skia / external / github.com / KhronosGroup / OpenGL-Registry / 8acd36befc2dcb6218e6bf6e23e6e48c74463a35 / . / extensions / EXT / EXT_shader_texture_lod.txt

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 |