OpenGL ES Render to Texture

Question

I have been having trouble finding straightforward code to render a scene to a texture in OpenGL ES (specifically for the iPhone, if that matters). I am interested in knowin

Answer 1

To render the scene to a texture you must use a framebuffer associated with a texture. Here is a method that i created to simplify it :

void glGenTextureFromFramebuffer(GLuint *t, GLuint *f, GLsizei w, GLsizei h)
{
    glGenFramebuffers(1, f);
    glGenTextures(1, t);

    glBindFramebuffer(GL_FRAMEBUFFER, *f);

    glBindTexture(GL_TEXTURE_2D, *t);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, *t, 0);

    GLuint depthbuffer;
    glGenRenderbuffers(1, &depthbuffer);    
    glBindRenderbuffer(GL_RENDERBUFFER, depthbuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, w, h);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthbuffer);

    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(status != GL_FRAMEBUFFER_COMPLETE)
        NSLog(@"Framebuffer status: %x", (int)status);
}

You can create the frame buffer and the texture easily :

GLuint _texture, _framebuffer;
GLsizei w,h;
float scale = [UIScreen mainScreen].scale;
w = self.view.bounds.size.width * scale;
h = self.view.bounds.size.height * scale;
glGenTextureFromFramebuffer(&_texture, &_framebuffer, w, h);

You can later use _framebuffer to render the scene into _texture in your draw method :

glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
//draw here the content you want in the texture
//_texture is now a texture with the drawn content

//bind the base framebuffer
glBindFramebuffer(GL_FRAMEBUFFER, 0);
//or if you use GLKit
[view bindDrawable];
//draw normaly

Now you can do what you want with the texture. If you want to do some post processing (blur, bloom, shadow, etc...) you can !