| Name |
| |
| NV_blend_minmax_factor |
| |
| Name Strings |
| |
| GL_NV_blend_minmax_factor |
| |
| Contributors |
| |
| Jeff Bolz |
| Pierre Boudier |
| Charles Hansen |
| Bill Sebastian, Visual Music Systems |
| Graham Sellers, original AMD specification |
| |
| Contact |
| |
| Mark Kilgard, NVIDIA (mjk 'at' nvidia.com) |
| |
| Status |
| |
| Implemented in NVIDIA's August 2017 SIGGRAPH driver |
| |
| Version |
| |
| Last Modified Date: July 26, 2017 |
| Author Revision: 3 |
| |
| Number |
| |
| OpenGL Extension #510 |
| OpenGL ES Extension #285 |
| |
| Dependencies |
| |
| The extension is written against the OpenGL 4.1 (Core) Specification. |
| |
| OpenGL 1.0 or ES 2.0 is required. |
| |
| This extension interacts with |
| NVX_blend_equation_advanced_multi_draw_buffers as specified. |
| |
| This extension interacts with ARB_blend_func_extended, |
| EXT_blend_func_extended (for ES), or OpenGL 3.3 as specified. |
| |
| This extension interacts with NV_blend_equation_advanced, |
| NV_blend_equation_advanced_coherent, KHR_blend_equation_advanced, |
| KHR_blend_equation_advanced_coherent, OpenGL 4.5, or ES 3.2 as |
| specified. |
| |
| Overview |
| |
| The EXT_blend_minmax extension extended the GL's blending |
| functionality to allow the blending equation to be specified by the |
| application. That extension introduced the MIN_EXT and MAX_EXT blend |
| equations, which caused the result of the blend equation to become |
| the minimum or maximum of the source color and destination color, |
| respectively. |
| |
| The MIN_EXT and MAX_EXT blend equations, however, do not include the |
| source or destination blend factors in the arguments to the min and |
| max functions. This extension provides two new blend equations that |
| produce the minimum or maximum of the products of the source color |
| and source factor, and the destination color and destination factor. |
| |
| This NVIDIA extension has some limitations relative to the |
| AMD_blend_minmax_factor extension. See issues #1, #2, and #3. |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <mode> parameter of BlendEquation and BlendEquationi, and by |
| the <modeRGB> and <modeAlpha> parameters of BlendEquationSeparate and |
| BlendEquationSeparatei: |
| |
| FACTOR_MIN_AMD 0x901C |
| FACTOR_MAX_AMD 0x901D |
| |
| Additions to Chapter 2 of the OpenGL 4.1 (Core) Specification (OpenGL Operation) |
| |
| None. |
| |
| Additions to Chapter 3 of the OpenGL 4.1 (Core) Specification (Rasterization) |
| |
| None. |
| |
| Additions to Chapter 4 of the OpenGL 4.1 (Core) Specification (Per-Fragment |
| Operations and the Frame Buffer) |
| |
| Modify the list of accepted tokens for <mode>, <modeRGB> and <modeAlpha> |
| in the description of BlendEquation{i} and BlendEquationSeparate{i}, p.262: |
| |
| "... <mode>, <modeRGB>, <modeAlpha> must be one of FUNC_ADD, FUNC_SUBTRACT, |
| FUNC_REVERSE_SUBTRACT, MIN, MAX, FACTOR_MIN_AMD, or FACTOR_MAX_AMD. ..." |
| |
| Add to Table 4.1: RGB and Alpha Blend Equations |
| |
| +-----------------+---------------------------+-----------------------------+ |
| | Mode | RGB Components | Alpha Component | |
| +-----------------+---------------------------+-----------------------------+ |
| | FACTOR_MIN_AMD | R = min(Rs * Sr, Rd * Dr) | A = min(As * Sa, Ad * Da) | |
| | | G = min(Gs * Sg, Gd * Dg) | | |
| | | B = min(Bs * Sb, Bd * Db) | | |
| +-----------------+---------------------------+-----------------------------+ |
| | FACTOR_MAX_AMD | R = max(Rs * Sr, Rd * Dr) | A = max(As * Sa, Ad * Da) | |
| | | G = max(Gs * Sg, Gd * Dg) | | |
| | | B = max(Bs * Sb, Bd * Db) | | |
| +-----------------+---------------------------+-----------------------------+ |
| |
| Add the following precision limitation after table 4.1: |
| |
| "An implementation may perform the computations for the FACTOR_MIN_AMD |
| and FACTOR_MAX_AMD modes in half-precsion floating-point even |
| when the representable range of the framebuffer is can represent |
