View Full Version : Very Basic OpenGL ES problem

May 6, 2009, 05:31 AM
I am trying to do some basic OpenGL ES with my iPhone, but I have some problems doing so. In my Xcode, I have created a new OpenGL ES based application project and I have changed the drawView function in the EAGLView.m file to look like this:

- (void)drawView {


[EAGLContext setCurrentContext:context];
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glViewport(0, 0, backingWidth, backingHeight);


glOrthof(-100.0f, 100.0f, -150.0f, 150.0f, -100.0f, 100.0f);

static GLfloat rotation = 0.0f;

glRotatef(rotation, 0.0f, 1.0f, 0.0f);
rotation += 1.0f;

glClearColor(1.0f, 1.0f, 1.0f, 1.0f);

const GLfloat squareVertices[] = {
-50.0f, -50.0f, -1.0f,
50.0f, -50.0f, -1.0f,
-50.0f, 50.0f, -1.0f,
50.0f, 50.0f, -1.0f,

glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
glVertexPointer(3, GL_FLOAT, 0, squareVertices);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

const GLubyte squareColors[] = {
255, 255, 0, 255,
255, 255, 0, 255,
0, 0, 0, 0,
255, 0, 255, 255,

glColorPointer(4, GL_UNSIGNED_BYTE, 0, squareColors);

const GLfloat squareVertices2[] = {
-40.0f, -40.0f, -12.0f,
40.0f, -40.0f, -12.0f,
-40.0f, 40.0f, -12.0f,
40.0f, 40.0f, -12.0f,

glVertexPointer(3, GL_FLOAT, 0, squareVertices2);
glDrawArrays(GL_TRIANGLE_STRIP,0, 4);

glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];

Although I can get my two rotating squares, when the rotation is 180 degrees, the smaller square still seems to be in front of the bigger one, but this should not happen... I know the answer is simple but I can't find it! I have already enabled GL_DEPTH_TEST as you can see. The same thing happens if I try setting the z value of the smaller square to something else (like a positive value).

Can anyone help?

May 6, 2009, 11:56 AM
Did you create your framebuffer with a z buffer?

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