| Name |
| |
| EXT_shader_texture_lod |
| |
| Name Strings |
| |
| GL_EXT_shader_texture_lod |
| |
| Contributors |
| |
| Benj Lipchak |
| Ben Bowman |
| |
| and contributors to the ARB_shader_texture_lod spec, |
| which provided the basis for this spec. |
| |
| Contact |
| |
| Benj Lipchak, Apple (lipchak 'at' apple.com) |
| |
| IP Status |
| |
| No known IP issues. |
| |
| Status |
| |
| Draft |
| |
| Version |
| |
| Last Modified Date: February 24, 2011 |
| Revision: 3 |
| |
| Number |
| |
| OpenGL ES Extension #77 |
| |
| Dependencies |
| |
| This extension is written against the OpenGL ES 2.0 Specification. |
| |
| This extension is written against The OpenGL ES Shading Language, |
| Language Version 1.00, Document Revision 17. |
| |
| This extension interacts with EXT_texture_filter_anisotropic. |
| |
| Overview |
| |
| This extension adds additional texture functions to the |
| OpenGL ES Shading Language which provide the shader writer |
| with explicit control of LOD. |
| |
| Mipmap texture fetches and anisotropic texture fetches |
| require implicit derivatives to calculate rho, lambda |
| and/or the line of anisotropy. These implicit derivatives |
| will be undefined for texture fetches occurring inside |
| non-uniform control flow or for vertex shader texture |
| fetches, resulting in undefined texels. |
| |
| The additional texture functions introduced with |
| this extension provide explicit control of LOD |
| (isotropic texture functions) or provide explicit |
| derivatives (anisotropic texture functions). |
| |
| Anisotropic texture functions return defined texels |
| for mipmap texture fetches or anisotropic texture fetches, |
| even inside non-uniform control flow. Isotropic texture |
| functions return defined texels for mipmap texture fetches, |
| even inside non-uniform control flow. However, isotropic |
| texture functions return undefined texels for anisotropic |
| texture fetches. |
| |
| The existing isotropic vertex texture functions: |
| |
| vec4 texture2DLodEXT(sampler2D sampler, |
| vec2 coord, |
| float lod); |
| vec4 texture2DProjLodEXT(sampler2D sampler, |
| vec3 coord, |
| float lod); |
| vec4 texture2DProjLodEXT(sampler2D sampler, |
| vec4 coord, |
| float lod); |
| |
| vec4 textureCubeLodEXT(samplerCube sampler, |
| vec3 coord, |
| float lod); |
| |
| are added to the built-in functions for fragment shaders |
| with "EXT" suffix appended. |
| |
| New anisotropic texture functions, providing explicit |
| derivatives: |
| |
| vec4 texture2DGradEXT(sampler2D sampler, |
| vec2 P, |
| vec2 dPdx, |
| vec2 dPdy); |
| vec4 texture2DProjGradEXT(sampler2D sampler, |
| vec3 P, |
| vec2 dPdx, |
| vec2 dPdy); |
| vec4 texture2DProjGradEXT(sampler2D sampler, |
| vec4 P, |
| vec2 dPdx, |
| vec2 dPdy); |
| |
| vec4 textureCubeGradEXT(samplerCube sampler, |
| vec3 P, |
| vec3 dPdx, |
| vec3 dPdy); |
| |
| are added to the built-in functions for vertex shaders |
| and fragment shaders. |
| |
| New Procedures and Functions |
| |
| None |
| |
| New Tokens |
| |
| None |
| |
| Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL Operation) |
| |
| None |
| |
| Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization) |
| |
| In Section 3.7.7, replace the final paragraph on p. 76 with: |
| |
| "Let s(x, y) be the function that associates an s texture coordinate |
| with each set of window coordinates (x, y) that lie within a |
| primitive; define t(x, y) analogously. Let u(x, y) = wt * s(x, y) and |
| v(x, y) = ht * t(x, y), where wt and ht are equal to the width and height |
| of the level zero array. |
| |
| Let |
| dUdx = wt*dSdx; dUdy = wt*dSdy; |
| dVdx = ht*dTdx; dVdy = ht*dTdy; (3.12a) |
