| Name |
| |
| ARB_texture_filter_minmax |
| |
| Name Strings |
| |
| GL_ARB_texture_filter_minmax |
| |
| Contact |
| |
| Jon Leech (oddhack 'at' sonic.net) |
| Pat Brown, NVIDIA Corporation (pbrown 'at' nvidia.com) |
| |
| Contributors |
| |
| Jeff Bolz, NVIDIA Corporation |
| Mark Kilgard, NVIDIA Corporation |
| Eric Werness, NVIDIA Corporation |
| James Helferty, NVIDIA Corporation |
| Daniel Koch, NVIDIA Corporation |
| |
| Notice |
| |
| Copyright (c) 2015 The Khronos Group Inc. Copyright terms at |
| http://www.khronos.org/registry/speccopyright.html |
| |
| Specification Update Policy |
| |
| Khronos-approved extension specifications are updated in response to |
| issues and bugs prioritized by the Khronos OpenGL Working Group. For |
| extensions which have been promoted to a core Specification, fixes will |
| first appear in the latest version of that core Specification, and will |
| eventually be backported to the extension document. This policy is |
| described in more detail at |
| https://www.khronos.org/registry/OpenGL/docs/update_policy.php |
| |
| Status |
| |
| Complete. Approved by the ARB on June 26, 2015. |
| Ratified by the Khronos Board of Promoters on August 7, 2015. |
| |
| Version |
| |
| Version 6, April 20, 2015 |
| |
| Number |
| |
| ARB Extension #188 |
| |
| Dependencies |
| |
| This extension is written against the OpenGL 4.5 Specification (Core |
| Profile), dated February 2, 2015. |
| |
| OpenGL 3.3 is required. |
| |
| This extension interacts with EXT_texture_filter_anisotropic. |
| |
| Overview |
| |
| In unextended OpenGL, minification and magnification filters such as |
| LINEAR allow texture lookups to returned a filtered texel value produced |
| by computing an weighted average of a collection of texels in the |
| neighborhood of the texture coordinate provided. |
| |
| This extension provides a new texture and sampler parameter |
| (TEXTURE_REDUCTION_MODE_ARB) which allows applications to produce a |
| filtered texel value by computing a component-wise minimum (MIN) or |
| maximum (MAX) of the texels that would normally be averaged. The |
| reduction mode is orthogonal to the minification and magnification filter |
| parameters. The filter parameters are used to identify the set of texels |
| used to produce a final filtered value; the reduction mode identifies how |
| these texels are combined. |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <pname> parameter to SamplerParameter{i f}{v}, |
| SamplerParameterI{u}iv, GetSamplerParameter{i f}v, |
| GetSamplerParameterI{u}iv, TexParameter{i f}{v}, TexParameterI{u}iv, |
| GetTexParameter{i f}v, GetTexParameterI{u}iv, TextureParameter{i f}{v}, |
| TextureParameterI{u}iv, GetTextureParameter{i f}v, |
| and GetTextureParameterI{u}iv: |
| |
| TEXTURE_REDUCTION_MODE_ARB 0x9366 |
| |
| Accepted by the <param> or <params> parameter to SamplerParameter{i f}{v}, |
| SamplerParameterI{u}iv, TexParameter{i f}{v}, TexParameterI{u}iv, |
| TextureParameter{i f}{v}, and TextureParameterI{u}iv when <pname> is |
| TEXTURE_REDUCTION_MODE_ARB: |
| |
| WEIGHTED_AVERAGE_ARB 0x9367 |
| MIN (reused from core) |
| MAX (reused from core) |
| |
| Modifications to the OpenGL 4.3 Specification (Compatibility Profile) |
| |
| Modify Section 8.10, Texture Parameters |
| |
| (add to Table 8.17, pp 227-228.) |
| |
| Name Type Legal Values |
| -------------------------- ---- -------------------- |
| TEXTURE_REDUCTION_MODE_ARB enum WEIGHTED_AVERAGE_ARB, |
| MIN, MAX |
| |
| [[ jon - Note that the generalized error language for Tex*Parameter* and |
| SamplerParameter* catches the pname/param mismatch for this parameter, |
| previously mentioned explicitly in the "Errors" section of the EXT spec. |
| ]] |
| |
| |
| Modify Section 8.14.2, Coordinate Wrapping and Texel Selection |
| |
| (add below the equations specifying the values i_0, j_0, ... beta, gamma |
| on p. 246): |
| |
| ... where frac(x) denotes the fractional part of <x>, and may be |
| quantized to a fixed-point value with implementation-dependent |
| precision. |
| |
| |
