| Name |
| |
| EXT_texture_mirror_clamp |
| |
| Name Strings |
| |
| GL_EXT_texture_mirror_clamp |
| |
| Contributors |
| |
| Walt Donovan |
| Dan Ginsburg |
| |
| Contact |
| |
| Mark J. Kilgard, NVIDIA Corporation (mjk 'at' nvidia.com) |
| |
| Status |
| |
| Shipping as of May 2004 for GeForce6. |
| |
| Version |
| |
| Last Modified Date: 2004/05/17 |
| Version: 4 |
| |
| Number |
| |
| 298 |
| |
| Issues |
| |
| How does EXT_texture_mirror_clamp extend ATI_texture_mirror_once? |
| |
| This EXT extension provides the two wrap modes that |
| ATI_texture_mirror_once adds but also adds a third new wrap mode |
| (GL_MIRROR_CLAMP_TO_BORDER_EXT). This extension uses the same |
| enumerant values for the ATI_texture_mirror_once modes. |
| |
| Why is the GL_MIRROR_CLAMP_TO_BORDER_EXT mode more interesting than |
| the two other modes? |
| |
| Rather than clamp to 100% of the edge of the texture |
| (GL_MIRROR_CLAMP_TO_EDGE_EXT) or to 50% of the edge and border |
| color (GL_MIRROR_CLAMP), it is preferable to clamp to 100% |
| of the border color (GL_MIRROR_CLAMP_TO_BORDER_EXT). This |
| avoids "bleeding" at smaller mipmap levels. |
| |
| Consider a texture that encodes a circular fall-off pattern such |
| as for a projected spotlight. A circular pattern is bi-symmetric |
| so a "mirror clamp" wrap modes can reduce the memory footprint |
| of the texture by a fourth. Far outside the spotlight pattern, |
| you'd like to sample 100% of the border color (typically black |
| for a spotlight texture). The way to achieve this without any |
| bleeding of edge texels is with GL_MIRROR_CLAMP_TO_BORDER_EXT. |
| |
| Does this extension complete the orthogonality of the current five |
| OpenGL 1.5 wrap modes? |
| |
| Yes. There are two ways for repetition to operate (repeated |
| & mirrored) and four ways for texture coordinate clamping to |
| operate (unclamped, clamp, clamp to edge, & clamp to border). |
| The complete table of all 8 modes looks like this: |
| |
| Repeat Mirror |
| +---------------- ---------------------- |
| Unclamped | REPEAT MIRRORED_REPEAT |
| Clamp | CLAMP MIRROR_CLAMP |
| Clamp to edge | CLAMP_TO_EDGE MIRROR_CLAMP_TO_EDGE |
| Clamp to border | CLAMP_TO_BORDER MIRROR_CLAMP_TO_BORDER |
| |
| OpenGL 1.0 introduced REPEAT & CLAMP. |
| OpenGL 1.2 introduced CLAMP_TO_EDGE |
| OpenGL 1.3 introduced CLAMP_TO_BORDER |
| OpenGL 1.4 introduced MIRRORED_REPEAT |
| ATI_texture_mirror_once introduced MIRROR_CLAMP & MIRROR_CLAMP_TO_EDGE |
| EXT_texture_mirror_clamp introduces MIRROR_CLAMP_TO_BORDER |
| |
| Do these three new wrap modes work with 1D, 2D, 3D, and cube map |
| texture targets? |
| |
| RESOLUTION: Yes. |
| |
| Do these three new wrap modes work with ARB_texture_non_power_of_two |
| functionality? |
| |
| RESOLUTION: Yes. |
| |
| Do these three new wrap modes interact with NV_texture_rectangle? |
| |
| RESOLUTION: Mirroring wrap modes are not supported by |
| GL_TEXTURE_RECTANGLE_NV textures. Conventional mirroring is |
| already not supported for texture rectangles so supporting |
| clamped mirroring modes should not be supported either. |
| |
| Does the specification of MIRROR_CLAMP_EXT & MIRROR_CLAMP_TO_EDGE_EXT |
| match the ATI_texture_mirror_once specification? |
| |
| I believe yes. The ATI_texture_mirror_once specification is |
| somewhat vague what happens to texture coordinates at or very |
| near (within half a texel of) zero. The presumption is that a |
| CLAMP_TO_EDGE behavior is used. This specification is quite |
