| Name |
| |
| AMD_seamless_cubemap_per_texture |
| |
| Name Strings |
| |
| GL_AMD_seamless_cubemap_per_texture |
| |
| Contributors |
| |
| Pierre Boudier |
| Graham Sellers |
| Ahmet Oguz Akyuz |
| |
| Contact |
| |
| Graham Sellers, AMD (graham.sellers 'at' amd.com) |
| |
| Status |
| |
| In Progress. |
| |
| Version |
| |
| Last Modified Date: February 3, 2017 |
| Author revision: 7 |
| |
| Number |
| |
| 383 |
| |
| Dependencies |
| |
| OpenGL 1.1 is required. |
| |
| ARB_texture_cube_map is required. |
| |
| ARB_seamless_cube_map affects the definition of this extension. |
| |
| This extension is written against the OpenGL 1.5 Specification. |
| |
| Overview |
| |
| In unextended OpenGL, cube maps are treated as sets of six, independent |
| texture images. Once a face is selected from the set, it is treated exactly |
| as any other two-dimensional texture would be. When sampling linearly from |
| the texture, all of the individual texels that would be used to to create |
| the final, bilinear sample values are taken from the same cube face. The |
| normal, two-dimensional texture coordinate wrapping modes are honored. |
| This sometimes causes seams to appear in cube maps. |
| |
| ARB_seamless_cube_map addresses this issue by providing a mechanism whereby |
| an implementation could take each of the taps of a bilinear sample from |
| a different face, spanning face boundaries and providing seamless filtering |
| from cube map textures. However, in ARB_seamless_cube_map, this feature was |
| exposed as a global state, affecting all bound cube map textures. It was not |
| possible to mix seamless and per-face cube map sampling modes during |
| multisampling. Furthermore, if an application included cube maps that were |
| meant to be sampled seamlessly and non-seamlessly, it would have to track |
| this state and enable or disable seamless cube map sampling as needed. |
| |
| This extension addresses this issue and provides an orthogonal method for |
| allowing an implementation to provide a per-texture setting for enabling |
| seamless sampling from cube maps. |
| |
| IP Status |
| |
| None. |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <pname> parameter of TexParameterf, TexParameteri, |
| TexParameterfv, TexParameteriv, GetTexParameterfv, and GetTexParameteriv: |
| |
| TEXTURE_CUBE_MAP_SEAMLESS 0x884F (Previously defined in |
| ARB_seamless_cubemap) |
| |
| Additions to Chapter 2 of the 1.5 Specification (OpenGL Operation) |
| |
| None. |
| |
| Additions to Chapter 3 of the 1.5 Specification (Rasterization) |
| |
| Section 3.8.4, Texture Parameters, p. 144, append table 3.19 with the |
| following: |
| |
| Name Type Legal Values |
| ------------------------------ ----- -------------------- |
| TEXTURE_CUBE_MAP_SEAMLESS boolean FALSE, |
| TRUE |
| |
| Section 3.8.4, Texture Parameters, p. 143, append the last paragraph with: |
| |
| "The TEXTURE_CUBE_MAP_SEAMLESS parameter is specific to cube maps |
| and may be used to control the way that the GL handles sampling from |
| coordinates that lie outside the determined cube map face (see section |
| 3.8.6)." |
| |
| Section 3.8.6, Cube Map Texture Selection, p. 145, 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: |
| |
| "If TEXTURE_CUBE_MAP_SEAMLESS is disabled globally and the value of the |
| the texture's TEXTURE_CUBE_MAP_SEAMLESS parameter is FALSE, 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 3.8.7 through |
| 3.8.9. If TEXTURE_CUBE_MAP_SEAMLESS is emabled globally or the value |
| of the texture's TEXTURE_CUBE_MAP_SEAMLESS parameter is TRUE, seamless |
| cube map sampling is enabled, and texels are read from adjacent faces as |
| described in the ARB_seamless_cube_map extension." |
| |
| Additions to Chapter 4 of the 1.5 Specification (Per-Fragment Operations |
| and the Frame Buffer) |
| |
| None. |
