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

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Name | |

SGIX_nonlinear_lighting_pervertex | |

Name Strings | |

GL_SGIX_nonlinear_lighting_pervertex | |

Version | |

$Date: 1997/09/23 23:20:38 $ $Revision: 1.1 $ | |

Number | |

??? | |

Dependencies | |

OpenGL 1.1 is required. | |

Overview | |

This extension adds new functionality to the per-vertex lighting | |

model of OpenGL. It facilitates a nonlinear approximation of | |

reflectance functions of materials. This extension is based upon | |

research conducted at Cornell University and detailed in the | |

SIGGRAPH 97 proceedings (LaFortune, pp. 117-126). When active, | |

this reflectance model replaces diffuse and specular (and ambient?) | |

reflection with a single, generalized material description. | |

The fundamental equation for nonlinear reflectance can be expressed | |

as the following weighte dot-product: | |

Fr(u,v) = Ps*(Cx*ux*vx + Cy*uy*vy + Cz*uz*vz)^n | |

Where: u = light vector at a vertex | |

v = eye vector at a vertex | |

Ps = maximum albedo (fully-illuminated material color) | |

C = nonlinear scaling coefficients | |

n = specular exponent (~shininess) | |

The magnitude of the C vector equals (n+2)/2pi and represents the | |

normalization constant. | |

A given material will be influenced by a number Ps, C coeffients | |

(analagous to specular, diffuse, ambient components in the basic | |

OpenGL lighting model). As in the OpenGL 1.1 lighting model, the | |

final color for a point is expressed as a sum of equations of the | |

same format as Fr: | |

Fr(u,v) = Sum(i,N)(Cx,i*ux*vx + Cy,i*uy*vy + Cz,i*uz*vz)^ni | |

Where the reflectance at a point is defined by the sum of N | |

expressions. Each dot product is characterized by the following | |

coefficients: | |

Ci = coefficient vectors with with color absorbed | |

ni = specular exponents | |

In the context of OpenGL, it makes sense to make the magnitude of | |

Ci be (ni+2)/2pi and keep the color (RGBA) vector separate. | |

This extension will be implemented in the OpenGL pipeline directly | |

in place of the per-vertex specular, diffuse lighting. | |

Issues | |

* Should ambient lighting calculations remain active when nonlinear | |

reflectance is enabled? | |

* Should we only allow a single Alpha component to be used, as in | |

the OpenGL 1.1 model? | |

* Because of the potentially large amount of data associated (relative | |

to OpenGL 1.1 materials) with a material, should a "Material Object" | |

extension be considered? | |

* Should Nonlinear Lighting be allowed in Color_Index mode? | |

* Should the vertex colors be clamped positive? This will inhibit multipassing... | |

* Are there any dependencies on other extensions? | |

New Procedures and Functions | |

Because of the potentially large number of nonlinear terms, special | |

"Nonlin" versions of Material, Light have been added in this extension. | |

These functions affect lighting state in a manner identical to Material | |

and Light, with a different calling convention. | |

void NonlinMaterialfvSGIX(enum face, enum pname, int terms, const float *params); | |

void GetNonlinMaterialfvSGIX(enum face, enum pname, int *terms, const float *data); | |

