Changing the layer shape for CPTPlotSpaceAnnotation?

问题

I want to add a widget to my graph that a user can click and drag. I've managed to do this using CPTPlotSpaceAnnonation (because I also want it to also scroll with the data) and CPTBorderedLayer. The basic functionality works and now I want to improve the look of the widget. So far it's just a green circle.

The follow code generates the circle below, notice how the shadow is clipped to the rect of the layer and the border follows the layer and not the circle,

How can I stroke the circle and not the layer? I guess I can avoid clipping by making the frame of the layer larger. Is possible to use CAShapeLayer class with the Core Plot annotations? This would be an easy way of drawing the widgets.

// Add a circular annotation to graph with fill and shadow
annotation = [[CPTPlotSpaceAnnotation alloc] 
                  initWithPlotSpace:graph.defaultPlotSpace 
                    anchorPlotPoint:anchorPoint];

// Choosing line styles and fill for the widget
NSRect frame = NSMakeRect(0, 0, 50.0, 50.0);
CPTBorderedLayer *borderedLayer = [[CPTBorderedLayer alloc] initWithFrame:frame];

// Circular shape with green fill
CGPathRef outerPath = CGPathCreateWithEllipseInRect(frame, NULL);
borderedLayer.outerBorderPath = outerPath;
CPTFill *fill = [CPTFill fillWithColor:[CPTColor greenColor]];
borderedLayer.fill = fill;

// Basic shadow
CPTMutableShadow *shadow = [CPTMutableShadow shadow];
shadow.shadowOffset = CGSizeMake(0.0, 0.0);
shadow.shadowBlurRadius = 6.0;
shadow.shadowColor = [[CPTColor blackColor] colorWithAlphaComponent:1.0];
borderedLayer.shadow = shadow;

// Add to graph
annotation.contentLayer = borderedLayer;
annotation.contentLayer.opacity = 1.0;
[graph addAnnotation:annotation];

回答1:

Don't set the border paths of the layer. Instead, just set the cornerRadius to half the width of the frame.

borderedLayer.cornerRadius = frame.size.width * 0.5;

来源：https://stackoverflow.com/questions/11588862/changing-the-layer-shape-for-cptplotspaceannotation