Question

I have the following dispatch_async code:

dispatch_async(openGLESContextQueue, ^{

        [(EAGLView *)self.view setFramebuffer];

        // Replace the implementation of this method to do your own custom drawing.
        static const GLfloat squareVertices[] = {
            -0.5f, -0.33f,
            0.5f, -0.33f,
            -0.5f,  0.33f,
            0.5f,  0.33f,
        };

        static const GLubyte squareColors[] = {
            127, 127,   0, 127,
            0,   255, 255, 255,
            0,     0,   0,   0,
            255,   0, 255, 255,
        };

        static float transY = 0.0f;

        glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);            

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        glTranslatef(0.0f, (GLfloat)(sinf(transY)/2.0f), 0.0f);
        transY += 0.075f;

        glVertexPointer(2, GL_FLOAT, 0, squareVertices);
        glEnableClientState(GL_VERTEX_ARRAY);
        glColorPointer(4, GL_UNSIGNED_BYTE, 0, squareColors);
        glEnableClientState(GL_COLOR_ARRAY);

        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

        [(EAGLView *)self.view presentFramebuffer];

    });

And when in Instruments, and even though the animation is running fine, I get tons of “64 bytes malloc”s that never get freed. Anyone know why?

Answer 1

I was finally able to solve the problem using semaphores:

if (dispatch_semaphore_wait(frameRenderingSemaphore, DISPATCH_TIME_NOW) == 0)
    {
        dispatch_async(openGLESContextQueue, ^{

            [(EAGLView *)self.view setFramebuffer];

            glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
            glClear(GL_COLOR_BUFFER_BIT);

            glMatrixMode(GL_PROJECTION);
            glLoadIdentity();
            glMatrixMode(GL_MODELVIEW);
            glLoadIdentity();
            glTranslatef(0.0f, (GLfloat)(sinf(transY)/2.0f), 0.0f);
            transY += 0.075f;

            glVertexPointer(2, GL_FLOAT, 0, squareVertices);
            glEnableClientState(GL_VERTEX_ARRAY);
            glColorPointer(4, GL_UNSIGNED_BYTE, 0, squareColors);
            glEnableClientState(GL_COLOR_ARRAY);

            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

            [(EAGLView *)self.view presentFramebuffer];

            dispatch_semaphore_signal(frameRenderingSemaphore);
        });
    }

I guess the dispatch queue was getting flooded without time to handle every opengl redraw. This way, it will only process one redraw at a time, asynchronously. Curiously, it has no side effects on the frame rate! 😀

Thanks 🙂