void NonlinLightfvSGIX(enum light, enum pname, int terms, float *params); | |

void GetNonlinLightfvSGIX(enum light, enum pname, int *terms, float *data); | |

New Tokens | |

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

the <pname> parameters of GetBooleanv, GetIntegerv, GetFloatv, and | |

GetDoublev: | |

NONLIN_LIGHTING_SGIX 0x???? | |

Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, | |

and GetDoublev: | |

MAX_NONLIN_TERMS_SGIX 0x???? | |

MAX_NONLIN_LIGHTS_SGIX 0x????+1 | |

Accepted by the <pname> parameter of NonlinMaterialv, NonlinLightv: | |

COLOR_SGIX 0x???? | |

Accepted by the <pname> parameter of NonlinMaterialv: | |

WEIGHT_SGIX 0x???? | |

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

Section 2.13.1 Lighting | |

... <paragraph 2> | |

Lighting may be in one of three states: | |

... | |

2. Lighting On, Nonlinear Reflectance Disabled. In this state, | |

a vertex's color is found by computing a value given the | |

current lighting parameters and using the specular/diffuse | |

reflectance model. | |

3. Lighting On, Nonlinear Reflectance Enabled. In this state, | |

a vertex's color is found by computing a value given the | |

current lighting parameters and using the nonlinear reflectance | |

model. | |

Lighting is turned either on or off using the generic Enable or | |

Disable commands with the symbolic value LIGHTING. Nonlinear | |

Reflectance is turned either on or off using the generic Enable or | |

Disable commands with the symbolic value NONLIN_LIGHTING_SGIX. | |

Nonlinear Reflectance has no effect if lighting is off. | |

...<paragraph 3 - Lighting Operation> | |

A lighting parameter is one of seven types: color, position, direction, | |

weight, real, int, or boolean. | |

... | |

A weight parameter consists of 3 floating-point elements, one for | |

each of Cx, Cy, and Cz, in that order. There are no restrictions on | |

the allowable values for the weight parameter. | |

... | |

An int parameter is one integer value. | |

...<table 2.7> | |

Nonlinear Material Parameters | |

wcm,j weight (0.0,0.0,0.0) jth reflectance weight of material | |

srm,j real 1.0 jth specular exponent of material | |

ccm,j color (0.8,0.8,0.8,1.0) jth color of material | |

tnlm int 0 Maximum (j+1) of material | |

... | |

Nonlinear Light Source Parameters | |

ncli,j(i=0) color (1.0,1.0,1.0,1.0) jth intensity of light 0 | |

ncli,j(i>0) color (0.0,0.0,0.0,1.0) jth intensity of light i | |

tnll int 0 Maximum (j+1) light | |

...<Page 45> | |

If nonlinear reflectance is disabled, the color c produced... | |

...If nonlinear reflectance is enabled, the color c produced by lighting a | |

vertex is given by | |

c = ecm + acm*acs + | |

sum<i=0,n-1>(sum<j=0,min(tnlm, tnll)-1>(acm*acli + | |

(fi)(nx*hx*wcmx,j + ny*hy*wcmy,j + nz*hz*wcmzj)^srm,j * | |

ccm,j*ncli,j)) | |

Section 2.13.2 Lighting Parameter Specification | |

... <paragraph 1.5> | |

...Material... | |

void NonlinMaterial{f}v( enum face, enum pname, int terms, T params ) ; | |

...Light... | |

void NonlinLight{f}v( enum light, enum pname, int terms, T params ) ; | |

... <paragraph 2> | |

... params is a pointer... terms is an integer indicating how many terms | |

of a nonlinear lighting equation are being specified by a function call. | |

...For the Material or NonlinMaterial commands, face must be one of... | |

... <table 2.8> | |

Nonlinear Material Parameters(NonlinMaterial) | |

wcm,j WEIGHT 3*terms | |

ccm,j COLOR 4*terms | |

srm,j SHININESS terms | |

tnlm terms 1 | |

... | |

Nonlinear Light Source Parameters(NonlinLight) | |

ncli,j COLOR 4*terms | |

tnll terms 1 | |

Section 2.13.3 ColorMaterial | |

... <paragraph 1> | |

...by calling Enable or Disable with the symbolic value COLOR_MATERIAL. | |

