Best way to initialize values on 32-bit FP framebuffer in OpenGL

Question

I have a framebuffer bound to 32-bit FP texture:

glGenTextures(1, &texColor);
glBindTexture(GL_TEXTURE_2D, texColor);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, w, h, 0, GL_RGBA, GL_FLOAT, (GLvoid*)NULL);
glBindTexture(GL_TEXTURE_2D, 0);

glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texColor, 0);

What's the best way to initialize framebuffer to a value 1000.0?

The problem is that

glClearColor(1000.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);

clamps values to [0,1] interval, and clearing the texture texColor would require memory allocation of w * h * sizeof(float) bytes of memory and manual filling of that buffer with value 1000.0 which is slow (I would inject it using glTexImage2D).

I'm using OpenGL 3.2 Core profile.

Thanks, Josip

Answer 1

You can render a quad onto the framebuffer with a shader that will just set the color value to 1000.0.

Since you don't even need to set a texture really let alone compute lighting, this should not really take any noteworthy time to accomplish.

It's pretty easy to do but here is a tutorial that talks about rendering to a texture. Though really you don't even need to do all of those steps.

http://www.learnopengl.com/#!Advanced-OpenGL/Framebuffers