gistfile1.m

void MethodSwizzle(Class c, SEL orig, SEL new)
{
    Method origMethod = class_getInstanceMethod(c, orig);
    Method newMethod = class_getInstanceMethod(c, new);
    if (class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod))) {
        class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    } else {
        method_exchangeImplementations(origMethod, newMethod);
    }
}





MethodSwizzle(openglcontext, @selector(flushBuffer), @selector(my_flushBuffer));


- (void)my_flushBuffer;
{
    [self my_flushBuffer]; // calls the *original* flushBuffer method (yes it looks weird)
    
    <do whatever you want>
}