iPhone 画圆角矩形

@implementation BrightnessController

// MyCreateBitmapContext: Source based on Apple Sample Code
CGContextRef MyCreateBitmapContext (int pixelsWide,
int pixelsHigh)
{
    CGContextRef    context = NULL;
    CGColorSpaceRef colorSpace;
    void *          bitmapData;
    int             bitmapByteCount;
    int             bitmapBytesPerRow;

    bitmapBytesPerRow   = (pixelsWide * 4);
    bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

    colorSpace = CGColorSpaceCreateDeviceRGB();
    bitmapData = malloc( bitmapByteCount );
    if (bitmapData == NULL)
    {
        fprintf (stderr, "Memory not allocated!");
CGColorSpaceRelease( colorSpace );
        return NULL;
    }
    context = CGBitmapContextCreate (bitmapData,
pixelsWide,
pixelsHigh,
8,
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast);
    if (context== NULL)
    {
        free (bitmapData);
        fprintf (stderr, "Context not created!");
        return NULL;
    }
    CGColorSpaceRelease( colorSpace );

    return context;
}

// addRoundedRectToPath: Source based on Apple Sample Code
static void addRoundedRectToPath(CGContextRef context, CGRect rect, float ovalWidth,
float ovalHeight)
{
float fw, fh;
if (ovalWidth == 0 || ovalHeight == 0) {
CGContextAddRect(context, rect);
return;
}

CGContextSaveGState(context);
CGContextTranslateCTM(context, CGRectGetMinX(rect), CGRectGetMinY(rect));
CGContextScaleCTM(context, ovalWidth, ovalHeight);
fw = CGRectGetWidth(rect) / ovalWidth;
fh = CGRectGetHeight(rect) / ovalHeight;

CGContextMoveToPoint(context, fw, fh/2);  // Start at lower right corner
CGContextAddArcToPoint(context, fw, fh, fw/2, fh, 1);  // Top right corner
CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 1); // Top left corner
CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 1); // Lower left corner
CGContextAddArcToPoint(context, fw, 0, fw, fh/2, 1); // Back to lower right

CGContextClosePath(context);
CGContextRestoreGState(context);
}

// Build an image tinted at the given percentage
id createImage(float percentage)
{
CGContextRef context  = MyCreateBitmapContext(30, 30);
addRoundedRectToPath(context, CGRectMake(0.0f, 0.0f, 30.0f, 30.0f), 4.0f, 4.0f);
CGFloat gray[4] = {percentage, percentage, percentage, 1.0f};
CGContextSetFillColor(context, gray);
CGContextFillPath(context);
CGImageRef myRef = CGBitmapContextCreateImage (context);
free(CGBitmapContextGetData(context));
CGContextRelease(context);
return [UIImage imageWithCGImage:myRef];
}

#define MAXDEPTH 8

-(BrightnessController *) initWithBrightness: (int) aBrightness
{
self = [super init];
brightness = aBrightness;
self.title = [NSString stringWithFormat:@"%d%%", brightness * 10];
[self.tabBarItem initWithTitle:self.title image:createImage(((float) brightness / 10.0f)) tag:0];
return self;
}

- (void)loadView
{
UIView *contentView = [[UIView alloc] i