| explicit that values near zero are clamped to plus or minus |
| 1/(2*N) respectively so that the CLAMP_TO_EDGE behavior is |
| explicit. |
| |
| What should this extension be called? |
| |
| Calling the extension EXT_texture_mirror_once might cause |
| confusion since this extension has additional functionality. |
| Also, "once" never appears in the specification. |
| EXT_texture_mirror_clamp is a good name because it implies |
| support for all the clamped versions of mirroring. |
| |
| There is GL_MIRRORED_REPEAT and then GL_MIRROR_CLAMP_EXT, |
| GL_MIRROR_CLAMP_TO_EDGE_EXT, and GL_MIRROR_CLAMP_TO_BORDER_EXT. |
| Why does the first enumerant name say "MIRRORED" while the other |
| three say "MIRROR"? |
| |
| This extension follows the naming precedent set by the |
| ATI_texture_mirror_once specification. |
| |
| Moreover, MIRRORED_REPEAT uses "mirrored" to help that the |
| mirroring repeats infinitely. For the other three modes, |
| there is just one mirror that occurs and then a clamp. |
| |
| Dependencies |
| |
| Written based on the wording of the OpenGL 1.4. |
| |
| Extends ATI_texture_mirror_once by adding |
| GL_MIRROR_CLAMP_TO_BORDER_EXT. |
| |
| NV_texture_rectangle trivially affects the definition of this |
| extension. |
| |
| Overview |
| |
| EXT_texture_mirror_clamp extends the set of texture wrap modes to |
| include three modes (GL_MIRROR_CLAMP_EXT, GL_MIRROR_CLAMP_TO_EDGE_EXT, |
| GL_MIRROR_CLAMP_TO_BORDER_EXT) that effectively use a texture map |
| twice as large as the original image in which the additional half |
| of the new image is a mirror image of the original image. |
| |
| This new mode relaxes the need to generate images whose opposite |
| edges match by using the original image to generate a matching |
| "mirror image". This mode allows the texture to be mirrored only |
| once in the negative s, t, and r directions. |
| |
| New Procedure and Functions |
| |
| None |
| |
| New Tokens |
| |
| Accepted by the <param> parameter of TexParameteri and TexParameterf, |
| and by the <params> parameter of TexParameteriv and TexParameterfv, |
| when their <pname> parameter is TEXTURE_WRAP_S, TEXTURE_WRAP_T, |
| or TEXTURE_WRAP_R: |
| |
| MIRROR_CLAMP_EXT 0x8742 (same value as MIRROR_CLAMP_ATI) |
| MIRROR_CLAMP_TO_EDGE_EXT 0x8743 (same value as MIRROR_CLAMP_TO_EDGE_ATI) |
| MIRROR_CLAMP_TO_BORDER_EXT 0x8912 |
| |
| Additions to Chapter 2 of the OpenGL 1.2.1 Specification (Operation) |
| |
| None |
| |
| Additions to Chapter 3 if the OpenGL 1.2.1 Specification (Rasterization): |
| |
| - (3.8.4, page 136, as amended by the NV_texture_rectangle extension) |
| |
| Add the 3 new wrap modes to the list of wrap modes unsupported for |
| the TEXTURE_RECTANGLE_NV texture target. |
| |
| "Certain texture parameter values may not be specified for textures |
| with a target of TEXTURE_RECTANGLE_NV. The error INVALID_ENUM |
| is generated if the target is TEXTURE_RECTANGLE_NV and the |
| TEXTURE_WRAP_S, TEXTURE_WRAP_T, or TEXTURE_WRAP_R parameter is set to |
| REPEAT, MIRRORED_REPEAT_IBM, MIRROR_CLAMP_EXT, MIRROR_CLAMP_TO_EDGE_EXT, and |
| MIRROR_CLAMP_TO_BORDER_EXT. The error INVALID_ENUM is generated |
| if the target is TEXTURE_RECTANGLE_NV and the TEXTURE_MIN_FILTER is |
| set to a value other than NEAREST or LINEAR (no mipmap filtering |
| is permitted). The error INVALID_ENUM is generated if the target |
| is TEXTURE_RECTANGLE_NV and TEXTURE_BASE_LEVEL is set to any value |
| other than zero." |
| |
| - Table 3.19, page 137: Change first three entries in table: |
