Question

I am making a CGPoint and a CGPathRef then trying to find if the CGPoint is inside the CGPathRef. Here is the code:

CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, NULL, 0, 0);
CGPathMoveToPoint(path, NULL, 200, 0);
CGPathMoveToPoint(path, NULL, 200, 200);
CGPathMoveToPoint(path, NULL, 0, 200);
CGPathCloseSubpath(path);

CGPoint hitPoint = CGPointMake(77, 77);

if ( CGPathIsEmpty(path) )
    NSLog(@"Path Is Empty!");
else
{
    if ( CGPathIsRect(path, NULL) ) 
        NSLog(@"Path is a Rectangle!");
    else
    {
        NSLog(@"Path is NOT a Rectangle!");
        if (CGPathContainsPoint(path, NULL, hitPoint, FALSE)) // FALSE or TRUE - same result
            NSLog(@"Hit Point Inside: x=%f, y=%f", hitPoint.x, hitPoint.y);
        else
            NSLog(@"Hit Point Outside: x=%f, y=%f", hitPoint.x, hitPoint.y);
    }
}    

The output reads:

Path is NOT a Rectangle!
Hit Point Outside: x=77.000000, y=77.000000

The path obviously is a rectangle and the point is inside the closed path. Please clue me in on what I am doing wrong here.

Answer 1

CGRectIsPath only returns true if the path was created by CGPathCreateWithRect (with a transform parameter that doesn’t rotate or skew the rectangle), or if the path was created by CGPathCreateMutable and had a single rectangle added to it with CGPathAddRect.

It would be much more work for it to figure out whether any arbitrary path is exactly a rectangle. The path might contain bezier curve segments that are actually straight lines, or sides that are built from consecutive straight line segments.

If you need to detect whether any arbitrary path is actually just a rectangle, you will have to do it yourself using CGPathApply. It will be complicated.

As for why your point-inside test isn’t working: you need to use CGPathAddLineToPoint to create the sides of your rectangle:

CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, NULL, 0, 0);
CGPathAddLineToPoint(path, NULL, 200, 0);
CGPathAddLineToPoint(path, NULL, 200, 200);
CGPathAddLineToPoint(path, NULL, 0, 200);
CGPathCloseSubpath(path);