Drawing Pie Charts using iPhone SDK

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#import "GraphView.h"
 
#define PI 3.14159265358979323846
static inline float radians(double degrees) { return degrees * PI / 180; }
 
@implementation GraphView
 
- (void)drawRect:(CGRect)rect {
 
        CGRect parentViewBounds = self.bounds;
        CGFloat x = CGRectGetWidth(parentViewBounds)/2;
        CGFloat y = CGRectGetHeight(parentViewBounds)*0.55;
 
    // Get the graphics context and clear it
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextClearRect(ctx, rect);
 
        // define stroke color
        CGContextSetRGBStrokeColor(ctx, 1, 1, 1, 1.0);
 
        // define line width
        CGContextSetLineWidth(ctx, 4.0);
 
 
       // need some values to draw pie charts
 
        double snapshotCapacity =20;
        double rawCapacity = 100;
        double systemCapacity = 1;
 
        int offset = 5;
        double pie1_start = 315.0;     
        double pie1_finish = snapshotCapacity *360.0/rawCapacity; 
        double system_finish = systemCapacity*360.0/rawCapacity;
 
    CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor greenColor] CGColor]));
    CGContextMoveToPoint(ctx, x+2*offset, y);     
    CGContextAddArc(ctx, x+2*offset, y, 100,  radians(snapshot_start), radians(snapshot_start+snapshot_finish), 0); 
    CGContextClosePath(ctx); 
    CGContextFillPath(ctx); 
 
        // system capacity 
        CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor colorWithRed:15 green:165/255 blue:0 alpha:1 ] CGColor]));
        CGContextMoveToPoint(ctx, x+offset,y);     
    CGContextAddArc(ctx, x+offset, y, 100,  radians(snapshot_start+snapshot_finish+offset), radians(snapshot_start+snapshot_finish+system_finish), 0); 
    CGContextClosePath(ctx); 
    CGContextFillPath(ctx); 
 
        /* data capacity */
        CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor colorWithRed:99/255 green:184/255 blue:255/255 alpha:1 ] CGColor]));
        CGContextMoveToPoint(ctx, x, y);     
    CGContextAddArc(ctx, x, y, 100,  radians(snapshot_start+snapshot_finish+system_finish+offset), radians(snapshot_start), 0); 
    CGContextClosePath(ctx); 
    CGContextFillPath(ctx);       
}