The error INVALID_OPERATION is generated if COLOR_MATERIAL is Enabled | |

while NONLIN_LIGHTING is enabled. | |

Section 2.14.4 Lighting State | |

... <paragraph 1> | |

...The state required...a bit indicating whether or not NONLINEAR_LIGHTING | |

is enabled, and a single... | |

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

None | |

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

and the Frame Buffer) | |

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) | |

... <page 145, list of functions> | |

void GetNonlinLight{f}v( enum light, enum value, int *terms, T *data ) ; | |

void GetNonlinMaterial{f}v( enum face, enum value, int *terms, T *data ) ; | |

... <page 145, new paragraph between GetMaterial and GetTexParameter> | |

GetNonlinLight and GetNonlinMaterial are similar to their GetLight | |

and GetMaterial counterparts, except that they return by reference | |

the number of terms (int *terms) and an array of parameters (T *data). | |

The *data pointer passed to GetNonlinMaterial and GetNonlinLight should | |

point to an array large enough to contain MAX_NONLIN_TERMS*components, | |

where components equals the number of floats comprising a datum. | |

... <table 6.3> | |

W Weight (floating-point Cx, Cy, Cz values) | |

Additions to the GLX Specification | |

TBD | |

Dependencies on SGI_extension_name | |

None? | |

Errors | |

INVALID_OPERATION is generated if the user attempts to enable both | |

COLOR_MATERIAL and NONLINEAR_LIGHTING, irregardless of order. | |

INVALID_ENUM is generated if NonlinLight{f}vSGIX parameter <pname> is not | |

COLOR or <light> is not valid (LIGHT{0..MAX_NONLIN_LIGHTS-1}. | |

INVALID_VALUE is generated if NonlinLight{f}vSGIX parameter <terms> is | |

outside the range [0..MAX_NONLIN_TERMS). | |

INVALID_OPERATION is generated if the number of terms for an active | |

light differs from the current material, or if the number of terms | |

for SHININESS, WEIGHTS and COLOR differ. This error results from | |

primitive specification. | |

INVALID_ENUM is generated if NonlinMaterial{T}vSGIX parameter <face> is | |

not FRONT, BACK, or FRONT_AND_BACK. | |

INVALID_ENUM is generated if NonlinMaterial{T}vSGIX parameter <pname> is | |

not COLOR, SHININESS, or WEIGHT. | |

INVALID_VALUE is generated if NonlinMaterial{T}vSGIX parameter <terms> is | |

outside the range [0..MAX_NONLIN_TERMS). | |

INVALID_ENUM is generated if GetNonlinLight{t}vSGIX parameter <light> | |

is not valid (LIGHT{0..MAX_NONLIN_LIGHTS-1}. | |

INVALID_ENUM is generated if GetNonlinLight{t}vSGIX parameter <pname> | |

is not COLOR. | |

INVALID_ENUM is generated if GetNonlinMaterial{t}vSGIX parameter <face> | |

is not FRONT, BACK, or FRONT_AND_BACK. | |

INVALID_ENUM is generated if GetNonlinMaterial{t}vSGIX parameter <pname> | |

is not COLOR, SHININESS, or WEIGHT. | |

New State | |

Initial | |

Get Value Get Command Type Value Attrib | |

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

NONLINEAR_LIGHTING_SGIX IsEnabled B False lighting/enable | |

COLOR_SGIX GetNonlinLightfvSGIX 1*xC () lighting | |

COLOR_SGIX GetNonlinMaterialfvSGIX 1*xC () lighting | |

WEIGHT_SGIX GetNonlinMaterialfvSGIX 1*xW (1.0,1.0,1.0) lighting | |

SHININESS GetNonlinMaterialfvSGIX 1*xR 1.0 lighting | |

(material color terms) GetNonlinMaterialfvSGIX Z+ 0 lighting | |

(light color terms) GetNonlinLightfvSGIX Z+ 0 lighting | |

(material weight terms) GetNonlinMaterialfvSGIX Z+ 0 lighting | |

(material shininess terms) GetNonlinMaterialfvSGIX Z+ 0 lighting | |

New Implementation Dependent State | |

Minimum | |

Get Value Get Command Type Value | |

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

MAX_NONLIN_LIGHTS_SGIX GetInteger Z+ 1 | |

MAX_NONLIN_TERMS_SGIX GetIngeger Z+ 12 |