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Name Strings
Mark J. Kilgard, NVIDIA Corporation (mjk 'at'
Thomas Roell
Copyright NVIDIA Corporation, 2000, 2001, 2004.
IP Status
NVIDIA Proprietary.
NVIDIA Date: December 13, 2004
Version 1.2
Written based on the wording of the OpenGL 1.2.1 specification.
Assumes support for the NV_register_combiners extension (version 1.4).
The NV_register_combiners extension provides a powerful fragment
coloring mechanism. This specification extends the register combiners
functionality to support more color constant values that are unique
for each general combiner stage.
The base register combiners functionality supports only two color
constants. These two constants are available in every general
combiner stage and in the final combiner.
When many general combiner stages are supported, more than two
unique color constants is often required. The obvious way to extend
the register combiners is to add several more color constant
registers. But adding new unique color constant registers is
expensive for hardware implementation because every color constant
register must be available as an input to any stage.
In practice however, it is the total set of general combiner stages
that requires more color constants, not each and every individual
general combiner stage. Each individual general combiner stage
typically requires only one or two color constants.
By keeping two color constant registers but making these two registers
contain two unique color constant values for each general combiner
stage, the hardware expense of supporting multiple color constants
is minimized. Additionally, this scheme scales appropriately as
more general combiner stages are added.
How do is compatibility maintained with the original register
RESOLUTION: Initially, per general combiner stage constants are
disabled and the register combiners operate as described in the
original NV_register_combiners specification. A distinct "per
stage constants" enable exposes this extension's new functionality.
Where do the final combiner color constant values come from?
RESOLUTION: When "per stage constants" is enabled, the final
combiner color constants continue to use the constant colors set
with glCombinerParameterfvNV.
Is the alpha component of the SECONDARY_COLOR_NV register now
initialized with the expected interpolated secondary color's alpha
RESOLUTION: Yes, see Revision History for details.
New Procedures and Functions
void CombinerStageParameterfvNV(GLenum stage,
GLenum pname,
const GLfloat *params);
void GetCombinerStageParameterfvNV(GLenum stage,
GLenum pname,
GLfloat *params);
New Tokens
Accepted by the <cap> parameter of Disable, Enable, and IsEnabled,
and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv,
and GetDoublev:
Accepted by the <pname> parameter of CombinerStageParameterfvNV
and GetCombinerStageParameterfvNV:
CONSTANT_COLOR0_NV (see NV_register_combiners)
CONSTANT_COLOR1_NV (see NV_register_combiners)
Accepted by the <stage> parameter of CombinerStageParameterfvNV and
COMBINER0_NV (see NV_register_combiners)
COMBINER1_NV (see NV_register_combiners)
COMBINER2_NV (see NV_register_combiners)
COMBINER3_NV (see NV_register_combiners)
COMBINER4_NV (see NV_register_combiners)
COMBINER5_NV (see NV_register_combiners)
COMBINER6_NV (see NV_register_combiners)
COMBINER7_NV (see NV_register_combiners)
Additions to Chapter 2 of the 1.2 Specification (OpenGL Operation)
Additions to Chapter 3 of the 1.2 Specification (Rasterization)
-- Section 3.8.12 "Register Combiners Application"
Because the alpha component of the SECONDARY_COLOR_NV register is
well-defined now (see Revision History) to be the alpha value of csec,
STRIKE this sentence:
"The initial value of the alpha portion of register SECONDARY_COLOR_NV
is undefined."
Add a paragraph immediately before section
"The ccc0 and ccc1 values map to particular constant color values.
The ccc0 and ccc1 mappings depend on whether per-stage constants
are enabled or not. Per-stage constants are enabled and disabled
with the Enable and Disable commands using the symbolic constant
When per-stage constants are disabled, ccc0 and ccc1 are mapped to
the register combiners' global color constant values, gccc0 and
When per-stage constants are enabled, ccc0 and ccc1 depend
on the combiner stage that inputs the COLOR_CONSTANT0_NV and
COLOR_CONSTANT1_NV registers. Each general combiner stage # maps
ccc0 and ccc1 to the per-stage values s#ccc0 and s#ccc1 respectively.
The final combiner maps ccc0 and ccc1 to the values gccc0 and gccc1
(the same as if per-stage constants are disabled).
gccc0, gccc1, s#ccc0, and s#ccc1 are further described in the
following section."
-- Section "Combiner Parameters"
Change Table NV_register_combiners.3 to read "gccc0" instead of
"ccc0" and "gccc1" instead of "ccc1".
