Name ARB_texture_env_combine Name Strings GL_ARB_texture_env_combine Contact Bimal Poddar, Intel (bimal.poddar 'at' intel.com) Michael Gold, NVIDIA (gold 'at' nvidia.com) Tom Frisinger, AMD (tom.frisinger 'at' amd.com) Rick Hammerstone, AMD (rick.hammerstone 'at' amd.com) Notice Copyright (c) 2001-2013 The Khronos Group Inc. Copyright terms at http://www.khronos.org/registry/speccopyright.html Status Complete. Approved by ARB on February 16, 2001. Version Last modified date: 2006/11/04 Number ARB Extension #17 Dependencies This extension is written against the OpenGL 1.2.1 Specification. OpenGL 1.1 and ARB_multitexture are required for this extension. Overview New texture environment function COMBINE_ARB allows programmable texture combiner operations, including: REPLACE Arg0 MODULATE Arg0 * Arg1 ADD Arg0 + Arg1 ADD_SIGNED_ARB Arg0 + Arg1 - 0.5 SUBTRACT_ARB Arg0 - Arg1 INTERPOLATE_ARB Arg0 * (Arg2) + Arg1 * (1-Arg2) where Arg0, Arg1 and Arg2 are derived from PRIMARY_COLOR_ARB primary color of incoming fragment TEXTURE texture color of corresponding texture unit CONSTANT_ARB texture environment constant color PREVIOUS_ARB result of previous texture environment; on texture unit 0, this maps to PRIMARY_COLOR_ARB In addition, the result may be scaled by 1.0, 2.0 or 4.0. Issues 1. Should the explicit bias be removed in favor of an implcit bias as part of a ADD_SIGNED_ARB function? - RESOLVED: Yes. This pre-scale bias is a special case and will be treated as such. 2. Should the primary color of the incoming fragment be available to all texture environments? Currently it is only available to the texture environment of texture unit 0. - RESOLVED: Yes. PRIMARY_COLOR_ARB has been added as an input source. 3. Should textures from other texture units be allowed as sources? - RESOLVED: NO. Even though this adds a lot of flexibility that folks can use today, there is not enough support amonst the ARB participants to add it to the base spec. 4. All of the 1.2 modes except BLEND can be expressed in terms of this extension. Should texture color be allowed as a source for Arg2, so all of the 1.2 modes can be expressed? If so, should all color sources be allowed, to maintain orthogonality? - RESOLVED: Yes. This seems to be a reasonable area to expand functionality and remain backwards compatible with the EXT version of the extension. 5. If the texture environment for a given texture unit does not reference the texture object that is bound to that texture unit, does a valid texture object need to be bound that unit? - RESOLVED: Yes. Each texture unit implicitly references the texture object that is bound to that unit, regardless of the texture environment function. This may require that applications bind a dummy texture to the texture unit. 6. Should we allow the secondary color to take part in texture blending? - RESOLVED: Not in this extension. Secondary color was defined as a specular part of the lit color and does not have associated alpha. In order to do this right, the secondary color extension needs to be fixed first to allow a full featured color and clearly state the interaction of how it interacts with the color sum stage. 