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GL_SGIX_fragment_specular_lighting
XXX - Dead -- couldn't convince the ARB. Use fragment_lighting &
XXX separate_specular_color instead.
XXX - Not complete yet!!!
SGIX_fragment_specular_lighting
Name Strings
GL_SGIX_fragment_specular_lighting
Version
$Date: 1998/07/06 19:51:38 $ $Revision: 1.2 $
Number
??
Dependencies
OpenGL 1.1 is required.
SGIX_color_range affects the definition of this extension.
Overview
This extension adds a new lighting stage to the OpenGL pipeline. This
stage occurs during fragment processing after the texture environment
has been applied and before fog has been applied. The extension
provides a mechanism for computing a post-texture specular lighting term.
This extension doesn't eliminate the specular term in vertex lighting, but
can be used to augment it. This extension provides the state framework for a
more general lighting model, but only includes the equation for computing
the specular contribution. The more general version is described in
SGIX_fragment_lighting.
Ct Cf
| |-------------------------------+
| | |
---------- |
| | |
| TexEnv | |
| | |
---------- |
| |
---------- |
| Clamp | Nf Lf Hf Ff |
---------- | | | | |
| ----------------- | FragmentColorMaterial
| | | v
Cf' | FragmentLight |--o-<- Material {Sm,...}
| | |
| -----------------
| |
| ---------
| | Clamp |
| ---------
| Cl |
| +----------------
v v
------------
| |
| SUM |
| |
------------
|
---------
| Clamp |
---------
|
Cf''
|
v
-------
| |
| Fog |
| |
-------
|
v
IP Status
Silicon Graphics has filed for patent protection for some of the
techniques described in this extension document.
Issues
* does this spec enable a reasonable evolution from a post-texture
specular highlight to a full blown per-pixel lighting computation?
* can we eliminate some commands and state now and allow the generality
to show up later? It doesn't seem like there is much harm in maintaining
extra state for computations that isn't actually used since it can be
maintained on the host. We eliminate the Lighting environment term
since it provides extra capability for how the lighting term is combined.
It can show up with the fragment_lighting extension.
* given the relaxation in the requirements for how the specular term is
computed, it is possible to support multiple specular lights but much
less likely to be able to support the same number of full blown fragment
lights.
void FragmentLightModeliSGIX(enum pname, int param);
void FragmentLightModelfSGIX(enum pname, float param);
void FragmentLightModelivSGIX(enum pname, int *params);
void FragmentLightModelfvSGIX(enum pname, float *params);
void FragmentLightiSGIX(enum light, enum pname, int param);
void FragmentLightfSGIX(enum light, enum pname, float param);
void FragmentLightivSGIX(enum light, enum pname, int *params);
void FragmentLightfvSGIX(enum light, enum pname, float *params);
void GetFragmentLightivSGIX(enum light, enum value, int *data);
void GetFragmentLightfvSGIX(enum light, enum value, float *data);
void FragmentMaterialfSGIX(enum face, enum pname, const float param);
void FragmentMaterialiSGIX(enum face, enum pname, const int param);
void FragmentMaterialfvSGIX(enum face, enum pname, const float *params);
void FragmentMaterialivSGIX(enum face, enum pname, const int *params);
void FragmentColorMaterialSGIX(enum face, enum mode);
void GetFragmentMaterialfvSGIX(enum face, enum pname, const float *data);
void GetFragmentMaterialivSGIX(enum face, enum pname, const int *data);
Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, by
the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and
GetDoublev:
FRAGMENT_LIGHTING_SGIX XXXX
FRAGMENT_COLOR_MATERIAL_SGIX XXXX
FRAGMENT_COLOR_MATERIAL_FACE_SGIX XXXX
FRAGMENT_COLOR_MATERIAL_PARAMETER_SGIX XXXX
Accepted by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv,
and GetDoublev:
MAX_FRAGMENT_LIGHTS_SGIX XXXX
MAX_ACTIVE_LIGHTS_SGIX XXXX
CURRENT_RASTER_NORMAL_SGIX XXXX
Accepted by the <light> parameter of FragmentLightfSGIX,
FragmentLightiSGIX, FragmentLightfvSGIX, and FragmentLightivSGIX, and by
the <cap> parameter of Enable, Disable, and IsEnabled, and by the <light>
parameter of GetFragmentLightfvSGIX and GetFragmentLightivSGIX:
FRAGMENT_LIGHT0_SGIX XXXX
.
.
.
