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Name
NV_texgen_reflection
Name Strings
GL_NV_texgen_reflection
Contact
Mark J. Kilgard, NVIDIA Corporation (mjk 'at' nvidia.com)
Notice
Copyright NVIDIA Corporation, 1999.
Status
Shipping (version 1.0)
NVIDIA, Mesa 3.1, and ATI support this.
This extension's texture coordinate generation functionality is
incoporated into the ARB_texture_cube_map extension. The same
enumerant values are used.
The ARB_texture_cube_map functionality, including this texgen
reflection functionality, is part of OpenGL 1.3 and subsequent
revisions of the core OpenGL standard.
Version
June 17, 2003 (version 1.0)
Number
179
Dependencies
Written based on the wording of the OpenGL 1.2 specification but
not dependent on it.
Overview
This extension provides two new texture coordinate generation modes
that are useful texture-based lighting and environment mapping.
The reflection map mode generates texture coordinates (s,t,r)
matching the vertex's eye-space reflection vector. The reflection
map mode is useful for environment mapping without the singularity
inherent in sphere mapping. The normal map mode generates texture
coordinates (s,t,r) matching the vertex's transformed eye-space
normal. The normal map mode is useful for sophisticated cube map
texturing-based diffuse lighting models.
Issues
Should we place the normal/reflection vector in the (s,t,r) texture
coordinates or (s,t,q) coordinates?
RESOLUTION: (s,t,r). Even if the proposed hardware uses "q" for
the third component, the API should claim to support generation of
(s,t,r) and let the texture matrix (through a concatenation with
the user-supplied texture matrix) move "r" into "q".
Should you be able to have some texture coordinates computing
REFLECTION_MAP_NV and others not? Same question with NORMAL_MAP_NV.
RESOLUTION: YES. This is the way that SPHERE_MAP works. It is
not clear that this would ever be useful though.
Should something special be said about the handling of the q
texture coordinate for this spec?
RESOLUTION: NO. But the following paragraph is useful for
implementors concerned about the handling of q.
The REFLECTION_MAP_NV and NORMAL_MAP_NV modes are intended to supply
reflection and normal vectors for cube map texturing hardware.
When these modes are used for cube map texturing, the generated
texture coordinates can be thought of as a reflection vector.
The value of the q texture coordinate then simply scales the
vector but does not change its direction. Because only the vector
direction (not the vector magnitude) matters for cube map texturing,
implementations are free to leave q undefined when any of the s,
t, or r texture coordinates are generated using REFLECTION_MAP_NV
or NORMAL_MAP_NV.
New Procedures and Functions
None
New Tokens
Accepted by the <param> parameters of TexGend, TexGenf, and TexGeni
when <pname> parameter is TEXTURE_GEN_MODE:
NORMAL_MAP_NV 0x8511
REFLECTION_MAP_NV 0x8512
When the <pname> parameter of TexGendv, TexGenfv, and TexGeniv is
TEXTURE_GEN_MODE, then the array <params> may also contain
NORMAL_MAP_NV or REFLECTION_MAP_NV.
Additions to Chapter 2 of the 1.2 Specification (OpenGL Operation)
-- Section 2.10.4 "Generating Texture Coordinates"
Change the last sentence in the 1st paragraph to:
"If <pname> is TEXTURE_GEN_MODE, then either <params> points to
or <param> is an integer that is one of the symbolic constants
OBJECT_LINEAR, EYE_LINEAR, SPHERE_MAP, REFLECTION_MAP_NV, or
NORMAL_MAP_NV."
Add these paragraphs after the 4th paragraph:
"If TEXTURE_GEN_MODE indicates REFLECTION_MAP_NV, compute the
reflection vector r as described for the SPHERE_MAP mode. Then the
value assigned to an s coordinate (the first TexGen argument value
is S) is s = rx; the value assigned to a t coordinate is t = ry;
and the value assigned to a r coordinate is r = rz. Calling TexGen
with a <coord> of Q when <pname> indicates REFLECTION_MAP_NV
generates the error INVALID_ENUM.
If TEXTURE_GEN_MODE indicates NORMAL_MAP_NV, compute the normal
vector n' as described in section 2.10.3. Then the value assigned
to an s coordinate (the first TexGen argument value is S) is s =
nfx; the value assigned to a t coordinate is t = nfy; and the
value assigned to a r coordinate is r = nfz. (The values nfx, nfy,
and nfz are the components of nf.) Calling TexGen with a <coord>
of Q when <pname> indicates REFLECTION_MAP_NV generates the error
INVALID_ENUM.
The last paragraph's first sentence should be changed to:
"The state required for texture coordinate generation comprises a
five-valued integer for each coordinate indicating coordinate
generation mode, ..."
Additions to Chapter 3 of the 1.2 Specification (Rasterization)
None
Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations
and the Frame Buffer)
None
Additions to Chapter 5 of the 1.2 Specification (Special Functions)
None
Additions to Chapter 6 of the 1.2 Specification (State and State Requests)
None
Additions to the GLX Specification
None
Errors
INVALID_ENUM is generated when TexGen is called with a <coord> of Q
when <pname> indicates REFLECTION_MAP_NV or NORMAL_MAP_NV.
New State
(table 6.14, p204) change the entry for TEXTURE_GEN_MODE to:
Get Value Type Get Command Initial Value Description Sec Attribute
--------- ---- ----------- ------------- ----------- ------ ---------
TEXTURE_GEN_MODE 4xZ5 GetTexGeniv EYE_LINEAR Function used for 2.10.4 texture
texgen (for s,t,r,
and q)
(the type changes from 4xZ3 to 4xZ5)
New Implementation State
None
Revision History
None