GLKMathUnproject : detecting a tap on an object

Question

So, it seems that GLKit has GLKMathUnproject which can be used to work out where you clicked in 3D space (awesome)

However, I cant get it to work, I have copied a few different examples in and it still does not detect me clicking on my cube at 0,0,0. I basically do a for next loop and see if my ray hits my cube.

-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSSet* allTouches = [event allTouches];
    UITouch*touch1 = [[allTouches allObjects] objectAtIndex:0];
    CGPoint touch1Point = [touch1 locationInView:self.view];


    GLKVector3 window_coord = GLKVector3Make(touch1Point.x,touch1Point.y, 0.0f);
    bool result;

    GLint viewport[4] = {};
    glGetIntegerv(GL_VIEWPORT, viewport);

    GLKVector3 near_pt = GLKMathUnproject(window_coord, _baseModelViewMatrix, _projectionMatrix, &viewport[0], &result);

    window_coord = GLKVector3Make(touch1Point.x,touch1Point.y, 1.0f);

    GLKVector3 far_pt = GLKMathUnproject(window_coord, _baseModelViewMatrix, _projectionMatrix, &viewport[0], &result);

    //need to get z=0 from
    //assumes near and far are on opposite sides of z=0
    float z_magnitude = fabs(far_pt.z-near_pt.z);
    float near_pt_factor = fabs(near_pt.z)/z_magnitude;
    float far_pt_factor = fabs(far_pt.z)/z_magnitude;

    GLKVector3 final_pt = GLKVector3Add( GLKVector3MultiplyScalar(near_pt, far_pt_factor), GLKVector3MultiplyScalar(far_pt, near_pt_factor));


    float xDif = (final_pt.x - near_pt.x) / 1000;
    float yDif = (final_pt.y - near_pt.y) / 1000;
    float zDif = (final_pt.z - near_pt.z) / 1000;

    for (int i = 0; i < 100; i ++)
    {
        if ((near_pt.x + (xDif * i)) > self.cube.position.x - self.cube.scale.x && (near_pt.x + (xDif * i)) < self.cube.position.x + self.cube.scale.x &&
            (near_pt.y + (yDif * i)) > self.cube.position.y - self.cube.scale.y && (near_pt.y + (yDif * i)) < self.cube.position.y + self.cube.scale.y &&
            (near_pt.z + (zDif * i)) > self.cube.position.z - self.cube.scale.z && (near_pt.z + (zDif * i)) < self.cube.position.z + self.cube.scale.z)
        {
            NSLog(@"%f %f %f", final_pt.x, final_pt.y, final_pt.z);
            NSLog(@"Hit cube");
        }

    }

}

Answer 1

I found the answer here Updating OpenGL ES Touch Detection (Ray Tracing) for iPad Retina?

- (void)handleTap: (UITapGestureRecognizer *)recognizer
{

    CGPoint tapLoc = [recognizer locationInView:self.view];
    tapLoc.x *= [UIScreen mainScreen].scale;
    tapLoc.y *= [UIScreen mainScreen].scale;

    bool testResult;

    GLint viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);

    float uiKitOffset = 113; //Need to factor in the height of the nav bar + the height of the tab bar at the bottom in the storyboard.

    GLKVector3 nearPt = GLKMathUnproject(GLKVector3Make(tapLoc.x, (tapLoc.y-viewport[3]+uiKitOffset)*-1, 0.0), modelViewMatrix, projectionMatrix, &viewport[0] , &testResult);

    GLKVector3 farPt = GLKMathUnproject(GLKVector3Make(tapLoc.x, (tapLoc.y-viewport[3]+uiKitOffset)*-1, 1.0), modelViewMatrix, projectionMatrix, &viewport[0] , &testResult);

    farPt = GLKVector3Subtract(farPt, nearPt);

    ....
}