| Modify Section 8.14.3, Mipmapping |
| |
| (modify the last paragraph in the section, p. 251) |
| |
| The final texture value is then found as: |
| |
| tau = (1 - frac(lambda)) * tau_1 + frac(lambda) * tau_2, |
| |
| where frac(x) denotes the fractional part of <x> and may be quantized to |
| a fixed-point value with implementation-dependent precision. |
| |
| |
| Modify Section 8.17, Texture Completeness |
| |
| [[ Jon - this change is with regard to the 20150421 GL 4.5 spec update and |
| the changes in the completeness list resulting from bug 12791 ]] |
| |
| (modify the last bullet in the section, p. 264, so that this point only |
| applies when the reduction mode samples from two mip levels): |
| |
| * Any of |
| |
| - The internal format of the texture arrays is integer (see tables |
| 8.19- 8.20), and the texture reduction mode is WEIGHTED_AVERAGE_ARB; |
| |
| - THe internal format is STENCIL_INDEX; |
| |
| - The internal format is DEPTH_STENCIL, the value of |
| DEPTH_STENCIL_TEXTURE_MODE for the texture is STENCIL_INDEX, and the |
| texture reduction mode is WEIGHTED_AVERAGE_ARB |
| |
| and either the magnification filter is not NEAREST, or the |
| minification filter is neither NEAREST nor NEAREST_MIPMAP_NEAREST. |
| |
| (add a new bullet point expressing the constraints on supported texture |
| formats) |
| |
| * The texture reduction mode is MIN or MAX, and that reduction mode is |
| not supported for the texture dimensionality, multisample state, and |
| internal format. Support for these reduction modes is only |
| guaranteed in the following cases: |
| |
| - The texture is not multisampled (see section 8.8) |
| - The internal format of the texture image is RED |
| [[ Compatibility profile only: add LUMINANCE and INTENSITY ]] |
| - The data type of the texture image is fixed- or floating-point. |
| |
| Implementations may also support these reduction modes for other |
| formats. Such support can be determined by calling |
| GetInternalformat* (see section 22.3) with <pname> |
| TEXTURE_REDUCTION_MODE_ARB. |
| |
| |
| Insert before Section 8.24, sRGB Texture Color Conversion (p. 271) |
| |
| Section 8.23post, Texture Reduction Modes |
| |
| When using minification and magnification filters such as LINEAR, or when |
| using anisotropic texture filtering, the values of multiple texels will |
| normally be combined using a weighted average to produce a filtered |
| texture value. However, a filtered texture value may also be produced by |
| computing per-component minimum and maximum values over the set of texels |
| that would normally be averaged. The texture and sampler parameter |
| TEXTURE_REDUCTION_MODE_EXT controls the process by which multiple texels |
| are combined to produce a filtered texture value. When set to its default |
| state of WEIGHTED_AVERAGE_EXT, a weighted average will be computed, as |
| described in previous sections. |
| |
| When TEXTURE_REDUCTION_MODE_ARB is MIN or MAX, the equations to produce a |
| filtered texel value for LINEAR minification or magnification filters |
| (equation 8.10 and subsequent unnumbered ones) are replaced with |
| |
| tau = reduce((1-alpha)*(1-beta)*(1-gamma), tau_i0_j0_k0, |
| ( alpha)*(1-beta)*(1-gamma), tau_i1_j0_k0, |
| (1-alpha)*( beta)*(1-gamma), tau_i0_j1_k0, |
| ( alpha)*( beta)*(1-gamma), tau_i1_j1_k0, |
| (1-alpha)*(1-beta)*( gamma), tau_i0_j0_k1, |
| ( alpha)*(1-beta)*( gamma), tau_i1_j0_k1, |
| (1-alpha)*( beta)*( gamma), tau_i0_j1_k1, |
| ( alpha)*( beta)*( gamma), tau_i1_j1_k1), |
| |
| tau = reduce((1-alpha)*(1-beta), tau_i0_j0, |
| ( alpha)*(1-beta), tau_i1_j0, |
| (1-alpha)*( beta), tau_i0_j1, |
| ( alpha)*( beta), tau_i1_j1), or |
| |
| tau = reduce((1-alpha), tau_i0, |
| ( alpha), tau_i1) |
| |
| for three-, two-, and one-dimensional texture accesses, respectively. The |
| function reduce() is defined to operate on pairs of weights and texel |
| values. If the reduction mode is MIN or MAX, reduce() computes a |
| component-wise minimum or maximum, respectively, of the R, G, B, and A |
| components of the set of provided texels with non-zero weights. |
