skia / external / github.com / KhronosGroup / OpenGL-Registry / bc93187978b46e0baae0b8556071d6b292b0bb97 / . / extensions / SGIX / SGIX_cube_map.txt

XXX incomplete (but getting close) | |

Name | |

SGIX_cube_map | |

Name Strings | |

GL_SGIX_cube_map | |

Version | |

$Date: 1998/05/12 23:51:59 $ $Revision: 1.17 $ | |

Number | |

130 | |

Dependencies | |

OpenGL 1.1 is required. | |

EXT_light_texture affects the definition of this extension. | |

The enums EYE_SPACE_SGIX and OBJECT_SPACE_SGIX | |

are defined in the fragment_light_space spec and | |

used here. We aren't dependent upon the spec per-se, | |

but we do want those enums. If we had this spec without | |

fragment_light_space but with fragment_lighing, we'd | |

want to define them as part of this spec. | |

Overview | |

This extension introduces a cube map method for performing | |

environment mapping and environment map term to the fragment | |

light equation. | |

Issues | |

* What is the best way to enable environment mapping in the fragment | |

lighting equation? | |

I chose to use | |

ApplyTextureEXT(ENV_MAP_SGIX); | |

Enable(CUBE_MAP_SGIX); | |

* can cube map environment mapping be used with per-vertex lighting? | |

Sure, but it is simply a texture in this case, it is not multiplied | |

by the specular material. | |

If SGIX_texture_add_env is supported, the cube map environment | |

term can be added to the color computed in per-vertex lighting. | |

Use | |

Enable(CUBE_MAP_SGIX); | |

TexEnvi(TEXTURE_ENV,TEXTURE_ENV_MODE,ADD); | |

* do we want a way to transform the Reflection vectors by a matrix somehow? | |

Or perhaps we generate the R vector relative to the viewer. | |

The idea is if we are simulating thin film reflections or something like | |

that we want to use the environment map as a lighting map. | |

This is handled easily but clumsily with a call to | |

TexParameteri(CUBE_MAP_SGIX, ENV_MAP_SGIX, EYE_SPACE_SGIX) or | |

TexParameteri(CUBE_MAP_SGIX, ENV_MAP_SGIX, OBJECT_SPACE_SGIX) | |

the first case fixes the environment to the viewers head (needed by thin | |

film or lights fixed with the viewer), the second fixes it in the world | |

(classic environment mapping). | |

An alternative is to introduce a fragment_environment spec and | |

perhaps a call like | |

EnvironmentMapSpace({ EYE_SPACE_SGIX | | |

OBJECT_SPACE_SGIX }) | |

This spec could also add the notion of multiplying the | |

reflected environment value by the specular material to the | |

equation in the fragment lighting spec. | |

* Do we explicitly include the environment map term in fragment lighting | |

equation or use this extension (or maybe texture or light environment) instead. | |

This extension adds an environment mapping term to the fragment lighting equation | |

