Question

How do I implement pinch to zoom to a parallax scrolling node?

Answer 1

Here’s the solution:

- (void)handlePitchZoom:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch* touch1 = [[[event allTouches] allObjects] objectAtIndex:0];
    UITouch* touch2 = [[[event allTouches] allObjects] objectAtIndex:1];

    // calculate scale value
    double prevDistance = ccpDistance([touch1 previousLocationInView:[touch1 view]], [touch2 previousLocationInView:[touch2 view]]);
    double newDistance  = ccpDistance([touch1 locationInView:[touch1 view]], [touch2 locationInView:[touch2 view]]); 

    CGFloat relation = newDistance / prevDistance;
    CGFloat newScale = self.scale * relation;

    if ((newScale >= minScale) && (newScale <= maxScale)) {

        CGPoint touch1Location = [parallaxNode convertTouchToNodeSpace:touch1];
        CGPoint touch2Location = [parallaxNode convertTouchToNodeSpace:touch2];

        // calculate center point between two touches
        CGPoint centerPoint = ccpMidpoint(touch1Location, touch2Location);

        // store center point location (ScrollableView space)
        CGPoint centerPointInParentNodeSpace = [self convertPoint:centerPoint fromNode:parallaxNode];
        CGPoint oldPoint = ccp(centerPointInParentNodeSpace.x * (self.scale), centerPointInParentNodeSpace.y * (self.scale));
        self.scale = newScale;

        CGPoint newPoint = ccp(centerPointInParentNodeSpace.x * (self.scale), centerPointInParentNodeSpace.y * (self.scale));
        CGPoint diff = ccp(oldPoint.x - newPoint.x , oldPoint.y - newPoint.y);

        [parallaxNode setPosition:ccp(parallaxNode.position.x + (diff.x*(1/self.scale)), parallaxNode.position.y + (diff.y*(1/self.scale)))];
    }

Hope it will help someone…