start and end angle of UIBezierPath?

Question

I have coded as below for half circle in iOS using UIBezierPath and CAShapeLayer.

 clockWiseLayer = [[CAShapeLayer alloc] init]         


        

Answer 1

Check documentation for coordinates: http://i.stack.imgur.com/1yJo6.png

Y-Axis is reversed compared to standard coordinate system in mathematics.

You should draw from 1/2*PI (bottom anchor) to 3/2*PI (top anchor) and then you set strokeStart to 0.0f and strokeEnd to 1.0f (so it fills whole path).

Working code using iOS constants:

CGFloat startAngle = M_PI_2;
CGFloat endAngle = startAngle + M_PI;
CGFloat width = CGRectGetWidth(imageView.frame)/2.0f;
CGFloat height = CGRectGetHeight(imageView.frame)/2.0f;
CGPoint centerPoint = CGPointMake(width, height);
float radius = CGRectGetWidth(imageView.frame)/2+10;
CAShapeLayer* clockWiseLayer = [[CAShapeLayer alloc] init];
clockWiseLayer.path = [UIBezierPath bezierPathWithArcCenter:centerPoint
                                                     radius:radius
                                                 startAngle:startAngle
                                                   endAngle:endAngle
                                                  clockwise:YES].CGPath;

clockWiseLayer.fillColor = [UIColor clearColor].CGColor;
clockWiseLayer.strokeColor = [UIColor blueColor].CGColor;
clockWiseLayer.borderColor = [UIColor greenColor].CGColor;
clockWiseLayer.backgroundColor = [UIColor redColor].CGColor;

clockWiseLayer.strokeStart = 0.0f;
clockWiseLayer.strokeEnd = 1.0f;

clockWiseLayer.lineWidth = 2.0f;
clockWiseLayer.borderWidth = 5.0f;
[self.layer addSublayer:clockWiseLayer];