If we made a seperate fragment_environment spec we could add the term | |

in that spec. | |

* We need to deal with PROXY stuff to determine if all the cube map | |

faces will fit. | |

* if it says somewhere in the GL specification that whenever 1D and 2D | |

textures are enabled (I know it says this in the man page, but I can't | |

find it in the spec), 2D wins, we need the same type of language here. | |

2D wins over cubemapping if both are enabled and there is only one | |

texture resource. | |

* If we say that reflection vectors are calculated on a per-fragment basis | |

this means that bumpy reflections should be possible since N could come | |

from a texture. If we further say that the approximation of interpolating | |

an per-vertex-calculated R vector is acceptable, this causes a conflict | |

because that effect would kill bumpy reflections. | |

New Procedures and Functions | |

New Tokens | |

Accepted by the <mode> parameter of ApplyTextureEXT, and | |

the <pname> parameter of | |

TexParameterf, TexParameterfv, Texparameteri, and TexParameteriv, | |

GetTexParameterfv, GetTexParameteriv: | |

ENV_MAP_SGIX 0x8340 | |

Accepted by the <cap> parameter of Enable, Disable and IsEnabled, | |

the <target> parameter of | |

TexParameterf, TexParameterfv, Texparameteri, and TexParameteriv, | |

GetTexParameterfv, GetTexParameteriv, | |

BindTextureEXT, | |

accepted by the <pname> parameters of GetBooleanv, GetIntegerv: | |

CUBE_MAP_SGIX 0x8341 | |

Accepted by the <target> parameters of GetTexImage, | |

GetTexLevelParameterfv, GetTexLevelParameteriv, | |

TexImage2D, TexSubImage2D, CopyTexImage2D, and CopyTexSubImage2D: | |

CUBE_MAP_ZP_SGIX 0x8342 | |

CUBE_MAP_ZN_SGIX 0x8343 | |

CUBE_MAP_XN_SGIX 0x8344 | |

CUBE_MAP_XP_SGIX 0x8345 | |

CUBE_MAP_YN_SGIX 0x8346 | |

CUBE_MAP_YP_SGIX 0x8347 | |

Accepted by the <pname> parameters of GetBooleanv, GetIntegerv, | |

GetFloatv, and GetDoublev: | |

CUBE_MAP_BINDING_SGIX 0x8348 | |

Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation) | |

Additions to Chapter 3 of the 1.1 Specification (Rasterization) | |

In section 3.8 we should add text that specifies that each of | |

the 6 faces of the cube map should be legal textures | |

based on the filtering mode before cube mapping can be enabled | |

If they are not it is as if texturing is disabled. | |

Before Section 3.8.1 Texture Minification insert a new section 3.8.1 | |

Environment Map Address Calculation. | |

Environment map address calculation may be used to compute texture coordinates | |

in an environment map texture. | |

The Reflection vector 'r' is computed on | |

a per-fragment basis from interpolated view vector(VPe) and | |

interpolated normal 'n' vectors as | |

r = (X,Y,Z) = 2*n*dot(n,VPe) - VPe | |

If TexParameter is called with <pname> ENV_MAP_SGIX and | |

<param> OBJECT_SPACE_SGIX, the view vector 'VPe' is transformed | |

by the inverse of the modelview matrix before 'r' is calculated. | |

This is the default behavior. If TexParameter is called with | |

<pname> ENV_MAP_SGIX and <param> EYE_SPACE_SGIX, the view vector is | |

unchanged before the calculation of the reflection vector. | |

The calculation of 'r' may be approximated by computing it on a | |

per-vertex basis, transforming by the inverse of the modelview matrix | |

if necessary, optionally normalizing it for numerical purposes | |

and then interpolating it on a per-pixel basis. | |

This will lead to unacceptable distortion effects if r varies greatly on a | |

per-vertex basis and will also prevent the use of reflection vector generation | |

from a texture derived normal since the calculation of R occurs before | |

the texture stage. | |

Cube Map Face Selection | |

If the environment map is implemented with a cube map, one of the six faces of | |

the cube is selected by the major axis of the reflection vector on a per-pixel | |

basis. | |

major axis X Y Z | |

----------------------------------------------------------- | |

<= 0 CUBE_MAP_XN_SGIX CUBE_MAP_YN_SGIX CUBE_MAP_ZN_SGIX | |

> 0 CUBE_MAP_XP_SGIX CUBE_MAP_YP_SGIX CUBE_MAP_ZN_SGIX | |

Once the face is selected, the s,t texture coordinates are computed | |

from the (X,Y,Z) coordinates of the reflection vector and replace | |

any texture coordinates specified with TexCoord or generated by TexGen as: | |

map s t r q | |

------------------------------------------------------------- | |

CUBE_MAP_ZN_SGIX .5 - .5*X/Z .5 - .5*Y/Z 0. 1. | |

CUBE_MAP_ZP_SGIX .5 - .5*X/Z .5 + .5*Y/Z 0. 1. | |

CUBE_MAP_XN_SGIX .5 + .5*Z/X .5 - .5*Y/X 0. 1. | |

CUBE_MAP_XP_SGIX .5 + .5*Z/X .5 + .5*Y/X 0. 1. | |

CUBE_MAP_YN_SGIX .5 - .5*X/Y .5 + .5*Z/Y 0. 1. | |

CUBE_MAP_YP_SGIX .5 + .5*X/Y .5 + .5*Z/Y 0. 1. | |

note to spec editor: (see the figure in file cubemap.sho to visualize the mappings.) | |

