RE: Signed colour values and clamping

GL_NV_register_combiners seems to offer functionality similar to what
you describe.
 
Thanks for the help!
-
Robin

________________________________

	From: [email protected] [mailto:[email protected]] On
Behalf Of Pat Brown (OpenGL)
	Sent: 10 April 2006 16:29
	To: Multiple recipients of list OPENGL-GAMEDEV-L
	Subject: 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

	

	
________________________________


	From: [email protected] [mailto:[email protected]] On
Behalf Of Robin Charlton
	Sent: Monday, April 10, 2006 10:54 AM
	To: Multiple recipients of list OPENGL-GAMEDEV-L
	Subject: Signed colour values and clamping

	

	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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