CARenderer Memory Issue

FROM : Colin Cornaby
DATE : Mon Mar 24 02:51:06 2008

I sent an email to the list earlier asking about CoreAnimation memory 
use. I think I have that all resolved now, except for one memory usage 
issue with CARenderer.

I am successfully rendering a layer tree that is never shown on the 
screen with a CARenderer. I set up a pixel buffer, and then render to 
the pixel buffer. But, when I call [CATransaction commit] before I 
actually do the rendering, there is a very large allocation of memory 
depending on the size of the image. Apparently glClear is being called 
internally by CoreAnimation, and I'm guessing it's allocating some 
sort of buffer internal to CoreAnimation. I can't figure out how to 
get CoreAnimation to let go of it, and it exists for the lifetime of 
my program.

Here is the complete event log of the memory at the address in 
question (note the lack of a free event):
#    Category    Event Type    Timestamp    Address    Size    Responsible Library    
Responsible Caller
0    GeneralBlock-36003840    Malloc    00:14.930    0x254cf000    36003840    
libGL.dylib    glClear

The stack trace from where the memory is allocated:
    0 libSystem.B.dylib malloc
    1  0x179b1e3c
    2  0x179a37d8
    3  0x179a6af1
    4 libGL.dylib glClear
    5 MyProgram -[GSOGLLayerRenderer imageByRenderingLayers:] /
Users/....
    6 MyProgram -[GSImageExporterController prepareImage] /Users/....
    7 MyProgram -[MyDocument export:] /Users/....
    8 AppKit -[NSApplication sendAction:to:from:]
    9 AppKit -[NSMenu performActionForItemAtIndex:]
  10 AppKit -[NSCarbonMenuImpl 
performActionWithHighlightingForItemAtIndex:]
  11 AppKit AppKitMenuEventHandler
  12 HIToolbox DispatchEventToHandlers(EventTargetRec*, 
OpaqueEventRef*, HandlerCallRec*)
  13 HIToolbox SendEventToEventTargetInternal(OpaqueEventRef*, 
OpaqueEventTargetRef*, HandlerCallRec*)
  14 HIToolbox SendEventToEventTarget
  15 HIToolbox SendHICommandEvent(unsigned long, HICommand const*, 
unsigned long, unsigned long, unsigned char, OpaqueEventTargetRef*, 
OpaqueEventTargetRef*, OpaqueEventRef**)
  16 HIToolbox SendMenuCommandWithContextAndModifiers
  17 HIToolbox SendMenuItemSelectedEvent
  18 HIToolbox FinishMenuSelection(MenuData*, MenuData*, MenuResult*, 
MenuResult*, unsigned long, unsigned long, unsigned long, unsigned char)
  19 HIToolbox MenuSelectCore(MenuData*, Point, double, unsigned 
long, OpaqueMenuRef**, unsigned short*)
  20 HIToolbox _HandleMenuSelection2
  21 HIToolbox _HandleMenuSelection
  22 AppKit _NSHandleCarbonMenuEvent
  23 AppKit _DPSNextEvent
  24 AppKit -[NSApplication 
nextEventMatchingMask:untilDate:inMode:dequeue:]
  25 AppKit -[NSApplication run]
  26 AppKit NSApplicationMain
  27 MyProgram main /Users/....
  28 MyProgram start

Here are the relevant snippets of my code (with the line the large 
memory allocation occurs on noted):
NSOpenGLPixelFormatAttribute attr[] =
{
   NSOpenGLPFAOffScreen,
   NSOpenGLPFADepthSize, 24,
   (CGLPixelFormatAttribute) 0
};
NSOpenGLPixelFormat *format = [[NSOpenGLPixelFormat alloc] 
initWithAttributes:attr];
m_glContext = [[NSOpenGLContext alloc] initWithFormat:format 
shareContext:nil];
m_renderer = [CARenderer rendererWithCGLContext:[m_glContext 
CGLContextObj] options:NULL];
[m_renderer retain];
[m_glContext retain];
m_renderFrame = frame;
int imageWidth = ceil(m_renderFrame.size.width);
int imageHeight = ceil(m_renderFrame.size.height);
int imageSize = imageWidth*imageHeight*4;
glData = malloc(GL_ALIGN(imageSize));
[m_glContext setOffScreen:glData width:imageWidth height:imageHeight 
rowbytes:imageWidth*4];
NSOpenGLContext *oldContext = [NSOpenGLContext currentContext];
[oldContext retain];
[m_glContext makeCurrentContext];
glClearColor(0, 0.0, 0.0, 0.0);
glViewport (0.0, 0.0, imageWidth, imageHeight);
glLoadIdentity ();
glOrtho (frame.origin.x, frame.origin.x+imageWidth, frame.origin.y, 
frame.origin.y+imageHeight, -1, 1);
....some more setup code here....
[m_glContext makeCurrentContext];
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
[CATransaction commit]; <-large memory allocation occurs here
[m_renderer beginFrameAtTime:0.0 timeStamp:NULL];
[m_renderer addUpdateRect:CGRectMake(m_renderFrame.origin.x, 
m_renderFrame.origin.y, imageWidth,imageHeight)];
[m_renderer render];
[m_renderer endFrame];
glPixelStorei(GL_PACK_ALIGNMENT, 1);
...read the pixels here...

If anyone had any suggestions, or could let me know what's going on 
here, I'd appreciate it. I'm really bad with pixel buffers, and I'm 
not sure why. Something about drawing something I can't see disagrees 
with me I guess. :)

Thanks,
Colin