c++iosc-preprocessorcore-video

Can't do typedef neither for CVOpenGLESTextureGetName nor for CVOpenGLTextureGetName

I have some cross-platform code in .cpp file which converts CVPixelBuffer to CVOpenGLESTextureRef/CVOpenGLTextureRef. To make CoreVideo-related functions cross-platform, I do the following in header file:

#ifdef IOS_SHARED_SUPPORT
#import <OpenGLES/EAGL.h>
#import <CoreVideo/CoreVideo.h>
#import <CoreVideo/CVOpenGLESTexture.h>
#import <CoreVideo/CVOpenGLESTextureCache.h>
#endif // IOS_SHARED_SUPPORT

#ifdef MAC_SHARED_SUPPORT
#import <CoreVideo/CoreVideo.h>
#import <CoreVideo/CVOpenGLTexture.h>
#import <CoreVideo/CVOpenGLTextureCache.h>
#import <AppKit/AppKit.h>
#endif // MAC_SHARED_SUPPORT

#ifdef IOS_SHARED_SUPPORT
typedef CVOpenGLESTextureRef CVOpenGLPlatformTexture;
typedef CVOpenGLESTextureCacheRef CVOpenGLPlatformTextureCache;
typedef CVOpenGLESTextureGetName CVOpenGLPlatformTextureGetName; // error!!!
#endif
#ifdef MAC_SHARED_SUPPORT
typedef CVOpenGLTextureRef CVOpenGLPlatformTexture;
typedef CVOpenGLTextureCacheRef CVOpenGLPlatformTextureCache;
typedef CVOpenGLTextureGetName CVOpenGLPlatformTextureGetName; // error!!!
#endif

It says "Unknown type name 'CVOpenGLESTextureGetName'; did you mean 'CVOpenGLESTextureRef'?", despite of the fact that <CoreVideo/CVOpenGLESTexture.h> is included, and CVOpenGLESTextureRef can be used in typedef.

Can't functions be typedef'ed?
Can you suggest some experiments?
Thanks in advance.

Solution

  • Can't functions be typedef'ed?

    Functions? No. Function types however may be aliased. You can obtain the function type with the decltype operator:

    typedef decltype(CVOpenGLESTextureGetName) CVOpenGLPlatformTextureGetName;

    And CVOpenGLPlatformTextureGetName will become an alias for GLuint(CVOpenGLESTexture), the function type of CVOpenGLESTextureGetName.

    That above of course doesn't do what you want, since I suspect you just want to give another name to the function. You can do that with a constexpr pointer to it:

    constexpr auto* CVOpenGLPlatformTextureGetName = &CVOpenGLESTextureGetName;

    And that's it. CVOpenGLPlatformTextureGetName will be evaluated at compile time as "another name" for the function you initialize it with.