how to set up CAEAGLLayer subclass with openGL context: Current draw framebuffer is invalid

Question

I'm trying to set up a CAEAGLLayer subclass with a gl context. That is, instead of creating a UIView subclass which returns a CAEAGLLayer and binding a gl context to this layer from within the UIView subclass, I'm directly subclassing the layer and trying to setup the context in the layer's init, like so:

- (id)init
{
    self = [super init];
    if (self) {
        self.opaque = YES;

        _glContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
        NSAssert([EAGLContext setCurrentContext:_glContext], @"");

        glGenRenderbuffers(1, &_colorRenderBuffer);
        glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderBuffer);
        [_glContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:self];

        glGenFramebuffers(1, &_framebuffer);
        glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _colorRenderBuffer);

        /// . . .

up to that point everything seems fine. However, I then try to create a shader program with a "pass-thru" vertex/fragment shader pair and while linking the program returns no errors, validation fails saying: "Current draw framebuffer is invalid."

The code that links and validates the shader program (after attaching the shaders) looks like so, just in case:

- (BOOL)linkAndValidateProgram
{
    GLint status;
    glLinkProgram(_shaderProgram);

#ifdef DEBUG
    GLint infoLogLength;
    GLchar *infoLog = NULL;
    glGetProgramiv(_shaderProgram, GL_INFO_LOG_LENGTH, &infoLogLength);
    if (infoLogLength > 0) {
        infoLog = (GLchar *)malloc(infoLogLength);
        glGetProgramInfoLog(_shaderProgram, infoLogLength, &infoLogLength, infoLog);
        NSLog(@"Program link log:\n%s", infoLog);
        free(infoLog);
    }
#endif

    glGetProgramiv(_shaderProgram, GL_LINK_STATUS, &status);
    if (!status) {
        return NO;
    }

    glValidateProgram(_shaderProgram);

#ifdef DEBUG
    glGetProgramiv(_shaderProgram, GL_INFO_LOG_LENGTH, &infoLogLength);
    if (infoLogLength > 0) {
        infoLog = (GLchar *)malloc(infoLogLength);
        glGetProgramInfoLog(_shaderProgram, infoLogLength, &infoLogLength, infoLog);
        NSLog(@"Program validation log:\n%s", infoLog);
        free(infoLog);
    }
#endif

    glGetProgramiv(_shaderProgram, GL_VALIDATE_STATUS, &status);
    if (!status) {
        return NO;
    }

    glUseProgram(_shaderProgram);
    return YES;
}

I'm wondering if there might be some extra setup at some point throughout the lifecycle of CAEAGLLayer that I might be unaware of and might be skipping by trying to setup GL in init?

Answer 1

The problem was the layer has no dimensions at that point in init. Which in turn makes it where trying to set the render buffer storage to the layer implies a buffer of 0.

UPDATE: My current best thinking is that, instead of imposing a size on init (which worked fine for the purposes of testing but is kind hacky), I should just re set the buffer storage whenever the layer changes sizes. So I'm overriding -setBounds: like so:

- (void)setBounds:(CGRect)bounds
{
    [super setBounds:bounds];
    [_context renderbufferStorage:GL_RENDERBUFFER fromDrawable:self];
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &someVariableToHoldWidthIfYouNeedIt);
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &someVariableToHoldHeightIfYouNeedIt);
}

Answer 2

As far as I know you have to overwrite the layerClass method in the View, like this

    + (Class)layerClass
    {
       return [MYCEAGLLayer class];
    }

Also you have to set the drawableProperties on the MYCEAGLLayer.