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Hit detection using CGContextPathContainsPoint
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Hit detection using CGContextPathContainsPoint

Hi everybody,

On page 94, Apple's latest "Cocoa Drawing Guide" gives an example on how to perform hit a mouse hit detection on a stroked path using CGContextPathContainsPoint.

- (BOOL)pathContainsPoint:(NSPoint)point forMode:(CGPathDrawingMode)mode
{
CGPathRef path = [self quartzPath]; // Custom method to create a CGPath
CGContextRef cgContext = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
CGPoint cgPoint;
BOOL containsPoint = NO;

    cgPoint.x = point.x;
    cgPoint.y = point.y;

    // Save the graphics state before doing the hit detection.
    CGContextSaveGState(cgContext);

CGContextAddPath(cgContext, path);
containsPoint = CGContextPathContainsPoint(cgContext, cgPoint, mode);

    CGContextRestoreGState(cgContext);

    return containsPoint;
}

What I currently don't understand is how to provide a valid CGContext during the mouseDown: event phase in which the hit detection has to be performed. The [[NSGraphicsContext currentContext] graphicsPort] which is used in the example is only valid during the drawing phase.

Has anybody an idea how this could work? Is it sensible to create a temporary PDF/Bitmap context just for detecting hits?

Cheers

Frank

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