Level of detail should be computed in a manner that corresponds to | |

the specification of level of detail for two-dimensional texturing. | |

Note that the chain rule can be applied using the above formulas and | |

slope information for X,Y,Z (dX/dx, dY/dx, dZ/dx, dX/dy, dY/dy, dZ/dy) | |

to obtain ds/dx, ds/dy, dt/dx, dt/dy. | |

e.g. ds/dx = dX/dx*ds/dX + dY/dx*ds/dY + dZ/dx*ds/dZ | |

We add an enviroment map term to the equation in section 3.9.2 from the | |

fragment_lighting spec: | |

The desired general equation for the fragment illumination model is: | |

Cl = Em emissive | |

+ Am*As ambient material*scene ambient color | |

SUM{_i = 0 through Nf-1} { | |

+ Atten_i*SpotL_i*{ distance/spot light attenuation | |

+ Am*Al_i ambient material*ambient light | |

+ Dm*Dl_i*(N.L_i) diffuse material*diffuse light | |

+ Sm*Sl_i*(N.H_i)^n specular material*specular light | |

} | |

} | |

+Sm*Ev | |

Nf is the number of fragment light sources | |

N is the fragment normal vector | |

L_i is the direction vector from the fragment position to the light source | |

H_i is the half angle vector | |

n is the specular exponent (shininess) | |

Ev is the environment map value. | |

Ev is defined to be 0 unless | |

ApplyTextureEXT(ENV_MAP_SGIX) has been called in conjunction | |

with an enabled texture in which case the value is | |

the value determined from the cube map access as specified above. | |

Additions to Chapter 4 of the 1.1 Specification (Per-Fragment Operations | |

and the Framebuffer) | |

None | |

Additions to Chapter 5 of the 1.1 Specification (Special Functions) | |

None | |

Additions to Chapter 6 of the 1.1 Specification (State and State Requests) | |

Although many of the parameter values of a set of cube map textures have no | |

effect on texture operation, they are maintained and may be queried. | |

There is no value associated with the binding points | |

CUBE_MAP_ZP_2D_SGIX, | |

CUBE_MAP_ZN_2D_SGIX, | |

CUBE_MAP_XN_2D_SGIX, | |

CUBE_MAP_XP_2D_SGIX, | |

CUBE_MAP_YN_2D_SGIX, | |

CUBE_MAP_YP_2D_SGIX, | |

so they are not accepted as the <pname> parameter | |

of GetBooleanv, GetIntegerv, GetFloatv, or GetDoublev. The name of | |

the set of cube map textures that are bound to the above binding posts are queried | |

by calling GetBooleanv, GetIntegerv, GetFloatv, or GetDoublev with | |

<pname> set to CUBE_MAP_BINDING_SGIX. | |

Zero is returned if no texture has been bound. | |

Additions to the GLX Specification | |

None | |

Dependencies on EXT_light_texture | |

If EXT_light_texture is not supported, then references to | |

ApplyTextureEXT() are to be ignored. | |

Errors | |

INVALID_VALUE is generated if BindTextureEXT parameter <target> is | |

one of CUBE_MAP_SGIX | |

and parameter <texture> is not the name of a | |

cube map texture, the name of an as yet unbound texture, or zero. | |

* more of these * | |

New State | |

Get Value Get Command Type Initial Value Attribute | |

--------- ----------- ---- ------------- --------- | |

CUBE_MAP_BINDING_SGIX GetIntegerv Z+ 0 texture | |

ENV_MAP_SGIX GetTexParameteriv Z2 OBJECT_SPACE_SGIX texture | |

CUBE_MAP IsEnabled XXX? | |

CUBE_MAP_ZP_2D_SGIX etc XXX (how do we specify this?) | |

New Implementation Dependent State | |

None |