| |
| For minification filters involving two texture levels |
| (NEAREST_MIPMAP_LINEAR and LINEAR_MIPMAP_LINEAR), filtered values for the |
| two selected levels, tau_1 and tau_2, are produced as described in section |
| 8.14.3, but using the reductions described immediately above. The two |
| filtered values will be combined to generate a final result using the |
| equation |
| |
| tau = reduce((1-frac(lambda)), tau_1, |
| ( frac(lambda)), tau_2), |
| |
| where tau_1 and tau_2 are filtered values for levels d_1 and d_2, and |
| frac(lambda) is the fractional portion of the texture level of detail and |
| may be quantized to a fixed-point value with implementation-dependent |
| precision. |
| |
| If anisotropic texture filtering is enabled, a reduction mode of |
| WEIGHTED_AVERAGE_ARB will produce a filtered texel value by computing a |
| weighted average of texel values, using an implementation-dependent set of |
| selected texels and weights. When using reduction modes of MIN or MAX, a |
| filtered texel value will be produced using the equation |
| |
| tau = reduce(tau_1, ..., tau_N) |
| |
| where tau_1 through tau_N are the <N> texels that would be used with |
| non-zero weights when a reduction mode of WEIGHTED_AVERAGE_ARB is used. |
| |
| If a texture access using a reduction mode of MIN or MAX is used with a |
| texture access with depth comparisons enabled (see section 8.23.1), the |
| individual tau values used in the reduce() functions should reflect the |
| results of the depth comparison (0.0 or 1.0), not the original values in |
| the depth texture. |
| |
| |
| Modify Section 22.3.1, Supported Operation Queries |
| |
| (add to the table of support pnames starting on p. 542) |
| |
| * TEXTURE_REDUCTION_MODE_ARB: Support for filtering with reduction modes |
| MIN and MAX is returned in <params>. |
| |
| |
| Additions to the AGL/GLX/WGL Specifications |
| |
| None. |
| |
| New State |
| |
| Add to Table 23.23, Textures (state per sampler object) |
| |
| Initial |
| Get Value Type Get Command Value Description Sec. |
| -------------------------- ---- ----------------- -------------------- ------------------------ ----- |
| TEXTURE_REDUCTION_MODE_ARB E GetTexParameteriv WEIGHTED_AVERAGE_ARB Texture reduction mode 8.10 |
| (average, minimum, maximum) |
| |
| New Implementation Dependent State |
| |
| None. |
| |
| Dependencies on EXT_texture_filter_anisotropic |
| |
| If EXT_texture_filter_anisotropic is not supported, references to |
| anisotropic filtering in the discussion of texture reduction modes should |
| be removed. |
| |
| Interactions with the compatibility profile |
| |
| If the compatibility profile is supported, then LUMINANCE and INTENSITY |
| are added to the list of formats guaranteed to support MIN and MAX |
| reduction modes. |
| |
| Issues |
| |
| (1) What should this extension be called? |
| |
| RESOLVED: ARB_texture_filter_minmax, like EXT_texture_filter_minmax on |
| which it is based. |
| |
| (2) How does this extension interact with restrictions on min/mag filters |
| textures with integer components? |
| |
| RESOLVED: In unextended OpenGL 4.3, a texture with integer components |
| (e.g., RGBA8I) is considered incomplete if used with minification or |
| magnification filters that normally average multiple samples (anything |
| other than NEAREST and NEAREST_MIPMAP_NEAREST). This restriction exists |
| to avoid the need to define semantics for computing a weighted average |
| of integer values with non-integer weights, which will produce an |
| arithmetic result that is not an integer. Given that the MIN and MAX |
| reduction modes don't do any arithmetic and won't produce non-integer |
| values, we allow these reduction modes to be used with arbitrary |
| filters. |
| |
| (3) How does this extension interact with TEXTURE_COMPARE_MODE set |
| to COMPARE_R_TO_TEXTURE for depth textures? |
| |
| RESOLVED: This extension does not require support for DEPTH_COMPONENT |
| textures with the new filter modes, but if they are supported, the |
