How to stop iOS EAGLContext's memory from growing? - ios

Question

In this super simple app that uses a GLKViewController to display a red screen the memory keeps growing.
ViewController.h:
#import <UIKit/UIKit.h>
#import <GLKit/GLKit.h>
#interface ViewController : GLKViewController
#end
ViewController.m:
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController {
EAGLContext* context;
}
- (void)viewDidLoad {
[super viewDidLoad];
context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
GLKView* view = (GLKView*)self.view;
view.context = context;
view.drawableDepthFormat = GLKViewDrawableColorFormatRGBA8888;
[EAGLContext setCurrentContext:context];
self.preferredFramesPerSecond = 60;
}
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
#end
For each frame 9*64 bytes is allocated and never freed as seen in this image (note that the transient count is 0 for IOAccellResource):
This is what the allocation list and stacktrace looks like:
The memory "leak" is small but it still managed to use up 6.5 MB despite only running for less than 3 minutes.
Is there a bug in the EAGLContext or is there something I can do about this? I have noticed (I'm new to iOS development) that other parts of Apple's API uses zone allocators and the memory usage keeps growing when it really should have been in some kind of steady state mode. That makes me think I have missed something (I have tried to send it LowMemory but nothing happen).

Answer 1

So from your comment you say that you are using some other code that is written in C++ and basically all you need is the connection to the actual buffer to be presented. I will assume none of that "C++" code you mentioned is inflating your memory and you have actually try to create a new application only adding the code you posted just to be 100% sure...
To migrate off the GLKit is then very easy for you. Simply subclass the UIView which will be used to drawing and add a few methods:
This needs to be overridden so you can get the render buffer from the view
+ (Class)layerClass {
return [CAEAGLLayer class];
}
The context is already done correctly and needs to be used.
You need to setup the buffers manually. I use a custom class but I believe you will be able to see what is going on here and possibly remove the code you don't need.
- (void)loadBuffersWithView:(UIView *)view
{
self.view = view;
CAEAGLLayer *layer = (CAEAGLLayer *)view.layer;
layer.opaque = YES;
if ([[UIScreen mainScreen] respondsToSelector:#selector(displayLinkWithTarget:selector:)]) {
layer.contentsScale = [UIScreen mainScreen].scale;
}
GLuint frameBuffer; // will hold the generated ID
glGenFramebuffers(1, &frameBuffer); // generate only 1
self.frameBuffer = frameBuffer; // assign to store as the local variable
[self bindFrameBuffer];
GLuint renderBuffer; // will hold the generated ID
glGenRenderbuffers(1, &renderBuffer); // generate only 1
self.renderBuffer = renderBuffer; // assign to store as the local variable
[self bindRenderBuffer];
[self.context.glContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:layer];
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, self.renderBuffer);
GLint width, height;
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &width);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &height);
self.bufferSize = CGSizeMake(width, height);
glViewport(0, 0, width, height);
[GlobalTools framebufferStatusValid];
[GlobalTools checkError];
}
On present you need to call presentRenderbuffer on your context with the appropriate render buffer id.
Rest of your code should be the same. But remember to also tear down the openGL when you do not need it and possibly explicitly delete all the buffers that were generated on the GPU.

Answer 2

I printed out the amount of resident memory to the screen and noticed that the memory didn't increase when the device was disconnected from the debugger.
It turns out that using the "Zombie instrument" was causing this... I swear that I saw the memory increase in the memory view of the debugger too, but now I can't repeat it (haven't changed anything in the scheme).