| Name |
| |
| ARB_seamless_cube_map |
| |
| Name Strings |
| |
| GL_ARB_seamless_cube_map |
| |
| Contributors |
| |
| Bill Licea-Kane, AMD |
| Bruce Merry, ARM |
| Graham Sellers, AMD |
| Ian Romanick, Intel |
| Jeff Bolz, NVIDIA |
| Pat Brown, NVIDIA |
| Pierre Boudier, AMD |
| |
| Contact |
| |
| Graham Sellers, AMD (graham.sellers 'at' amd.com) |
| |
| Notice |
| |
| Copyright (c) 2009-2013 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 July 3, 2009. |
| |
| Version |
| |
| Last Modified Date: 07/21/2009 |
| Author revision: 4 |
| |
| Number |
| |
| ARB Extension #65 |
| |
| Dependencies |
| |
| OpenGL 1.1 is required. |
| |
| ARB_texture_cube_map is required. |
| |
| EXT_texture_filter_anisotropic affects the definition of this extension. |
| |
| This extension is written against the OpenGL 3.1 Specification. |
| |
| Overview |
| |
| When sampling from cube map textures, a three-dimensional texture |
| coordinate is used to select one of the cube map faces and generate |
| a two dimensional texture coordinate ( s t ), at which a texel is |
| sampled from the determined face of the cube map texture. Each face |
| of the texture is treated as an independent two-dimensional texture, |
| and the generated ( s t ) coordinate is subjected to the same |
| clamping and wrapping rules as for any other two dimensional texture |
| fetch. |
| |
| Although it is unlikely that the generated ( s t ) coordinate lies |
| significantly outside the determined cube map face, it is often the |
| case that the locations of the individual elements required during a |
| linear sampling do not lie within the determined face, and their |
| coordinates will therefore be modified by the selected clamping and |
| wrapping rules. This often has the effect of producing seams or |
| other discontinuities in the sampled texture. |
| |
| This extension allows implementations to take samples from adjacent |
| cube map faces, providing the ability to create seamless cube maps. |
| |
| IP Status |
| |
| None. |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <cap> parameter of Enable, Disable and IsEnabled, |
| and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv |
| and GetDoublev: |
| |
| TEXTURE_CUBE_MAP_SEAMLESS 0x884F |
| |
| |
| Additions to Chapter 3 of the 3.1 Specification (Rasterization) |
| |
| Section 3.8.7, Cube Map Texture Selection, p. 143, change the last |
| paragraph from |
| |
| "This new ( s t ) is used to find a texture value in the determined |
| face's two-dimensional texture image using the rules given in |
| sections 3.8.7 through 3.8.9." |
| |
| to: |
| |
| Seamless Cube Map Filtering |
| --------------------------- |
| |
| Seamless cube map filtering is enabled or disabled by calling Enable |
| or Disable, respectively, with the symbolic constant |
| TEXTURE_CUBE_MAP_SEAMLESS. |
| |
| When seamless cube map filtering is disabled, the new (s t) is used |
| to find a texture value in the determined face's two-dimensional |
| image using the rules given in sections 3.8.9 through 3.8.10. |
| |
| When seamless cube map filtering is enabled, the rules for texel |
| selection in sections 3.8.9 through 3.8.10 are modified so that |
| texture wrap modes are ignored. Instead, |
| |
| * If NEAREST filtering is done within a miplevel, always apply wrap |
| mode CLAMP_TO_EDGE. |
| * If LINEAR filtering is done within a miplevel, always apply wrap mode |
| CLAMP_TO_BORDER. Then, |
| o If a texture sample location would lie in the texture border in |
| either u or v, instead select the corresponding texel from the |
| appropriate neighboring face. |
| o If a texture sample location would lie in the texture border in |
| both u and v (in one of the corners of the cube), there is no |
| unique neighboring face from which to extract one texel. The |
| recommended method is to average the values of the three |
| available samples. However, implementations are free to |
| construct this fourth texel in another way, so long as, when the |
| three available samples have the same value, this texel also has |
| that value. |
| |
| The required state is one bit indicating whether seamless cube map |
| filtering is enabled or disabled. Initially, it is disabled. |
| |
| Add final paragraphs to Section 3.8.7 |
| |
| "When TEXTURE_MAX_ANISOTROPY_EXT is greater than 1.0, an |
| implementation may sample from the texture at multiple locations in |
| order to produce a filtered texel value. In this case, some of the |
| required samples may lie outside the determined cube map face. If |
| TEXTURE_CUBE_MAP_SEAMLESS is enabled, it is implementation defined |
| as to whether these samples are taken from the determined face, or |
| from the appropriate adjacent cube map face." |
| |
| Errors |
| |
| None. |
| |
| Dependencies on EXT_texture_filter_anisotropic |
| |
| If EXT_texture_filter_anisotropic is not supported, remove the |
| final paragraph added to Section 3.8.6 which references |
| TEXTURE_MAX_ANISOTROPY_EXT. |
| |
| New State |
| |
| In table 6.42, Miscellaneous, p. 279, add the following: |
| |
| Get Value Type Get Command Init Val Description Sec. Attribute |
| --------------------------- ------ -------------------- -------- -------------------------- ------ --------- |
| TEXTURE_CUBE_MAP_SEAMLESS B IsEnabled FALSE Seamless cube map filtering 3.8.6 - |
| |
| New Implementation Dependent State |
| |
| None. |
| |
| Issues |
| |
| 1) Should this be a new wrap mode, or a separate state? |
| |
| RESOLVED: It cannot be a normal wrap mode because it does not |
| apply per dimension, but rather to a texture as a whole. |
| Therefore, it is a separate state item. |
| |
| 2) What is the interaction with anisotropic filtering as described |
| in EXT_texture_filter_anisotropic? |
| |
| RESOLVED: EXT_texture_filter_anisotropic leaves the |
| implementation of anisotropic filtering implementation defined. |
| Therefore, this extension does the same. |
| |
| 3) Should this be per-texture, or a global state? |
| |
| RESOLVED: While in some cases it may be desirable to mix seamless |
| and non-seamless cube map texture sampling, it is sufficient to |
| leave this spec defining a global state and provide per-texture |
| support in another extension. |
| |
| Revision History |
| |
| Rev. Date Author Changes |
| ---- -------- -------- ----------------------------------------- |
| 4 07/21/09 Jon Leech Reformat to 80 columns and update |
| ambiguous sample location to match |
| the 3.2 spec (bug 5357). |
| |
| 3 07/20/09 Jon Leech Assign enum value and remove _ARB suffix. |
| |
| 2 07/01/09 wwlk Updated per bug 5292. |
| Re-written against the OpenGL 3.1 specification. |
| |
| 1 05/07/09 gsellers Initial draft based on |
| AMD_texture_cube_face_select |
