destroyFramebuffer method in an openGL app - iphone

Question

in my OpenGL type of iphone app, I have this method below in the GLView implementation.
i noticed everytime i started up the app during development that the last frame that was present when i shut the app down the last time, would draw first before the app started its animation...
but when i commented out this method, the app would start up just fine without the old end frame from the last time.
so i have something wrong in here. possibly directly in this method... any ideas?
(now i'm getting a blank white screen (as a first frame) just before the animation, so something is amiss here)
//------------------------------------------------------------------------------------
- (void)destroyFramebuffer
{
NSLog(#"destroyFramebuffer");
glDeleteFramebuffersOES(1, &viewFramebuffer);
viewFramebuffer = 0;
glDeleteRenderbuffersOES(1, &viewRenderbuffer);
viewRenderbuffer = 0;
if(depthRenderbuffer)
{
glDeleteRenderbuffersOES(1, &depthRenderbuffer);
depthRenderbuffer = 0;
}
}
here below is how the "createFrameBuffer" method looks
(the way the GLView implementation was starting up was with these 3 lines):
[EAGLContext setCurrentContext:context];
// [self destroyFramebuffer];
[self createFramebuffer];
//------------------------------------------------------------------------------------
- (BOOL)createFramebuffer
{
NSLog(#"createFramebuffer");
glGenFramebuffersOES(1, &viewFramebuffer);
glGenRenderbuffersOES(1, &viewRenderbuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(CAEAGLLayer*)self.layer];
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, viewRenderbuffer);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
if (USE_DEPTH_BUFFER)
{
glGenRenderbuffersOES(1, &depthRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, backingWidth, backingHeight);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);
}
if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES)
{
NSLog(#"failed to make complete framebuffer object %x", glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES));
return NO;
}
return YES;
}

Answer 1

When you destroy your renderbuffer the memory is reclaimed. The chances of the same memory being used again next time are quite high, but not always guaranteed. You simply need to clear the buffer on creation: (or at least render something that fills the buffer)
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT);
Also it's worth changing your destroy method to check that your framebuffer and renderbuffer even exist, otherwise you may be requesting GL to delete things that you haven't made. For eg:
if (viewFramebuffer) {
glDeleteFramebuffers(1, &viewFramebuffer), viewFramebuffer = 0;
}
if (viewRenderbuffer) {
glDeleteRenderbuffers(1, &viewRenderbuffer), viewRenderbuffer = 0;
}