iOS, Generated images, and masking - ios

Question

I'm trying to generate an image that is lozenge-shaped and shows some percentage finished versus unfinished. The way I implemented this was as follows:
Generate 2 rectangles - one the size of the filled region, the other the size of the empty rectange
Invoke UIGrapicsBeginImageContext() with the size of the rectangle I am interested in
Draw the 2 rectangles in the context side-by side
Grab the image from the context and end the context
Create a new masked image by using CGImageMaskCreate() followed by CGImageCreateWithMask() and extracting the masked image
I generate the filled and empty bitmaps using category extensions to UIImage, and then apply a static mask image to them.
The Problem: This works fine in the simulator, but the masking doesn't work on a real device.
Instead of including the code here, I'm including a link to a project that has the code. The relevant files are:
UIImage.h/UIImage.m: The category extension to UIImage that adds both the "create an image with a specified color" and "create a masked image using the supplied mask".
TLRangeDisplay.h/TLRangeDisplay.m: the code for my lozenge-shaped status display. The routine of interest there is fillWithRect().
Here is the code I added to UIImage (via a category):
+ (UIImage *)imageWithColor:(UIColor *)color {
CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, rect);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
+ (UIImage *)imageWithColor:(UIColor *)color andSize:(CGSize)size {
CGRect rect = CGRectMake(0.0f, 0.0f, size.height, size.width);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, rect);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
- (UIImage*) maskWith:(UIImage *)maskImage {
CGImageRef maskRef = maskImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef), CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef), CGImageGetBytesPerRow(maskRef), CGImageGetDataProvider(maskRef), NULL, false);
CGImageRef masked = CGImageCreateWithMask([self CGImage], mask);
UIImage* image = [UIImage imageWithCGImage:masked];
CFRelease(mask);
CFRelease(masked);
return image;
}
And here is the routine that does the masking:
-(void)fillWithRect {
CGRect f = self.frame;
CGFloat width = f.size.width;
CGFloat fullRange = maxValue_ - minValue_;
CGFloat filledRange = currentValue_ - minValue_;
CGRect fillRect = CGRectMake(0, 0, (filledRange * width) / fullRange, f.size.height);
CGRect emptyRect = CGRectMake(fillRect.size.width, 0, width - fillRect.size.width, f.size.height);
UIImage *fillImage = nil;
UIImage *emptyImage = nil;
if(fillRect.size.width > 0) {
fillImage = [UIImage imageWithColor:fillColor_ andSize:fillRect.size];
}
if(emptyRect.size.width > 0) {
emptyImage = [UIImage imageWithColor:emptyColor_ andSize:emptyRect.size];
}
// Build the 2-color image
UIGraphicsBeginImageContext(f.size);
[fillImage drawInRect:fillRect];
[emptyImage drawInRect:emptyRect];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
// Mask it
if(nil != maskImage_)
image = [image maskWith:maskImage_];
CGRect fullRect = CGRectMake(0, 0, f.size.width, f.size.height);
// Merge ith with the shape
UIGraphicsBeginImageContext(f.size);
[image drawInRect:fullRect];
[shapeImage_ drawInRect:fullRect];
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[shownView_ removeFromSuperview];
shownView_ = [[UIImageView alloc] initWithImage:image];
[self addSubview:shownView_];
if(nil != shownView_)
[self bringSubviewToFront:shownView_];
}
The project can be downloaded from http://dl.dropbox.com/u/5375467/ColorPlayOS4.zip
Thanks for any insights on this problem!