| per-sample comparison should be performed prior to the min/max |
| reduction. |
| |
| This implies the MIN mode for TEXTURE_REDUCTION_MODE_ARB in this case |
| returns a FALSE value if *any* of the texels compare FALSE; to return |
| TRUE, every comparison must be TRUE. Likewise this implies the MAX |
| mode for TEXTURE_REDUCTION_MODE_ARB in this case returns a TRUE value |
| if *any* of the texels compare TRUE; to return FALSE, every comparison |
| must be FALSE. |
| |
| Note that unextended OpenGL 4.5 doesn't require that linear filtering |
| actually average depth comparison results of 0.0 and 1.0, but behaving |
| this way appears to be common practice and may be required for other |
| 3D graphics APIs. |
| |
| (4) Do interpolation weights figure into the min/max reductions? |
| |
| RESOLVED: Yes. Texels that would have a weight of zero for the normal |
| WEIGHTED_AVERAGE_ARB reduction modes should not be considered when |
| performing MIN or MAX reductions. |
| |
| Note that implementations may end up quantize the interpolation |
| weights to fixed-point values with implementation-dependent precision. |
| This may cause samples to be ignored in WEIGHTED_AVERAGE_ARB or |
| MIN/MAX reductions. For example, if you are using a minification |
| filter of LINEAR_MIPMAP_LINEAR and the computed LOD is 2.00001, the |
| implementation may round the LOD as being exactly 2.0 and ignore the |
| texels in level 3 for the purposes of trilinear filtering. |
| |
| (5) Should TEXTURE_REDUCTION_MODE_ARB work with stencil textures? |
| |
| RESOLVED: Yes. |
| |
| (6) What are the constraints on supported texture targets and formats? |
| |
| RESOLVED: After conducting a voting exercise, we concluded that the |
| set of supported formats would be limited to single-channel (R/L/I), |
| fixed- or floating-point, and that the GetInternalformat query should |
| be used to expose support for additional formats. |
| |
| RESOLVED: Formats which don't support MIN/MAX reduction are treated as |
| incomplete textures when those reduction modes are set. |
| |
| RESOLVED: TexParameter* does not generate an error when setting |
| MIN/MAX reduction for unsupported texture types. This can't catch all |
| misuse even when not using separate sampler objects, so only having |
| the mismatch affect completeness seems cleaner. |
| |
| DISCUSSION: Different vendors all had different constraints. There |
| were problems with multi-channel textures, multisampled textures, |
| integer textures, and depth component and stencil index textures. |
| |
| Revision History |
| |
| Version 1, 2015/02/20 (Jon Leech) |
| - Branch from EXT_texture_filter_minmax and add issue 6 from ARB |
| discussion. |
| |
| Version 2, 2015/02/25 (Jon Leech) |
| - Rebase against GL 4.5 and change suffixes to ARB. Change minimum |
| required GL version from 1.0 to 3.3 (which is where |
| SamplerParameter* commands were introduced). Add constraints on |
| texture types guaranteed to support MIN/MAX reduction in sections |
| 8.17, and query for additional supported types in section 22.3.1. |
| Remove no longer needed Errors section. Update issue 6 with proposed |
| resolution of the format compatibility issue. |
| |
| Version 3, 2015/02/26 (Jon Leech) |
| - Remove DEPTH_COMPONENT from formats guaranteed to be supported, and |
| add LUMINANCE and INTENSITY in the compatibility profile. Clean up |
| state table entry. |
| |
| Version 4, 2015/03/20 (Jon Leech) |
| - Remove nonexistent GREEN and BLUE internal formats. Remove |
| restriction to two-dimensional images (Intel determined they do not |
| require it). Update issues 3 and 6 to track restrictions of various |
| vendor hardware. |
| |
| Version 5, 2015/04/01 (Jon Leech) |
| - Reduce required format support to single-channel (R/L/I), fixed- and |
| floating-point textures only. Remove guaranteed ALPHA format support |
| in the compatibility profile. Reflow text of Issues. |
| |
| Version 6, 2015/04/20 (Jon Leech) |
| - Modify edits to the completeness conditions in section 8.17 based on |
| changes to the GL spec in this area (Bug 12791). |
