Using depth buffer on iOS with OpenGL ES 1.1.

Question

Hello, I'm trying to get a depth buffer working so I can start making a game for iOS. I'm fine with OpenGL and Objective-C for OSX but this is my first time making an iphone application.

I removed the ES1Renderer and ES2Renderer classes and moved the ES1 code into the EAGLView class. The default animation worked when I did that. When I tried to use perspective it went wrong. I get a white screen now. Can someone tell me what I'm doing wrong?

In the initialisation method:

// Create default framebuffer object.
    glGenFramebuffersOES(1, &defaultFramebuffer);
    glGenRenderbuffersOES(1, &colorRenderbuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, defaultFramebuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorRenderbuffer);
    //Initialisation code for the game's graphics and to develop the scene
    glEnable(GL_DEPTH_TEST); //Enables Depth Testing
    glDepthFunc(GL_LEQUAL);
    glDepthMask(GL_TRUE);
    //glEnable(GL_CULL_FACE);
    //glCullFace(GL_FRONT);
    //Setup projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    double xmax = 0.04142135624 * ((float) backingWidth)/backingHeight;
    glFrustumf(-xmax, xmax, -0.04142135624, 0.04142135624, 0.1, 2000); //The ymax and min have been precalculated
    glMatrixMode(GL_MODELVIEW); //Select The Modelview Matrix
    glLoadIdentity();

In the drawView method:

    static const GLfloat squareVertices[] = {
        1,   1,-0.1f,
        -1,   1,-0.1f,
        1,  -1,0.1f,
        -1,  -1,0.1f,
    };

    static const GLubyte squareColors[] = {
        0,0,200,255,
        40,90,250,255,
        0,0,200,255,
        50,100,230,255,
    };
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glClear(GL_DEPTH_BUFFER_BIT);
    glVertexPointer(3, 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);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];

In the layoutSubviews method:

// Allocate color buffer backing based on the current layer size
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    [context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(CAEAGLLayer*) self.layer];
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
    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;
    [self drawView:nil];

I've done everything it seems I have to do. I don't know why it's so much more complicated for iOS.

Thankyou for any help.

Answer 1

I might be reading this wrong, but you are defining a clipping box with:

glFrustumf(-xmax, xmax, -0.04142135624, 0.04142135624, 0.1, 2000);

And the object that you're trying to render with:

static const GLfloat squareVertices[] = { 
        1,   1,-0.1f, 
        -1,   1,-0.1f, 
        1,  -1,0.1f, 
        -1,  -1,0.1f, 
    };

At the top you are clipping Z values from 0.1 to 2000. But your vertices have Z values from -0.1 to 0.1. These don't see to overlap.

You might want to try moving the object that you want to look at into the area where you can see it.

Answer 2

Have a look at the code you can find at this page the author inits an EAGLView subclass parametrizing the method in the case he needs a depth buffer