Objective-C Draw a Circle with a Ring shape - objective-c

Question

I wrote this class that draws a animated progress with a circle (it draws a circular sector based on a float progress)
#implementation MXMProgressView
#synthesize progress;
- (id)initWithDefaultSize {
int circleOffset = 45.0f;
self = [super initWithFrame:CGRectMake(0.0f,
0.0f,
135.0f + circleOffset,
135.0f + circleOffset)];
self.backgroundColor = [UIColor clearColor];
return self;
}
- (void)drawRect:(CGRect)rect {
CGRect allRect = self.bounds;
CGRect circleRect = CGRectMake(allRect.origin.x + 2, allRect.origin.y + 2, allRect.size.width - 4,
allRect.size.height - 4);
CGContextRef context = UIGraphicsGetCurrentContext();
// background image
//UIImage *image = [UIImage imageNamed:#"loader_disc_hover.png"];
//[image drawInRect:circleRect];
// Orange: E27006
CGContextSetRGBFillColor(context,
((CGFloat)0xE2/(CGFloat)0xFF),
((CGFloat)0x70/(CGFloat)0xFF),
((CGFloat)0x06/(CGFloat)0xFF),
0.01f); // fill
//CGContextSetLineWidth(context, 2.0);
CGContextFillEllipseInRect(context, circleRect);
//CGContextStrokeEllipseInRect(context, circleRect);
// Draw progress
float x = (allRect.size.width / 2);
float y = (allRect.size.height / 2);
// Orange: E27006
CGContextSetRGBFillColor(context,
((CGFloat)0xE2/(CGFloat)0xFF),
((CGFloat)0x70/(CGFloat)0xFF),
((CGFloat)0x06/(CGFloat)0xFF),
1.0f); // progress
CGContextMoveToPoint(context, x, y);
CGContextAddArc(context, x, y, (allRect.size.width - 4) / 2, -M_PI_2, (self.progress * 2 * M_PI) - M_PI_2, 0);
CGContextClosePath(context);
CGContextFillPath(context);
}
#end
Now what I want to do I to draw a ring shape with the same progress animation, instead of filling the full circle, so a circular sector again not starting from the center of the circle.
I tried with CGContextAddEllipseInRect and the CGContextEOFillPath(context);
with no success.

Answer 1

I think you'll need to construct a more complex path, something like:
// Move to start point of outer arc (which might not be required)
CGContextMoveToPoint(context, x+outerRadius*cos(startAngle), y+outerRadius*sin(startAngle));
// Add outer arc to path (counterclockwise)
CGContextAddArc(context, x, y, outerRadius, startAngle, endAngle, 0);
// move *inward* to start point of inner arc
CGContextMoveToPoint(context, x+innerRadius*cos(endAngle), y+innerRadius*sin(endAngle));
// Add inner arc to path (clockwise)
CGContextAddArc(context, x, y, innerRadius, endAngle, StartAngle, 1);
// Close the path from end of inner arc to start of outer arc
CGContextClosePath(context);
Note: I haven't tried the above code myself

Answer 2

Cheap and nasty solution:
Draw a solid circle that is smaller than the original circle by the thickness of the ring you want to draw.
Draw this circle on top of the original circle, all that you will see animating is the ring.