Change the first sentence of the last paragraph to read:
"The values gccc0 and gccc1 named by CONSTANT_COLOR0_NV and
CONSTANT_COLOR1_NV are global constant colors available for inputs to
the final combiner stage and, when per-stage constants is disabled,
to the general combiner stages."
Add the following after the last paragraph in the section:
"Per-stage combiner parameters are specified by
void CombinerStageParameterfvNV(GLenum stage,
GLenum pname,
const GLfloat *params);
The <stage> parameter is a symbolic constant of the form
COMBINER<#>_NV, indicating the general combiner stage <#> whose
parameter named by <pname> is to be updated. <pname> must be either
CONSTANT_COLOR0_NV or CONSTANT_COLOR1_NV. <params> is a pointer
to a group of four values to which to set the indicated parameter.
update the per-stage color constants s#ccc0 and s#ccc1 respectively
where # is the number of the specified general combiner stage.
The floating-point color values are clamped to the range [0,1]
when specified."
Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations
and the Frame Buffer)
Additions to Chapter 5 of the 1.2 Specification (Special Functions)
Additions to Chapter 6 of the 1.2 Specification (State and State Requests)
-- Section 6.1.3 "Enumerated Queries"
Add to the bottom of the list of function prototypes (page 183):
void GetCombinerStageParameterfvNV(GLenum stage,
GLenum pname,
GLfloat *params);
Change the first sentence describing the register combiner queries
to mention GetCombinerStageParameterfvNV so the sentence reads:
"The GetCombinerInputParameterfvNV, GetCombinerInputParameterivNV,
GetCombinerOutputParameterfvNV, GetCombinerOutputParameterivNV,
and GetCombinerStageParameterfvNV parameter <stage> may be one of
COMBINER0_NV, COMBINER1_NV, and so on, indicating which general
combiner stage to query."
Additions to the GLX Specification
GLX Protocol
Two new GL commands are added.
The following rendering command is sent to the sever as part of a
glXRender request:
2 12+4*n rendering command length
2 4280 rendering command opcode
4 ENUM stage
4 ENUM pname
else n=0
4*n LISTofFLOAT32 params
The remaining command is a non-rendering command. This commands
is sent separately (i.e., not as part of a glXRender or glXRenderLarge
request), using the glXVendorPrivateWithReply request:
1 CARD8 opcode (X assigned)
1 17 GLX opcode (glXVendorPrivateWithReply)
2 5 request length
4 1327 vendor specific opcode
4 GLX_CONTEXT_TAG context tag
4 ENUM stage
4 ENUM pname
1 1 reply
1 unused
2 CARD16 sequence number
4 m reply length, m = (n==1 ? 0 : n)
4 unused
4 CARD32 unused
if (n=1) this follows:
4 FLOAT32 params
12 unused
otherwise this follows:
16 unused
n*4 LISTofFLOAT32 params
New State
Get Value Type Get Command Initial Value Description Sec Attribute
---------------------- ---- ----------------------------- ------------- ------------------ -------- --------------
PER_STAGE_CONSTANTS_NV B IsEnabled False enable for 3.8.12 texture/enable
CONSTANT_COLOR0_NV Cx# GetCombinerStageParameterfvNV 0,0,0,0 per-stage constant texture
color zero
CONSTANT_COLOR1_NV Cx# GetCombinerStageParameterfvNV 0,0,0,0 per-stage constant texture
color one
[ where # is the value of MAX_GENERAL_COMBINERS_NV ]
New Implementation State
Revision History
December 13, 2004: Assigned GLX protocl opcodes and fixed protocol
with help from Thomas Roell.
Version 1.2 (February 11, 2004) - When describing the
per-fragment register initialization within the combiners, the
NV_register_combiners specification says "The initial value of the
alpha portion of register SECONDARY_COLOR_NV is undefined." While
this is true of NV1x GPUs, NV2x and beyond GPUs can properly
initialize the alpha component of the SECONDARY_COLOR_NV
register with the expected interpolated secondary color alpha.
Unfortunately, due to a driver bug, the alpha components was always
initialized to 1.0 in driver versions 56.90 (circa February 2004)
and before. Drivers subsequent to 56.90 have this problem fixed.
This specification is updated to indicate that SECONDARY_COLOR_NV
initialization is well-defined and what you would expect now.
Version 1.1 (April 28, 2003) - The original specification failed
to specify what should happen if a color component parameter for
CombinerStageParameter*NV is outside the [0,1] range. Such values
should be clamped to the [0,1] range.
NVIDIA drivers prior to May 2003 incorrectly failed to clamp color
component values specified with CombinerStageParameter*NV to [0,1].
Instead, approximately "x-floor(x)" where x is a component value
is used for rendering.