FRAGMENT_LIGHT7_SGIX XXXX
Accepted by the <pname> parameter of FragmentLightModeliSGIX,
FragmentLightModelfSGIX, FragmentLightModelivSGIX,
FragmentLightModelfvSGIX, GetBooleanv, GetIntegerv, GetFloatv, and
GetDoublev:
FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX XXXX
FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX XXXX
FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX XXXX
FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX XXXX
Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation)
Section 2.12 Current Raster Position
... <paragraph 2>
The current raster position consists of three window coordinates xw, yw,
and zw, a clip corrdinate wc value, an eye coordinate distance, a valid
bit, and associated data consisting of a color, normal, and texture
coordinates. It is set ...
... <paragraph 5>
The current raster position requires five single-precision floating point
values for its xw, yw, and zw window coordinates, its wc clip coordinate,
and its eye coordinate distance, a single valid bit, a color (RGBA and color
index), normal, and texture coordinates for associated data. In the initial
state, the coordinates and texture coordinates are both (0,0,0,1), the eye
coordinate distance is 0, the valid bit is set, the associated RGBA color is
(1,1,1,1), the associated color index is 1, and the associated normal is
(0,0,1). In RGBA mode, the associated color index always has its initial
value; in color index mode, the RGBA color always maintains its initial
value.
Section 2.13 Colors and Coloring
...
Next vertex lighting, if enabled produces a color. If vertex lighting is
disabled, the current color is used in further processing. After vertex
lighting, RGBA colors are clamped to the range [0,1]. A color index is
converted to fixed-point and then its integer portion is masked (see
section 2.13.16). After clamping or masking, a primitive may be flatshaded,
indicating that all vertices of the primitive are to have the same color
(and normal). Finally, a primitive is clipped, then colors (texture
coordinates and normals) must be computed at the vertices introduced or
modified by clipping.
Additions to Chapter 3 of the 1.1 Specification (Rasterization)
Section 3.6.3 Rasterization of Pixel Rectangles
Conversion to Fragments
... <paragraph 2>
A fragment arising from a group consisting of color data takes on the color
index or color components of the group; the depth, normal and texture
coordinates are taken from the current raster position's associated data.
A fragment arising from a depth component takes the component's depth
value; the color, normal, and texture coordinate are given by those associated
with the current raster position. In both cases texture coordinates s, t,
and r are preplaced with s/q, t/q, and r/q, respectively. If q is less than
or equal to zero the results are undefined. Groups arising from DrawPixels
with a <format> of STENCIL_INDEX are treated specially and are described in
section 4.3.1.
Before Section 3.9 Fog insert:
Section 3.9 Fragment Lighting
If enabled, fragment lighting computes a color for each rasterized fragment
by applying an equation defined by a client-specified lighting model to
a collection of parameters that can include the fragment coordinates, the
coordinates of one or more light sources, the fragment normal, and
parameters defining the characteristics of the light source and current
fragment material. Fragment lighting is only defined for RGBA mode, it
has no effect in color index mode.
Fragment lighting may be in one of two states:
1. Lighting Off. In this state the color assigned to a fragment is the
rasterized fragment's post-texturing color.
2. Lighting On. In this state the color assigned to a fragment is the
result of summing the rasterized fragment's post-texturing color and
a color computed from the current fragment lighting parameters.
Fragment lighting is turned either on or off using the generic Enable or
Disable commands with the symbolic value FRAGMENT_LIGHTING_SGIX.
3.9.2 Lighting Operation
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
}
}
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)
Subset the equation to the specular term:
I[i] = Sm*Sl*(N.H_i)^n)
and
I' = SUM{i = 0 through Nf-1} I[i] (3.1)
Equation (3.1) is essentially the same as the specular term of the vertex
lighting equation described in section 2.13.1 for a single light source.
In order to compute the illumination terms for each fragment, the eye
coordinates of the fragment can be used to compute the light direction,
half angle vector, and attenuation factor in a manner similar to that used
in the vertex lighting computations. It is permissible for an
implementation to approximate these by computing these values as well as
the normal vector at the vertices and interpolating and renormalizing the
results, or by computing the entire equation at the vertices and
interpolating the color.
Fragment material state is maintained which is distinct from the
vertex material state. The fragment material state consists of
emission, ambient, diffuse, specular and shininess terms for both
the front and back face of a primitive though only the specular and
shininess terms are used by this extension. Unlike vertex lighting, the
fragment material state is constant across a primitive since
it is resolved during rasterization. The results of the back face
computation described in section 3.5.1 are used to determine whether
the front material or back material is used when two sided lighting
is enabled.
