágenes de abajo. La imagen 1 es donde están mis dedos antes de pellizcar y la imagen 2 es para mostrar que no se ha escalado en el centro de mis dedos como debería.

Imagen 1 vs Imagen 2:

Aquí está mi código:

        package com.jpiionefourone.guitarimage;

    import android.content.Context;
    import android.graphics.Canvas;
    import android.graphics.drawable.Drawable;
    import android.util.AttributeSet;
    import android.view.MotionEvent;
    import android.view.ScaleGestureDetector;
    import android.view.View;

    public class MultiTouchView extends View {
        private Drawable mIcon;
        private float mPosX;
        private float mPosY;

        private float mLastTouchX;
        private float mLastTouchY;

        private static final int INVALID_POINTER_ID = -1;

        // The ‘active pointer’ is the one currently moving our object.
        private int mActivePointerId = INVALID_POINTER_ID;

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


        public MultiTouchView(Context context) {
            this(context, null, 0);
        }

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

        public MultiTouchView(Context context, AttributeSet attrs, int defStyle) {
            super(context, attrs, defStyle);
            mIcon = context.getResources().getDrawable(R.drawable.guitar);
            mIcon.setBounds(0, 0, mIcon.getIntrinsicWidth(), mIcon.getIntrinsicHeight());

            // Create our ScaleGestureDetector
            mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());

        }

        @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;
            }
            }

            return true;
        }

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

            canvas.save();
            canvas.translate(mPosX, mPosY);
            canvas.scale(mScaleFactor, mScaleFactor);
            mIcon.draw(canvas);
            canvas.restore();
        }

        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;
            }
        }
    }

Gracias,

Jared