How to draw stars using Quartz Core?

Question

I\'m trying to adapt an example provided by Apple in order to programmatically draw stars in line, the code is the following:

CGContextRef context = UIGraphi         


        

Answer 1

Here's an algorithm to implement what buddhabrot implied:

- (void)drawStarInContext:(CGContextRef)context withNumberOfPoints:(NSInteger)points center:(CGPoint)center innerRadius:(CGFloat)innerRadius outerRadius:(CGFloat)outerRadius fillColor:(UIColor *)fill strokeColor:(UIColor *)stroke strokeWidth:(CGFloat)strokeWidth {
    CGFloat arcPerPoint = 2.0f * M_PI / points;
    CGFloat theta = M_PI / 2.0f;

    // Move to starting point (tip at 90 degrees on outside of star)
    CGPoint pt = CGPointMake(center.x - (outerRadius * cosf(theta)), center.y - (outerRadius * sinf(theta)));
    CGContextMoveToPoint(context, pt.x, pt.y);

    for (int i = 0; i < points; i = i + 1) {
        // Calculate next inner point (moving clockwise), accounting for crossing of 0 degrees
        theta = theta - (arcPerPoint / 2.0f);
        if (theta < 0.0f) {
            theta = theta + (2 * M_PI);
        }
        pt = CGPointMake(center.x - (innerRadius * cosf(theta)), center.y - (innerRadius * sinf(theta)));
        CGContextAddLineToPoint(context, pt.x, pt.y);

        // Calculate next outer point (moving clockwise), accounting for crossing of 0 degrees
        theta = theta - (arcPerPoint / 2.0f);
        if (theta < 0.0f) {
            theta = theta + (2 * M_PI);
        }
        pt = CGPointMake(center.x - (outerRadius * cosf(theta)), center.y - (outerRadius * sinf(theta)));
        CGContextAddLineToPoint(context, pt.x, pt.y);
    }
    CGContextClosePath(context);
    CGContextSetLineWidth(context, strokeWidth);
    [fill setFill];
    [stroke setStroke];
    CGContextDrawPath(context, kCGPathFillStroke);
}

Works for me for most basic stars. Tested from 2 points (makes a good diamond!) up to 9 stars.

If you want a star with point down, change the subtraction to addition.

To draw multiples, create a loop and call this method multiple times, passing a new center each time. That should line them up nicely!