7. How exactly is this ARB extension different from the EXT version? - RESOLVED: 1) This extension adds the GL_SUBTRACT_ARB mode 2) OPERAND2_RGB_ARB can use SRC_COLOR, ONE_MINUS_SRC_COLOR, SRC_ALPHA, and ONE_MINUS_SRC_ALPHA instead of just SRC_ALPHA (NV_texture_env_combine4 already provides this). 3) OPERAND2_ALPHA_ARB can use SRC_ALPHA and ONE_MINUS_SRC_ALPHA instead of just SRC_ALPHA (NV_texture_env_combine4 already provides this). New Procedures and Functions None New Tokens Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is TEXTURE_ENV_MODE COMBINE_ARB 0x8570 Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is TEXTURE_ENV COMBINE_RGB_ARB 0x8571 COMBINE_ALPHA_ARB 0x8572 SOURCE0_RGB_ARB 0x8580 SOURCE1_RGB_ARB 0x8581 SOURCE2_RGB_ARB 0x8582 SOURCE0_ALPHA_ARB 0x8588 SOURCE1_ALPHA_ARB 0x8589 SOURCE2_ALPHA_ARB 0x858A OPERAND0_RGB_ARB 0x8590 OPERAND1_RGB_ARB 0x8591 OPERAND2_RGB_ARB 0x8592 OPERAND0_ALPHA_ARB 0x8598 OPERAND1_ALPHA_ARB 0x8599 OPERAND2_ALPHA_ARB 0x859A RGB_SCALE_ARB 0x8573 ALPHA_SCALE Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is COMBINE_RGB_ARB or COMBINE_ALPHA_ARB REPLACE MODULATE ADD ADD_SIGNED_ARB 0x8574 INTERPOLATE_ARB 0x8575 SUBTRACT_ARB 0x84E7 Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is SOURCE0_RGB_ARB, SOURCE1_RGB_ARB, SOURCE2_RGB_ARB, SOURCE0_ALPHA_ARB, SOURCE1_ALPHA_ARB, or SOURCE2_ALPHA_ARB TEXTURE CONSTANT_ARB 0x8576 PRIMARY_COLOR_ARB 0x8577 PREVIOUS_ARB 0x8578 Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is OPERAND0_RGB_ARB, OPERAND1_RGB_ARB, or OPERAND2_RGB_ARB SRC_COLOR ONE_MINUS_SRC_COLOR SRC_ALPHA ONE_MINUS_SRC_ALPHA Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is OPERAND0_ALPHA_ARB, OPERAND1_ALPHA_ARB, or OPERAND2_ALPHA_ARB SRC_ALPHA ONE_MINUS_SRC_ALPHA Accepted by the parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnviv when the parameter value is RGB_SCALE_ARB or ALPHA_SCALE 1.0 2.0 4.0 Additions to Chapter 2 of the GL Specification (OpenGL Operation) None Additions to Chapter 3 of the GL Specification (Rasterization) Added to subsection 3.8.9, before the paragraph describing the state requirements: If the value of TEXTURE_ENV_MODE is COMBINE_ARB, the form of the texture function depends on the values of COMBINE_RGB_ARB and COMBINE_ALPHA_ARB, according to table 3.20. The RGB and ALPHA results of the texture function are then multiplied by the values of RGB_SCALE_ARB and ALPHA_SCALE, respectively. The results are clamped to [0,1]. COMBINE_RGB_ARB Texture Function ------------------ ---------------- REPLACE Arg0 MODULATE Arg0 * Arg1 ADD Arg0 + Arg1 ADD_SIGNED_ARB Arg0 + Arg1 - 0.5 INTERPOLATE_ARB Arg0 * (Arg2) + Arg1 * (1-Arg2) SUBTRACT_ARB Arg0 - Arg1 COMBINE_ALPHA_ARB Texture Function ------------------ ---------------- REPLACE Arg0 MODULATE Arg0 * Arg1 ADD Arg0 + Arg1 ADD_SIGNED_ARB Arg0 + Arg1 - 0.5 INTERPOLATE_ARB Arg0 * (Arg2) + Arg1 * (1-Arg2) SUBTRACT_ARB Arg0 - Arg1 Table 3.20: COMBINE_ARB texture functions The