RE: Signed colour values and clamping

Yes, colors are clamped to [0,1] in Section 2.14.6 in the OpenGL 2.0
spec.  I believe that there is a register combiner input mode that can
take values in the range [0,1] and map them to [-1,+1], or possibly
[-1/2, +1/2] in conjunction with a scale by half.

 

ARB_color_buffer_float provides a control that relaxes this clamping
plus clamping for fragment processing operations, for use with
floating-point color buffers.  I'm not sure that we've properly
documented the interaction of ARB_color_buffer_float and
NV_register_combiners.  I'm 95% certain that the approach we chose was
that register combiners continued to operate with clamped values.

 

Pat

 

________________________________

Robin Charlton
Sent: Monday, April 10, 2006 10:54 AM
To: Multiple recipients of list OPENGL-GAMEDEV-L

 

I'd like to use signed vertex colour values in the range -0.5 to 0.5
with an additive texture stage to create high-lights and low-lights.
Unfortunately it seems that the colour values are clamped in the range 0
to 1 before input to the register-combiner.

 

The documentation says Neither floating-point nor signed integer values
are clamped to the range [0,1] before updating the current color.
However, color components are clamped to this range before they are
interpolated or written into a color buffer.

 

Is what I'm seeing consistent with the docs and expected behavour?

 

Thanks

__________________________________________________________
Robin E. Charlton                   [email protected]

 


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