CGContext strangeness - ios

Question

I have a little code module that should refer as signature panel so that the user can sign on this panel with his finger. The whole thing runs on the iPad.
Now, I managed to do the usual touchesBegan(), touchesMoved(), touchesEnded() carousel to make him sign on that panel. While signing, I draw his signature on the main view. However, due to whatever reason, the image appears twice: once correctly and once upside down above the main signature (see image). Since I don't see any translating being done in my code, I suspect that the whole code might be incorrect, but I don't know why. Does anyone know what I'm doing wrong here?
#import "RMSignatureView.h"
#import <QuartzCore/QuartzCore.h>
#interface RMSignatureView() {
CGPoint origin;
}
-(void) setupLayer;
#property (nonatomic, retain) UIImage* image;
#end
#implementation RMSignatureView
#synthesize image;
-(void) dealloc {
[image release];
[super dealloc];
}
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
[self setupLayer];
}
return self;
}
-(id) initWithCoder:(NSCoder *)aDecoder {
if ([super initWithCoder:aDecoder] == self) {
[self setupLayer];
}
return self;
}
-(void) setupLayer {
self.layer.cornerRadius = 10;
self.layer.borderColor = [UIColor colorWithRed:109.0/256.0 green:149.0/256.0 blue:224.0/256.0 alpha:1.0].CGColor;
self.layer.borderWidth = 0.5f;
}
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGContextSetStrokeColorWithColor(context, [UIColor grayColor].CGColor);
CGFloat sizes[2];
sizes[0] = 1;
sizes[1] = 1;
CGContextSetLineDash(context, 0, sizes, 2);
CGContextMoveToPoint(context, rect.origin.x + 50, rect.origin.y + rect.size.height - 30);
CGContextAddLineToPoint(context, rect.origin.x + rect.size.width - 50, rect.origin.y + rect.size.height - 30);
CGContextStrokePath(context);
CGContextSetLineDash(context, 0, NULL, 0);
if (image)
CGContextDrawImage(context, rect, image.CGImage);
CGContextRestoreGState(context);
}
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touch = [touches anyObject];
origin = [touch locationInView:self];
}
-(void) touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
origin.x = -1;
origin.y = -1;
}
-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
origin.x = -1;
origin.y = -1;
}
-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touch = [touches anyObject];
if (origin.x != -1 && origin.y != -1) {
UIGraphicsBeginImageContext(self.frame.size);
#try {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
if (image)
CGContextDrawImage(context, CGRectMake(0, 0, self.frame.size.width, self.frame.size.height), image.CGImage);
CGContextMoveToPoint(context, origin.x, origin.y);
origin = [touch locationInView:self];
CGContextAddLineToPoint(context, origin.x, origin.y);
CGContextStrokePath(context);
self.image = UIGraphicsGetImageFromCurrentImageContext();
CGContextRestoreGState(context);
}
#finally {
UIGraphicsEndImageContext();
}
}
[self setNeedsDisplay];
}
#end

Answer 1

Found it.. Quartz has (0, 0) in the lower left instead of upper left.