Question

I am trying to write a view space position out through gl_FragData.

Unfortunately this value seems to be clamped [0-1]
(or at least it is when I read it back)

Is there a way not to clamp it?

Answer 1

Simply use floating point textures: GL_RGBA16F, GL_RGBA32F, etc… they are not clamped

http://www.opengl.org/wiki/Floating_point_and_mipmapping_and_filtering

I use (for creating empty floating point texture):

glGenTextures(1, &texId);
glBindTexture(GL_TEXTURE_2D, texId);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);        
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);    
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);   
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB16F, width, height, 0, GL_RGB, GL_FLOAT, NULL);