| |
| where dSdx indicates the derivative of s with respect to window x, |
| and similarly for dTdx. |
| |
| For a polygon, rho is given at a fragment with window coordinates |
| (x, y) by |
| |
| rho = max ( |
| sqrt(dUdx*dUdx + dVdx*dVdx), |
| sqrt(dUdy*dUdy + dVdy*dVdy) |
| ); (3.12b)" |
| |
| Additions to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment Operations and the Frame Buffer) |
| |
| None |
| |
| Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special Functions) |
| |
| None |
| |
| Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and State |
| Requests) |
| |
| None |
| |
| Additions to Appendix A of the OpenGL ES 2.0 Specification (Invariance) |
| |
| None |
| |
| Additions to version 1.00.17 of the OpenGL ES Shading Language Specification |
| |
| "A new preprocessor #define is added to the OpenGL Shading Language: |
| |
| #define GL_EXT_shader_texture_lod 1 |
| |
| Including the following line in a shader can be used to control the |
| language features described in this extension: |
| |
| #extension GL_EXT_shader_texture_lod : <behavior> |
| |
| Where <behavior> is as specified in section 3.3." |
| |
| |
| Additions to Chapter 8 of version 1.00.17 of the OpenGL ES Shading Language |
| Specification |
| |
| |
| 8.7 Texture Lookup Functions |
| |
| Delete the last paragraph, and replace with: |
| |
| "For the "Lod" functions, lod specifies lambda_base (see equation 3.11 in |
| The OpenGL ES 2.0 Specification) and specifies dSdx, dTdx = 0 and |
| dSdy, dTdy = 0 (see equation 3.12a in The OpenGL ES 2.0 Specification). |
| The "Lod" functions are allowed in a vertex shader. If enabled by the |
| preprocessor directive #extension, the "Lod" functions are also allowed in |
| a fragment shader. |
| |
| For the "Grad" functions, dPdx is the explicit derivative of P with respect |
| to window x, and similarly dPdy with respect to window y. For the "ProjGrad" |
| functions, dPdx is the explicit derivative of the projected P with respect |
| to window x, and similarly for dPdy with respect to window y. For a two- |
| dimensional texture, dPdx and dPdy are vec2. For a cube map texture, |
| dPdx and dPdy are vec3. |
| |
| Let |
| |
| dSdx = dPdx.s; |
| dSdy = dPdy.s; |
| dTdx = dPdx.t; |
| dTdy = dPdy.t; |
| |
| and |
| |
| / 0.0; for two-dimensional texture |
| dRdx = ( |
| \ dPdx.p; for cube map texture |
| |
| / 0.0; for two-dimensional texture |
| dRdy = ( |
| \ dPdy.p; for cube map texture |
| |
| (See equation 3.12a in The OpenGL ES 2.0 Specification.) |
| |
| If enabled by the preprocessor directive #extension, the "Grad" functions |
| are allowed in vertex and fragment shaders. |
| |
| All other texture functions may require implicit derivatives. Implicit |
| derivatives are undefined within non-uniform control flow or for vertex |
| shader texture fetches." |
| |
| Add the following entries to the texture function table: |
| |
| vec4 texture2DGradEXT(sampler2D sampler, |
| vec2 P, |
| vec2 dPdx, |
| vec2 dPdy); |
| vec4 texture2DProjGradEXT(sampler2D sampler, |
| vec3 P, |
| vec2 dPdx, |
| vec2 dPdy); |
| vec4 texture2DProjGradEXT(sampler2D sampler, |
| vec4 P, |
| vec2 dPdx, |
| vec2 dPdy); |
| |
| vec4 textureCubeGradEXT(samplerCube sampler, |
| vec3 P, |
| vec3 dPdx, |
| vec3 dPdy); |
| |
| Interactions with EXT_texture_anisotropic |
| |
| The Lod functions set the derivatives ds/dx, dt/dx, dr/dx, |
| dx/dy, dt/dy, and dr/dy = 0. Therefore Rhox and Rhoy = 0 |
| 0, Rhomax and Rhomin = 0. |
| |
| Revision History: |
| |
| 3 - 2011-02-24 |
| * Assign extension number |
| |
| 2 - 2010-01-20 |
| * Naming updates |
| |
| 1 - 2010-01-19 |
| * Initial ES version |