arguments Arg0, Arg1 and Arg2 are determined by the values of SOURCE_RGB_ARB, SOURCE_ALPHA_ARB, OPERAND_RGB_ARB and OPERAND_ALPHA_ARB. In the following two tables, Ct and At are the filtered texture RGB and alpha values; Cc and Ac are the texture environment RGB and alpha values; Cf and Af are the RGB and alpha of the primary color of the incoming fragment; and Cp and Ap are the RGB and alpha values resulting from the previous texture environment. On texture environment 0, Cp and Ap are identical to Cf and Af, respectively. The relationship is described in tables 3.21 and 3.22. SOURCE_RGB_ARB OPERAND_RGB_ARB Argument ----------------- -------------- -------- TEXTURE SRC_COLOR Ct ONE_MINUS_SRC_COLOR (1-Ct) SRC_ALPHA At ONE_MINUS_SRC_ALPHA (1-At) CONSTANT_ARB SRC_COLOR Cc ONE_MINUS_SRC_COLOR (1-Cc) SRC_ALPHA Ac ONE_MINUS_SRC_ALPHA (1-Ac) PRIMARY_COLOR_ARB SRC_COLOR Cf ONE_MINUS_SRC_COLOR (1-Cf) SRC_ALPHA Af ONE_MINUS_SRC_ALPHA (1-Af) PREVIOUS_ARB SRC_COLOR Cp ONE_MINUS_SRC_COLOR (1-Cp) SRC_ALPHA Ap ONE_MINUS_SRC_ALPHA (1-Ap) Table 3.21: Arguments for COMBINE_RGB_ARB functions SOURCE_ALPHA_ARB OPERAND_ALPHA_ARB Argument ----------------- -------------- -------- TEXTURE SRC_ALPHA At ONE_MINUS_SRC_ALPHA (1-At) CONSTANT_ARB SRC_ALPHA Ac ONE_MINUS_SRC_ALPHA (1-Ac) PRIMARY_COLOR_ARB SRC_ALPHA Af ONE_MINUS_SRC_ALPHA (1-Af) PREVIOUS_ARB SRC_ALPHA Ap ONE_MINUS_SRC_ALPHA (1-Ap) Table 3.22: Arguments for COMBINE_ALPHA_ARB functions The mapping of texture components to source components is summarized in Table 3.23. In the following table, At, Lt, It, Rt, Gt and Bt are the filtered texel values. Base Internal Format RGB Values Alpha Value -------------------- ---------- ----------- ALPHA 0, 0, 0 At LUMINANCE Lt, Lt, Lt 1 LUMINANCE_ALPHA Lt, Lt, Lt At INTENSITY It, It, It It RGB Rt, Gt, Bt 1 RGBA Rt, Gt, Bt At Table 3.23: Correspondence of texture components to source components for COMBINE_RGB_ARB and COMBINE_ALPHA_ARB arguments Additions to Chapter 4 of the GL Specification (Per-Fragment Operations and the Framebuffer) None Additions to Chapter 5 of the GL Specification (Special Functions) None Additions to Chapter 6 of the GL Specification (State and State Requests) None Additions to Appendix F of the GL Specification (ARB Extensions) Inserted after the second paragraph of F.2.12: If the value of TEXTURE_ENV_MODE is COMBINE_ARB, the texture function associated with a given texture unit is computed using the values specified by SOURCE_RGB_ARB, SOURCE_ALPHA_ARB, OPERAND_RGB_ARB and OPERAND_ALPHA_ARB. If TEXTURE_ARB is specified as SOURCE_RGB_ARB or SOURCE_ALPHA_ARB, the texture value from texture unit will be used in computing the texture function for this texture unit. Inserted after the third paragraph of F.2.12: If a texture environment for a given texture unit references a texture unit that is disabled or does not have a valid texture object bound to it, then it is as if texture is disabled for the given texture unit. Every texture unit implicitly references the texture object that is bound to it, regardless of the