Ios – CGContextSetFillColorWithColor: invalid context 0x0

core-graphicsiosobjective c

CGContextSetFillColorWithColor: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.

I'm getting the error from the [color setFill] line of this method. Any ideas on how I can resolve it?

+ (UIImage *)fillImage:(UIImage*)image withColor:(UIColor *)color
{

    // begin a new image context, to draw our colored image onto
    UIGraphicsBeginImageContextWithOptions(image.size, NO, [[UIScreen mainScreen] scale]);

    // get a reference to that context we created
    CGContextRef context = UIGraphicsGetCurrentContext();

    // set the fill color
    [color setFill];

    // translate/flip the graphics context (for transforming from CG* coords to UI* coords
    CGContextTranslateCTM(context, 0, image.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // set the blend mode to overlay, and the original image
    CGContextSetBlendMode(context, kCGBlendModeOverlay);
    CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);
    //if(overlay) CGContextDrawImage(context, rect, img.CGImage);

    // set a mask that matches the shape of the image, then draw (overlay) a colored rectangle
    CGContextClipToMask(context, rect, image.CGImage);
    CGContextAddRect(context, rect);
    CGContextDrawPath(context,kCGPathFill);

    // generate a new UIImage from the graphics context we drew onto
    UIImage *coloredImg = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    //return the color-burned image
    return coloredImg;
}

Best Answer

Your image.size isn't valid, so UIGraphicsBeginImageContextWithOptions isn't creating a graphics context. Both image.size.width and image.size.height must be positive, finite numbers.

Possibly image itself is nil. When you send the size message to nil, you get back CGSizeZero.

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Well after a TON of experimentation I think I have found the fastest way to handle situations like this. The drawing operation above which was taking 6+ seconds now .1 seconds. YES. Here's what I discovered:

Homogenize your contexts & images with a pixel format! The root of the question I asked boiled down to the fact that the CGImages inside a UIImage were using THE SAME PIXEL FORMAT as my context. Therefore fast. The CGImages were a different format and therefore slow. Inspect your images with CGImageGetAlphaInfo to see which pixel format they use. I'm using kCGImageAlphaNoneSkipLast EVERYWHERE now as I don't need to work with alpha. If you don't use the same pixel format everywhere, when drawing an image into a context Quartz will be forced to perform expensive pixel-conversions for EACH pixel. = SLOW
USE CGLayers! These make offscreen-drawing performance much better. How this works is basically as follows. 1) create a CGLayer from the context using CGLayerCreateWithContext. 2) do any drawing/setting of drawing properties on THIS LAYER's CONTEXT which is gotten with CGLayerGetContext. READ any pixels or information from the ORIGINAL context. 3) When done, "stamp" this CGLayer back onto the original context using CGContextDrawLayerAtPoint.This is FAST as long as you keep in mind:
1) Release any CGImages created from a context (i.e. those created with CGBitmapContextCreateImage) BEFORE "stamping" your layer back into the CGContextRef using CGContextDrawLayerAtPoint. This creates a 3-4x speed increase when drawing that layer. 2) Keep your pixel format the same everywhere!! 3) Clean up CG objects AS SOON as you can. Things hanging around in memory seem to create strange situations of slowdown, probably because there are callbacks or checks associated with these strong references. Just a guess, but I can say that CLEANING UP MEMORY ASAP helps performance immensely.

Ios – Modern technique of adding gradient to UIView

As Fogmeister suggested above, do it in the drawRect: method of your UIView subclass.

- (void)drawRect:(CGRect)rect
{
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = UIGraphicsGetCurrentContext();

    NSArray *gradientColors = [NSArray arrayWithObjects:(id) [UIColor redColor].CGColor, [UIColor yellowColor].CGColor, nil];

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    CGGradientRelease(gradient);
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}

Best Answer

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