| single-precision or better color components." |
| |
| Add the following orthogonality restriction after table 4.1: |
| |
| "When the NVX_blend_equation_advanced_multi_draw_buffers is not |
| supported, the FACTOR_MIN_AMD and FACTOR_MAX_AMD blending equations |
| are supported only when rendering to a single color buffer using |
| fragment color zero. In this case, if any non-NONE draw buffer |
| enabled for blending uses either the FACTOR_MIN_AMD and FACTOR_MAX_AMD |
| blending equations, the error INVALID_OPERATION is generated by |
| [[Compatibility Profile: Begin or any operation that implicitly |
| calls Begin (such as DrawElements)]] [[Core Profile: DrawArrays |
| and the other drawing commands defined in section 2.8.3]] if: |
| |
| * the draw buffer for color output zero selects multiple color buffers |
| (e.g., FRONT_AND_BACK in the default framebuffer); or |
| |
| * the draw buffer for any other color output is not NONE. |
| |
| Alternatively when the NVX_blend_equation_advanced_multi_draw_buffers |
| is supported, if any non-NONE draw buffer enabled for blending uses |
| a blend equation of either FACTOR_MIN_AMD or FACTOR_MAX_AMD for |
| either RGB or alpha, the error INVALID_OPERATION is generated by |
| [[Compatibility Profile: Begin or any operation that implicitly |
| calls Begin (such as DrawElements)]] [[Core Profile: DrawArrays |
| and the other drawing commands defined in section 2.8.3]] if any |
| other non-NONE draw buffer uses a different combination of the |
| first draw buffer's RGB and alpha blend equation." In other words, |
| the FACTOR_MIN_AMD or FACTOR_MAX_AMD blend equations are now allowed |
| with multiple draw buffers as long as they use they use identical |
| blend equations for RGB and alpha for all non-NONE draw buffers. |
| |
| If any non-NONE draw buffer enabled for blending uses any of |
| SRC1_COLOR, SRC1_ALPHA, ONE_MINUS_SRC1_COLOR, or ONE_MINUS_SRC1_ALPHA |
| for a source or destination blend function, the error |
| INVALID_OPERATION is generated by [[Compatibility Profile: Begin or |
| any operation that implicitly calls Begin (such as DrawElements)]] |
| [[Core Profile: DrawArrays and the other drawing commands defined |
| in section 2.8.3]]." |
| |
| Additions to Chapter 5 of the OpenGL 4.1 (Core) Specification (Special Functions) |
| |
| None. |
| |
| Additions to Chapter 6 of the OpenGL 4.1 (Core) Specification (State and |
| State Requests) |
| |
| None. |
| |
| Additions to Appendix A of the OpenGL 4.1 (Core) Specification (Invariance) |
| |
| None. |
| |
| Additions to the AGL/GLX/WGL Specifications |
| |
| None. |
| |
| Errors |
| |
| None. |
| |
| New State |
| |
| Modify Table 6.21: Pixel Operations (cont.) p.343 |
| |
| Change entries for BLEND_EQUATION_ALPHA and BLEND_EQUATION_RGB to: |
| |
| +----------------------+---------+---------------+---------------+-------------------------+-------+ |
| | Get Value | Type | Get Command | Initial Value | Description | Sec. | |
| +----------------------+---------+---------------+---------------+-------------------------+-------+ |
| | BLEND_EQUATION_RGB | 8* x Z7 | GetIntegeri_v | FUNC_ADD | RGB Blending Equation | 4.1.7 | |
| | | | | | for Draw Buffer i | | |
| +----------------------+---------+---------------+---------------+-------------------------+-------+ |
| | BLEND_EQUATION_ALPHA | 8* x Z7 | GetIntegeri_v | FUNC_ADD | Alpha Blending Equation | 4.1.7 | |
| | | | | | for Draw Buffer i | | |
| +----------------------+---------+---------------+---------------+-------------------------+-------+ |
| |
| * Note that the only change change is that BLEND_EQUATION_RGB and |
| BLEND_EQUATION_ALPHA are now Z7 rather than Z5. |
| |
| Issues |
| |
| 1) Why not just implement AMD_blend_factor_minmax? |
| |
| RESOLVED: NVIDIA has a precision limitation and orthogonality |
| restrictions. |
| |
| Rather than pollute the AMD extension with an incomplete |