texture function specified by COMBINE_RGB_ARB or COMBINE_ALPHA_ARB. Additions to the GLX Specification None GLX Protocol None Errors INVALID_ENUM is generated if value for COMBINE_RGB_ARB or COMBINE_ALPHA_ARB is not one of REPLACE, MODULATE, ADD, ADD_SIGNED_ARB, INTERPOLATE_ARB, or SUBTRACT_ARB INVALID_ENUM is generated if value for SOURCE0_RGB_ARB, SOURCE1_RGB_ARB, SOURCE2_RGB_ARB, SOURCE0_ALPHA_ARB, SOURCE1_ALPHA_ARB or SOURCE2_ALPHA_ARB is not one of TEXTURE, CONSTANT_ARB, PRIMARY_COLOR_ARB, or PREVIOUS_ARB. INVALID_ENUM is generated if value for OPERAND0_RGB_ARB, OPERAND1_RGB_ARB, or OPERAND2_RGB_ARB is not one of SRC_COLOR, ONE_MINUS_SRC_COLOR, SRC_ALPHA or ONE_MINUS_SRC_ALPHA. INVALID_ENUM is generated if value for OPERAND0_ALPHA_ARB, OPERAND1_ALPHA_ARB, or OPERAND2_ALPHA_ARB is not one of SRC_ALPHA or ONE_MINUS_SRC_ALPHA. INVALID_VALUE is generated if value for RGB_SCALE_ARB or ALPHA_SCALE is not one of 1.0, 2.0, or 4.0. New State Get Value Get Command Type Initial Value Attribute --------- ----------- ---- ------------- --------- COMBINE_RGB_ARB GetTexEnviv n x Z4 MODULATE texture COMBINE_ALPHA_ARB GetTexEnviv n x Z4 MODULATE texture SOURCE0_RGB_ARB GetTexEnviv n x Z3 TEXTURE texture SOURCE1_RGB_ARB GetTexEnviv n x Z3 PREVIOUS_ARB texture SOURCE2_RGB_ARB GetTexEnviv n x Z3 CONSTANT_ARB texture SOURCE0_ALPHA_ARB GetTexEnviv n x Z3 TEXTURE texture SOURCE1_ALPHA_ARB GetTexEnviv n x Z3 PREVIOUS_ARB texture SOURCE2_ALPHA_ARB GetTexEnviv n x Z3 CONSTANT_ARB texture OPERAND0_RGB_ARB GetTexEnviv n x Z6 SRC_COLOR texture OPERAND1_RGB_ARB GetTexEnviv n x Z6 SRC_COLOR texture OPERAND2_RGB_ARB GetTexEnviv n x Z1 SRC_ALPHA texture OPERAND0_ALPHA_ARB GetTexEnviv n x Z4 SRC_ALPHA texture OPERAND1_ALPHA_ARB GetTexEnviv n x Z4 SRC_ALPHA texture OPERAND2_ALPHA_ARB GetTexEnviv n x Z1 SRC_ALPHA texture RGB_SCALE_ARB GetTexEnvfv n x R3 1.0 texture ALPHA_SCALE GetTexEnvfv n x R3 1.0 texture New Implementation Dependent State None Revision History 06/11/04 benj Updated contact info after ATI/AMD merger. 01/05/21 mjk Added ARB versus EXT differences issue 01/02/02 bpoddar Added original EXT/ARB contributors to the contact list 00/12/13 bpoddar Added enum value for SUBTRACT_ARB 00/12/06 bpoddar Moved references to Ct and At to ARB_texture_env_crossbar spec. 00/12/01 bpoddar Removed TEXTURE_ARB since several companies had problems with this addition in the base spec. 00/11/13 bpoddar Recreated 6/20 spec with language for dealing with inconsistent textures moved to appendix F. 00/06/20 rhammers Changed behavior when dealing with references do disabled and inconsistent textures. 00/05/23 rhammers Cleaned up for first draft of ARB version. Added issue -- TEXTURE with TEXTURE_ARB Added issue .. "upstream" textures Listed get functions with description of enumerants. Added 1.1 and multitexture to dependencies 00/05/18 rhammers First rev of ARB version of the spec. Based on EXT_texture_env_combine. Relaxed restriction on Arg2. Added support for TEXTURE_ARB. Added SUBTRACT_ARB combiner function. do disabled and inconsistent textures.