CODEWITHSUNDEEP
iosopengl-esviewport
PPR
PPR

Reputation: 39

Multiple Viewport OpenGL ES

I am currently trying to make an ios app that uses multiple opengl es viewports (i.e. a split screen). Here's how I'm doing it:

// Create default framebuffer object. The backing will be allocated for the current layer in -resizeFromLayer
    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);

// Replace the implementation of this method to do your own custom drawing
const GLfloat squareVertices[] = {
  -0.5f, -0.5f,
  0.5f,  -0.5f,
  -0.5f,  0.5f,
  0.5f,   0.5f,
};
const GLubyte squareColors[] = {
  255, 255,   0, 255,
  0,   255, 255, 255,
  0,     0,   0,   0,
  255,   0, 255, 255,
 };

[EAGLContext setCurrentContext:context];

glBindFramebufferOES(GL_FRAMEBUFFER_OES, defaultFramebuffer);
glViewport(0, backingHeight/2, backingWidth/2, backingHeight/2);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(-1.0f, 1.0f, -1.5f, 1.5f, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);
glRotatef(3.0f, 0.0f, 0.0f, 1.0f);

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

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);

glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
// equivalent to glutswapBuffers()
[context presentRenderbuffer:GL_RENDERBUFFER_OES];

/*********************SECOND VIEW*******/
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, defaultFramebuffer);
glViewport(backingWidth/2, 0, backingWidth/2, backingHeight/2);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(-1.0f, 1.0f, -1.5f, 1.5f, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);
glRotatef(3.0f, 0.0f, 0.0f, 1.0f);

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

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);

glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
/*********************END***************/

glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
  1. On the simulator, only the second viewport appears (in this case a rotating cube in the bottom right corner of screen). Whereas on the device they both appear but blinking... (top left AND bottom riht)
  2. the glRotatef gets applied twice, but I only want to or any other transformation to be applied once.

What i want is simply to show the same scene twice. Basically I'm trying to simulate having 2 cameras watching the same thing, and show this on the screen. Clearly, I'm doing something wrong, would it be better to have 2 separate framebuffers and renderbuffers or is there a simpler way of achieving this?

Upvotes: 0

Views: 1392

Answers (1)

XKpe
XKpe

Reputation: 80

The problem is this line:

/*********************SECOND VIEW*******/
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_FRAMEBUFFER);

glClear is not affected by the viewport, you need to use either the scissors test or the stencil buffer if you want to partially clear.

See the documentation for glClear.

Upvotes: 2

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