| implementation, this comparable NV version is API-consistent |
| (uses the same token values) and same blending math but documents |
| its precision limitation and restrictions. |
| |
| 2) What is the precision limitation? |
| |
| The GL_FACTOR_MIN_AMD and GL_FACTOR_MAX_AMD blend functions are |
| allowed to compute their blend results in half-precision even |
| when the framebuffer format is single-precision. In practice, |
| this means the blend modes work but will quantize results |
| to the representable range of half-precision, even if the |
| framebuffer is full precision. |
| |
| This limitation matches the allowance of the advanced blend |
| equations introduced by NV_blend_equation_advanced (and |
| standardized by KHR_blend_equation and OpenGL 4.5 and ES 3.2). |
| |
| This means magnitudes beyond the largest representable magnitude |
| of half-precision may be mapped to infinity. Magnitudes less |
| than the smallest representable non-zero magnitude may be mapped |
| to zero. Mantissa bits may be quantied. |
| |
| While this limitation allows implementations to perform these |
| blend modes in half-precision, it does not require the blend |
| modes to be performed in half-precsion. Implementations are |
| allowed to blend with better numerics than half-precision. |
| This being said, expect NVIDIA implementations circa 2017 to |
| implement these blend modes using half-precision numerics. |
| |
| 3) What are the orthogonality restrictions? |
| |
| If more than one draw buffer is configured |
| with glDrawBuffers (or similar command) and |
| NVX_blend_equation_advanced_multi_draw_buffers is supported and at |
| least one of the non-NONE draw buffers has GL_FACTOR_MIN_AMD or |
| GL_FACTOR_MAX_AMD configured as the buffer's RGB or alpha blend |
| equation, then all non-NONE draw buffers must have identical |
| blend equations configuration for RGB and alpha; otherwise the |
| error GL_INVALID_OPERATION is generated. |
| |
| If more than one draw buffer is configured |
| with glDrawBuffers (or similar command) and |
| NVX_blend_equation_advanced_multi_draw_buffers is NOT |
| supported and any one or more of the non-NONE draw buffers has |
| GL_FACTOR_MIN_AMD or GL_FACTOR_MAX_AMD configured as the buffer's |
| blend equation, the error GL_INVALID_OPERATION is generated. |
| |
| If any source or destination blend factor is one of GL_SRC1_COLOR |
| for that draw buffer, GL_SRC1_ALPHA, GL_ONE_MINUS_SRC1_COLOR, |
| or GL_ONE_MINUS_SRC1_ALPHA (the dual-source blending factors |
| introduced by ARB_blend_func_extended and EXT_blend_func_extended |
| and standardized by OpenGL 3.3) for a given enabled draw buffer, |
| the error GL_INVALID_OPERATION is generated. |
| |
| 4) Do the blend parameters GL_BLEND_PREMULTIPLIED_SRC_NV and |
| GL_BLEND_OVERLAP_NV apply to GL_FACTOR_MIN_AMD and GL_FACTOR_MAX_AMD. |
| |
| RESOLVED: No. |
| |
| These blend parameters are intended to affect advanced blend modes |
| expressed as RGBA compositing operators. GL_FACTOR_MIN_ARM and |
| GL_FACTOR_MAX_AMD can be used separately for RGB and alpha so these |
| blend parameters should not apply to them. |
| |
| 5) Will these blend modes be coherent |
| if NV_blend_equation_advanced_coherent or |
| KHR_blend_equation_advanced_coherent are not supported? |
| |
| RESOLVED: No, but they should still operate if |
| NV_blend_minmax_factor is advertised. glBlendBarrierNV or |
| glBlendBarrierKHR will be needed to ensure coherency for |
| overlapping primitives. |
| |
| 6) What NVIDIA GPUs can be expected to implement this extension? |
| |
| RESOLVED: The same set that advertise |
| KHR_blend_equation_advanced_coherent and |
| NV_blend_equation_advanced_coherent. |
| |
| In practice, this is Maxwell GPUs and beyond. |
| |
| 7) Does this extension support OpenGL ES? |
| |
| RESOLVED: Yes. |
| |
| Revision History |
| |
| Rev. Date Author Changes |
| ---- -------- -------- ----------------------------------------- |
| 3 07/26/2017 mjk public release |
