CGBitMapContextCreate Method Causes Compiler Warning Xcode 5 not Xcode 4

ios xcode cgcontext xcode5 cgbitmapcontextcreate
jac300 picture jac300 · Sep 16, 2013 · Viewed 8.2k times · Source

I just updated Xcode from version 4.6.2 to 5.0, and after doing a method in my project (created in Xcode 4.6.2) is suddenly giving a compiler warning. I have tried re-opening the project in both the old and new versions of Xcode, and I have confirmed that the same method gives no warnings in 4.6.2.

Here is the line of code eliciting the warning in Xcode 5.0:

CGContextRef context = CGBitmapContextCreate(NULL, frame.size.width * scaleFactor, frame.size.height * scaleFactor, 8, frame.size.width * scaleFactor * 4, colorSpace, kCGImageAlphaPremultipliedFirst);

And the warning says:

"Implicit conversion from enumeration type 'enum CGImageAlphaInfo' to different enumeration type 'CGBitMapInfo' (aka 'enum CGBitMapInfo')"

It does not appear to be a deprecation warning, but I am not quite familiar enough with these classes to interpret the meaning or know how to resolve it. Any help is appreciated.

Answer

nevyn picture nevyn · Nov 12, 2013

The kCGImageAlpha* enum values are supposed to fill the first five bits in CGBitmapInfo. However, since the C type system can't express this, you get a warning that the types don't match, even though they were intended to.

The correct solution is to cast your alpha enum value to CGBitmapInfo, since that's what it is:

(CGBitmapInfo)kCGImageAlphaPremultipliedFirst

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