@implementation someCAOpenGLLayerSubclass

// ...

-(void)drawInCGLContext:(CGLContextObj)ctx pixelFormat:(CGLPixelFormatObj)pf forLayerTime:(CFTimeInterval)t displayTime:(const CVTimeStamp *)ts
{
    // the pf parameter is changed after the first few calls   
    if(_initialPF)
    {
        _initialPF = (long)(void*)pf;
    }
    else if(initialFormat != (long)(void*)pf)
    {
       // do horde stuff if the pixel format has been re-created   
    }
   
    [super drawInCGLContext:ctx pixelFormat:pf forLayerTime:t displayTime:ts];
}