How to draw an elliptical arc with CoreGraphics?

Question

Is it possible to draw an elliptical arc like SVG path, in CoreGraphics and how?

Answer 1

I ran into the same thing tonight. CG doesn't offer an easy way to draw a non-circular arc, but you can do it using CGPath and a suitable transformation matrix. Suppose you want an arc of an axis-aligned ellipse starting at left,top and with a size of width,height. Then you can do something like this:

CGFloat cx = left + width*0.5;
CGFloat cy = top + height*0.5;
CGFloat r = width*0.5;

CGMutablePathRef path = CGPathCreateMutable();
CGAffineTransform t = CGAffineTransformMakeTranslation(cx, cy);
t = CGAffineTransformConcat(CGAffineTransformMakeScale(1.0, height/width), t);
CGPathAddArc(path, &t, 0, 0, r, startAngle, endAngle, false);
CGContextAddPath(g->cg, path);

CGContextStrokePath(g);

CFRelease(path);

Note that if you want to draw a pie-shaped wedge, then just surround the "CGContextAddPath" call with a CGContextMoveToPoint(cx,cy) and a CGContextAddLineToPoint(cx,cy), and use CGContextFillPath instead of CGContextStrokePath. (Or if you want to fill and stroke at the same time, use CGContextDrawPath.)