| |
| "TEXTURE_WRAP_S integer CLAMP, CLAMP_TO_BORDER, CLAMP_TO_EDGE, |
| MIRRORED_REPEAT, MIRROR_CLAMP_EXT, |
| MIRROR_CLAMP_TO_BORDER_EXT, |
| MIRROR_CLAMP_TO_EDGE_EXT, REPEAT |
| TEXTURE_WRAP_T integer CLAMP, CLAMP_TO_BORDER, CLAMP_TO_EDGE, |
| MIRRORED_REPEAT, MIRROR_CLAMP_EXT, |
| MIRROR_CLAMP_TO_BORDER_EXT, |
| MIRROR_CLAMP_TO_EDGE_EXT, REPEAT |
| TEXTURE_WRAP_R integer CLAMP, CLAMP_TO_BORDER, CLAMP_TO_EDGE, |
| MIRRORED_REPEAT, MIRROR_CLAMP_EXT, |
| MIRROR_CLAMP_TO_BORDER_EXT, |
| MIRROR_CLAMP_TO_EDGE_EXT, REPEAT" |
| |
| - (3.8.7, page 140) After the last paragraph of the section add: |
| |
| "Wrap Mode MIRROR_CLAMP_EXT |
| |
| Wrap mode MIRROR_CLAMP_EXT mirrors and clamps the texture coordinate, |
| where mirroring and clamping a value f computes |
| |
| mirrorClamp(f) = min(1, max(1/(2*N), abs(f))) |
| |
| where N is the size of the one-, two-, or three-dimensional texture |
| image in the direction of wrapping. |
| |
| Wrap Mode MIRROR_CLAMP_TO_EDGE_EXT |
| |
| Wrap mode MIRROR_CLAMP_TO_EDGE_EXT mirrors and clamps to edge the |
| texture coordinate, where mirroring and clamping to edge a value f |
| computes |
| |
| mirrorClampToEdge(f) = min(1-1/(2*N), max(1/(2*N), abs(f))) |
| |
| where N is the size of the one-, two-, or three-dimensional texture |
| image in the direction of wrapping. |
| |
| Wrap Mode MIRROR_CLAMP_TO_BORDER_EXT |
| |
| Wrap mode MIRROR_CLAMP_TO_BORDER_EXT mirrors and clamps to border the |
| texture coordinate, where mirroring and clamping to border a value |
| f computes |
| |
| mirrorClampToBorder(f) = min(1+1/(2*N), max(1/(2*N), abs(f))) |
| |
| where N is the size of the one-, two-, or three-dimensional texture |
| image in the direction of wrapping." |
| |
| - (3.8.8, page 142) Delete this phrase because it is out of date and |
| unnecessary given the current way section 3.8.7 is written: |
| |
| "(if the wrap mode for a coordinate is CLAMP or CLAMP_TO_EDGE)" |
| |
| Additions to Chapter 4: |
| |
| None |
| |
| Additions to Chapter 5: |
| |
| None |
| |
| Additions to Chapter 6: |
| |
| None |
| |
| Additions to the GLX Specification |
| |
| None |
| |
| Dependencies on NV_texture_rectangle |
| |
| If NV_texture_rectangle is not supported, ignore the statement that |
| the initial value for the S, T, and R wrap modes is CLAMP_TO_EDGE |
| for rectangular textures. |
| |
| Ignore the error for a texture target of TEXTURE_RECTANGLE_NV. |
| |
| GLX Protocol |
| |
| None |
| |
| Errors |
| |
| INVALID_ENUM is generated when TexParameter is called with |
| a target of TEXTURE_RECTANGLE_NV and the TEXTURE_WRAP_S, |
| TEXTURE_WRAP_T, or TEXTURE_WRAP_R parameter is set to REPEAT, |
| MIRRORED_REPEAT_IBM, MIRROR_CLAMP_EXT, MIRROR_CLAMP_TO_EDGE_EXT, |
| or MIRROR_CLAMP_TO_BORDER_EXT. |
| |
| New State |
| |
| (table 6.15, p230) amend the following entries [Z5 changed to Z8]: |
| |
| Get Value Type Get Command Initial Value Description Sec Attribute |
| -------------- ---- --------------- --------------- ------------------- ----- --------- |
| TEXTURE_WRAP_S n*Z8 GetTexParameter REPEAT except Texture wrap mode S 3.8.7 texture |
| for rectangular |
| which is |
| CLAMP_TO_EDGE |
| TEXTURE_WRAP_T n*Z8 GetTexParameter REPEAT except Texture wrap mode T 3.8.7 texture |
| for rectangular |
| which is |
| CLAMP_TO_EDGE |
| TEXTURE_WRAP_R n*Z8 GetTexParameter REPEAT except Texture wrap mode R 3.8.7 texture |
| for rectangular |
| which is |
| CLAMP_TO_EDGE |
| |
| New Implementation Dependent State |
| |
| None |
