Question

I just got started on a renderer for my cross platform framework (iOS and Android) using opengl es. When I got to the viewport stuff (which is needed for splitscreen stuff) and noticed there is a difference between iOS and Android. Here are two images.

Android
There is actually another glitch. IT seems to wrap.

iOS

My question.
Which of the two is correct? I have no transformations applied but one to bring the drawn quad back a bit. glTranslatef(0.0f, 0.0f, -5.f);

Initialisation code:

glEnable(GL_TEXTURE_2D);
glShadeModel(GL_SMOOTH);            //Enable Smooth Shading
glClearColor(0.f, 0.f, 0.f, 1.0f);  //Black Background
glClearDepthf(1.0f);                    //Depth Buffer Setup
glEnable(GL_DEPTH_TEST);            //Enables Depth Testing
glDepthFunc(GL_LEQUAL);             //The Type Of Depth Testing To Do

//Really Nice Perspective Calculations
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

Viewport and project code

glViewport(viewportX, viewportY, viewportW, viewportH);.

glEnable(GL_SCISSOR_TEST);
glScissor(viewportX, viewportY, viewportW, viewportH);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();

… And finally the frustrum is calculated and set glFrustrum.
I have also used this code:

float widthH = width * .1f;
float heightH = height * .1f;
glOrthof(-widthH, widthH, -heightH, heightH, .1f, 100.f);
glScalef(widthH, heightH, 1.f);

Maybe Android or iOS has something set by default? I am clueless.

Answer 1

Answering my own question for those who have the same issue.

I use GLKView which apparently calls the glViewport on each render call, resetting what I just did in the previous frame. So if you use GLKView make sure to call glViewport each frame! … or roll your own EAGLView to have some real control which I think, I am about to.