| |
| Additions to Chapter 5 of the 1.5 Specification (Special Functions) |
| |
| None. |
| |
| Additions to Chapter 6 of the 1.5 Specification (State and State Requests) |
| |
| Section 6.1.3, Enumerated Queries, p. 216, modify the first paragraph |
| on page 216 to read: |
| |
| "... For GetTexParameter, value must be either TEXTURE_RESIDENT or one |
| of the symbolic values in table 3.19. The TEXTURE_CUBE_MAP_SEAMLESS |
| value may only be used when target is TEXTURE_CUBE_MAP. The lod argument |
| to GetTexLevelParameter ..." |
| |
| Additions to the GLX Specification |
| |
| None. |
| |
| Errors |
| |
| INVALID_ENUM is generated by TexParameter if <pname> is |
| TEXTURE_CUBE_MAP_SEAMLESS and <target> is not TEXTURE_CUBE_MAP. |
| |
| INVALID_ENUM is generated by TexParameter if <target> is TEXTURE_CUBE_MAP, |
| <pname> is TEXTURE_CUBE_MAP_SEAMLESS and <value> is not either TRUE |
| or FALSE. |
| |
| INVALID_ENUM is generated by GetTexParameter if <pname> is |
| TEXTURE_CUBE_MAP_SEAMLESS and <target> is not TEXTURE_CUBE_MAP. |
| |
| Dependencies on ARB_seamless_cube_map |
| |
| If ARB_seamless_cube_map is not supported, the value of the |
| TEXTURE_CUBE_MAP_SEAMLESS token is still used by this extension. |
| However, seamless cubemap filtering can only be enabled or disabled on a |
| per-texture basis as glEnable and glDisable will not accept |
| TEXTURE_CUBE_MAP_SEAMLESS. Even if ARB_seamless_cube_map is not |
| supported, the behavior of seamless cube map sampling is as described in |
| that extension. The logic to enable seamless filtering will behave as if |
| TEXTURE_CUBE_MAP_SEAMLESS were disabled (the default state). |
| |
| New State |
| |
| In table 6.16, Texture Objects, p. 242, add the following: |
| |
| Get Value Type Get Command Init Val Description Sec. Attribute |
| ------------------------- ------ -------------------- -------- -------------------------- ------ --------- |
| TEXTURE_CUBE_MAP_SEAMLESS n x B GetTexParameter[if]v FALSE Seamless cubemap sampling 3.8.6 texture |
| is enabled. |
| |
| New Implementation Dependent State |
| |
| None. |
| |
| Issues |
| |
| 1) How does this extension affect ARB_seamless_cube_map? Which takes |
| priority? Explain, in plain English, how seamless filtering gets enabled. |
| |
| RESOLVED: These two extensions are orthogonal and neither requires the |
| other to function. Seamless filtering is enabled for a cube map texture |
| either when TEXTURE_CUBE_MAP_SEAMLESS is enabled globally or when the |
| value of the individual texture's TEXTURE_CUBE_MAP_SEAMLESS parameter |
| is TRUE. The default for both extensions is to leave cube map sampling as |
| described in unextended OpenGL. Thus, an application may use either |
| extension and its behavior will be the same, regardless of the presence |
| of support for or use of the other. |
| |
| Revision History |
| |
| Rev. Date Author Changes |
| ---- -------- -------- ----------------------------------------- |
| 7 02/03/17 Jon Leech Remove ARB suffix from TEXTURE_CUBE_MAP_SEAMLESS |
| (public bug 337). |
| 6 08/18/09 gsellers Renamed from AMD_texture_cube_face_select to |
| AMD_seamless_cubemap_per_texture to better follow |
| ARB version. |
| Use ARB token, GL_TRUE and GL_FALSE rather than |
| SAME_FACE and NEXT_FACE. |
| Change type of texture parameter to boolean. |
| Change wording of resolution to issue 1 to reflect |
| the new token names. |
| 5 05/08/09 gsellers Large rewrite after splitting global and |
| per-texture support into two extensions. |
| 4 05/05/09 gsellers Change token names for consistency. Include |
| interaction with EXT_texture_filter_anisotropic. |
| 3 04/09/09 gsellers Fix 'selected' language. Suggest behavior for |
| cases where ( s, t ) lies directly at a cube map |
| corner |
| 2 04/07/09 gsellers Minor updates |
| 1 04/06/09 gsellers Initial draft |