There is separate state for each fragment light source. The
fragment light source parameters are the same as the vertex light
source parameters described in section 2.13.1. The minimum number of
fragment light sources is 1. The number of available fragment light
sources can be queried by issuing the Get command with the <pname>
parameter set to MAX_FRAGMENT_LIGHTS_SGIX.
Distinct lighting model state is also maintained for vertex lighting and
fragment lighting. The lighting model state is described in section
2.13.1. Fragment lighting model state includes one additional parameter,
FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX, which controls how normals
are selected for use in the fragment lighting computations for a primitive.
If FLAT is selected for the lighting model, the normal from the provoking
vertex (as described in Section 2.13.7 Flatshading) of the primitive for all
fragment lighting computations for the primitive. If SMOOTH is specified
a normal is computed for each fragment using the normals from all of the
vertices of the primitive.
Fragment lighting differs from vertex lighting in that all components
of lighting parameters which are of type color in Table 2.7 are clamped
to the range [0,1] when they are specified.
Equation 3.2 is evaluated for each light source and the resulting
colors are summed. The resulting color components are clamped to the
range [0,1] and then passed to the lighting environment computation.
3.9.3 Lighting Parameter Specification
GetFragmentMaterialfvSGIX and GetFragmentMaterialivSGIX.
The fragment material state can be set with the commands
FragmentMaterialfSGIX, FragmentMaterialfvSGIX, FragmentMaterialiSGIX,
FragmentMaterialivSGIX using the values AMBIENT, DIFFUSE, SPECULAR,
SHININESS and EMISSION. This state can be queried using the commands
GetFragmentMaterialfvSGIX and GetFragmentMaterialivSGIX.
Lighting parameters for fragment light i can be modified by issuing the
commands FragmentLightfSGIX, FragmentLightiSGIX, FragmentLightfvSGIX, and
FragmentLightivSGIX with the <light> parameter
set to FRAGMENT_LIGHTi_SGIX. The lighting parameters for fragment light i
can be queried by issuing the commands GetFragmentLightfvSGIX and
GetFragmentLightivSGIX with the <light> parameter set to FRAGMENT_LIGHTi_SGIX.
Lighting model parameters for fragment lighting can be modified using the
commands FragmentLightModel{T}SGIX, FragmentLightModel{T}vSGIX. The
lighting model parameters can be queried by issuing the Get command <pname>
parameter set to the appropriate fragment lighting model parameter:
FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX, FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX,
FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX or FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX.
3.9.4 FragmentColorMaterial
It is possible to replace one or more fragment material properties terms in
Equation 3.1 with the fragment's pre-texturing color, causing these color
values to be used during the lighting computation. This behavior is enabled
and disabled by calling Enable and Disable with the symbolic value
FRAGMENT_COLOR_MATERIAL.
The command that controls which of these modes is selected is
void FragmentColorMaterial(enum face, enum mode);
<face> is one of FRONT, BACK, or FRONT_AND_BACK, indicating whether
the front material, back material, or both are affected by the
pre-texturing color. <mode> is one of EMISSION, AMBIENT, DIFFUSE,
SPECULAR, or AMBIENT_AND_DIFFUSE and specifies which material property
or properties are subsituted with the pre-texturing color. The substutions
do not affect the material state. When FragmentColorMaterial
is disabled the values in the fragment material state are used.
GetFragmentMaterial returns the fragment material last specified with
FragmentMaterial, regardless of whether FragmentColorMaterial is enabled.
Although all of the fragment material parameters may be substituted, only
substituting the SPECULAR material property will affect the result of
the lighting computation.
3.9.5 Interactions with Vertex Lighting
In order to allow implementions to share resources for vertex lighting and
fragment lighting, an implementation may limit the maximum number of combined
vertex and fragment lights to a number less than the sum of MAX_LIGHTS and
MAX_FRAGMENT_LIGHTS_SGIX. This limit can be queried using the Get command
with <pname> parameter MAX_ACTIVE_LIGHTS_SGIX. State for all
fragment and vertex lights is always maintained. When multiple
lights are enabled, priority is given to vertex lights starting with
LIGHT0 through LIGHT<n> where <n> is equal to MAX_LIGHTS, followed by
FRAGMENT_LIGHT0_SGIX through FRAGMENT_LIGHT<m>_SGIX where <m> is equal
to MAX_FRAGMENT_LIGHTS_SGIX.
