| Name |
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| NV_register_combiners2 |
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| Name Strings |
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| GL_NV_register_combiners2 |
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| Contact |
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| Mark J. Kilgard, NVIDIA Corporation (mjk 'at' nvidia.com) |
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| Contributors |
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| Thomas Roell |
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| Notice |
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| Copyright NVIDIA Corporation, 2000, 2001, 2004. |
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| IP Status |
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| NVIDIA Proprietary. |
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| Status |
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| Implemented. |
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| Version |
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| NVIDIA Date: December 13, 2004 |
| Version 1.2 |
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| Number |
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| 227 |
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| Dependencies |
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| Written based on the wording of the OpenGL 1.2.1 specification. |
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| Assumes support for the NV_register_combiners extension (version 1.4). |
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| Overview |
| |
| 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. |
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| Issues |
| |
| How do is compatibility maintained with the original register |
| combiners? |
| |
| 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? |
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| 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 |
| component. |
| |
| RESOLUTION: Yes, see Revision History for details. |
| |
| New Procedures and Functions |
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| void CombinerStageParameterfvNV(GLenum stage, |
| GLenum pname, |
| const GLfloat *params); |
| |
| void GetCombinerStageParameterfvNV(GLenum stage, |
| GLenum pname, |
| GLfloat *params); |
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| New Tokens |
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| Accepted by the <cap> parameter of Disable, Enable, and IsEnabled, |
| and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, |
| and GetDoublev: |
| |
| PER_STAGE_CONSTANTS_NV 0x8535 |
| |
| Accepted by the <pname> parameter of CombinerStageParameterfvNV |
| and GetCombinerStageParameterfvNV: |
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| CONSTANT_COLOR0_NV (see NV_register_combiners) |
| CONSTANT_COLOR1_NV (see NV_register_combiners) |
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| Accepted by the <stage> parameter of CombinerStageParameterfvNV and |
| GetCombinerStageParameterfvNV: |
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| 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) |
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| None |
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| 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 3.8.12.1: |
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| "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 |
| PER_STAGE_CONSTANTS_NV. |
| |
| When per-stage constants are disabled, ccc0 and ccc1 are mapped to |
| the register combiners' global color constant values, gccc0 and |
| gccc1. |
| |
| 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 3.8.12.1 "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 |
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| 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. |
| The parameter names CONSTANT_COLOR0_NV and CONSTANT_COLOR1_NV |
| 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) |
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| None |
| |
| Additions to Chapter 5 of the 1.2 Specification (Special Functions) |
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| None |
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| Additions to Chapter 6 of the 1.2 Specification (State and State Requests) |
| |
| -- Section 6.1.3 "Enumerated Queries" |
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| 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 |
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| None |
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| GLX Protocol |
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| Two new GL commands are added. |
| |
| The following rendering command is sent to the sever as part of a |
| glXRender request: |
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| CombinerStageParameterfvNV |
| 2 12+4*n rendering command length |
| 2 4280 rendering command opcode |
| 4 ENUM stage |
| 4 ENUM pname |
| 0x852A n=4 GL_CONSANT_COLOR0_NV |
| 0x852B n=4 GL_CONSANT_COLOR1_NV |
| 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: |
| |
| GetCombinerStageParameterfvNV |
| 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 |
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| if (n=1) this follows: |
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| 4 FLOAT32 params |
| 12 unused |
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| otherwise this follows: |
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| 16 unused |
| n*4 LISTofFLOAT32 params |
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| Errors |
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| None |
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| New State |
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| 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 3.8.12.1 texture |
| color zero |
| CONSTANT_COLOR1_NV Cx# GetCombinerStageParameterfvNV 0,0,0,0 per-stage constant 3.8.12.1 texture |
| color one |
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| [ where # is the value of MAX_GENERAL_COMBINERS_NV ] |
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| New Implementation State |
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| None |
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| Revision History |
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| 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. |
