gistfile1.m

//
//  GOParametricView.m
//  CircleTest
//
//  Created by Samuel Goodwin on 5/1/12.
//

#import "GOParametricView.h"
#import <QuartzCore/QuartzCore.h>

const CGFloat dotWidth = 10.0f;

@implementation GOParametricView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setBackgroundColor:[UIColor whiteColor]];
        [self setClearsContextBeforeDrawing:NO];
        _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(setNeedsDisplay)];
        [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
        _startDate = [NSDate date];
    }
    return self;
}

- (void)drawRect:(CGRect)rect{
    // yay parametrics!
    // y = sin(omega *t), omega = 2*pi*f
    // x = cos(omega *t), omega = 2*pi*f
    
    CGFloat magnitude = 50.0f;
    CGFloat t = -1.0f*((CGFloat)[self.startDate timeIntervalSinceNow]);
    CGFloat x = magnitude*cosf(2*M_PI*self.xFrequency*t);
    CGFloat y = magnitude*sinf(2*M_PI*self.yFrequency*t);
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextTranslateCTM(context, CGRectGetWidth(rect)/2.0f, CGRectGetHeight(rect)/2.0f);
    
    CGContextSetLineWidth(context, 20.0f);
    
    CGContextFillEllipseInRect(context, [self rectWithCenterPoint:CGPointMake(0.0f, 0.0f)]);
    CGContextFillEllipseInRect(context, [self rectWithCenterPoint:CGPointMake(x, y)]);
}

@end