CODEWITHSUNDEEP
ioscore-graphics
John Gaby
John Gaby

Reputation: 1512

Cannot paint image created using CGBitmapContextCreate

Under IOS I am trying to create an image by drawing into a context created via CGBitmapContextCreate. The following is the code that I am using (which is similar to some examples that I found), but when I call it, nothing is painted. Note that 'context' in this example is obtained via a call to UIGraphicsGetCurrentContext and I can successfully paint other things into this context. Is there something that I am missing?

Thanks

    CGContextRef bmContext;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    bmContext = CGBitmapContextCreate(nil, 200, 200, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);

    CGFloat Color[4] = {    
        (CGFloat) 1,
        (CGFloat) 0,
        (CGFloat) 0,
        (CGFloat) 1 };
    CGRect Rect = { { 0, 0 }, { 200, 200 } };

    CGContextSetFillColor(bmContext, Color);
    CGContextFillRect (bmContext, Rect);

    CGImageRef image = CGBitmapContextCreateImage(bmContext);  

    CGContextDrawImage(context, CGRectMake(100, 100, 200, 200), image);

    CGImageRelease(image);
    CGContextRelease(bmContext);
    CFRelease(colorSpace);

Upvotes: 2

Views: 1260

Answers (1)

John Gaby
John Gaby

Reputation: 1512

After much experimentation I have found the problem. It appears that I need to call:

CGContextSetFillColorSpace(bmContext, colorSpace);

Otherwise it appears to be a grey scale context and is expecting only 2 values when I set the fill color, an intensity and an alpha. This means that in my example above, the alpha was always zero resulting in nothing being drawn. Setting the context to a RGB colorspace fixes the problem.

Thanks to all who took time to look at my problem.

Upvotes: 1

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