Question

I’ve got an array of CALayers containing images which can be moved around by the user, and i’m trying to use containsPoint to detect if they have been touched – the code is as follows:

int num_objects = [pageImages count];

lastTouch = [touch locationInView:self];

CGRect objRect;
CALayer *objLayer;

for (int i = 0; i < num_objects; i++) {

    objLayer = [pageImages objectAtIndex:i];
    objRect = objLayer.bounds;

    NSLog(@"layerPos:%@, layerBounds:%@", NSStringFromCGPoint(objLayer.position), NSStringFromCGRect(objRect));
    NSLog(@"point:%@", NSStringFromCGPoint(lastTouch));

    if ([objLayer containsPoint:lastTouch] == TRUE) {
        NSLog(@"touched object %d", i);
        return i;
    }
}

The information i’m outputting puts the touch within the bounds of the layer (i’ve assumed position is the centre of the layer, i haven’t altered the anchor point. The layer hasn’t been rotated or anything like that either), but containsPoint: doesn’t return true. Can anyone see what i’m doing wrong, or suggest a different/better way to achieve what i want?

Answer 1

So .. found the problem – the point needs to be converted from superlayer coordinates in order to work with the layer containsPoint:

replace

if ([objLayer containsPoint:lastTouch] == TRUE) {

with

if ([objLayer containsPoint:[objLayer convertPoint:lastTouch fromLayer:objLayer.superlayer]] == TRUE) {

You can mess about with the co-ordinates yourself and use CGRectContainsPoint: (see comments above), but this is a simpler solution so i get to answer my own question for the first time. big tick for me, yay!