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)
TBD
Additions to the GLX Specification
TBD
Dependencies on SGIX_color_range
If SGIX_color_range is implemented, then the components of lighting
parameters of type color, the result of evaluating the lighting
equation and the results of evaluating the lighting environment
are clamped to the extended color range rather than [0,1].
Errors
INVALID_ENUM is generated if FragmentMaterial{T}SGIX,
FragmentMaterial{T}vSGIX, or FragmentColorMaterialSGIX, parameter <face> is
not FRONT, BACK or FRONT_AND_BACK.
INVALID_ENUM is generated if FragmentMaterial{T}SGIX or
FragmentMaterial{T}vSGIX parameter <pname> is not AMBIENT, DIFFUSE,
SPECULAR, EMISSION, SHININESS, or AMBIENT_AND_DIFFUSE.
INVALID_ENUM is generated if GetFragmentMaterial{T}vSGIX parameter <face>
is not FRONT or BACK.
INVALID_ENUM is generated if GetFragmentMaterial{T}vSGIX parameter <pname>
is not AMBIENT, DIFFUSE, SPECULAR, EMISSION, or SHININESS,
INVALID_ENUM if FragmentColorMaterialSGIX parameter <mode> is not EMISSION,
AMBIENT, DIFFUSE, SPECULAR, or AMBIENT_AND_DIFFUSE
INVALID_ENUM if LightEnviSGIX parameter <pname> is not LIGHT_ENV_MODE_SGIX
or if parameter <mode> is not REPLACE, MODULATE, or ADD.
INVALID_ENUM is generated if FragmentLightModel{T}SGIX <pname> is not
FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX, FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX
or FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX or if
FragmentLightModel{T}vSGIX, parameter <pname> is not
FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX, FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX
FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX or
FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX.
INVALID_ENUM is generated if FragmentLight{T}SGIX, FragmentLight{T}vSGIX,
or GetFragmentLight{T}vSGIX parameter <light> is not FRAGMENT_LIGHT0_SGIX
... FRAGMENT_LIGHT<n>_SGIX where n is one minus the number of supported
fragment lights, or if FragmentLight{T}SGIX parameter <pname> is not
SPOT_EXPONENT, SPOT_CUTOFF, CONSTANT_ATTENUATION, LINEAR_ATTENUATION, or
QUADRATIC_ATTENUATION, or if FragmentLight{T}vSGIX or
GetFragmentLight{T}vSGIX parameter <pname> is not AMBIENT, DIFFUSE,
SPECULAR, POSITION, SPOT_DIRECTION, SPOT_EXPONENT, SPOT_CUTOFF,
CONSTANT_ATTENUATION, LINEAR_ATTENUATION, or QUADRATIC_ATTENUATION.
INVALID_VALUE is generated if FragmentLight{T}SGIX or FragmentLight{T}vSGIX
parameter <param> if a spot exponent value is specified outside the range
[0,128], or if spot cutoff is specified outside the range [0,90] (except
for the special value 180), or if a negative attenuation factor is
specified.
INVALID_OPERATION is generated if FragmentMaterial{T}SGIX,
FragmentMaterial{T}vSGIX, FragmentColorMaterialSGIX,
GetFragmentMaterial{T}vSGIX, LightEnviSGIX, FragmentLight{T}SGIX,
FragmentLight{T}vSGIX, FragmentLightModel{T}SGIX,
FragmentLightModel{T}vSGIX or GetFragmentLight{T}vSGIX is executed between
execution of Begin and the corresponding execution of End.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
FRAGMENT_LIGHTING_SGIX IsEnabled B False lighting/enable
FRAGMENT_COLOR_MATERIAL_SGIX IsEnabled B False lighting/enable
FRAGMENT_COLOR_MATERIAL_PARAMETER_SGIX GetIntegerv Z5 AMBIENT_AND_DIFFUSE lighting
FRAGMENT_COLOR_MATERIAL_FACE_SGIX GetIntegerv Z3 FRONT_AND_BACK lighting
AMBIENT GetFragmentMaterialfvSGIX 2xC (0.2,0.2,0.2,1.0) lighting
DIFFUSE GetFragmentMaterialfvSGIX 2xC (0.8,0.8,0.8,1.0) lighting
SPECULAR GetFragmentMaterialfvSGIX 2xC (0.0,0.0,0.0,1.0) lighting
EMISSION GetFragmentMaterialfvSGIX 2xC (0.0,0.0,0.0,1.0) lighting
SHININESS GetFragmentMaterialfvSGIX 2xR 0.0 lighting
FRAGMENT_LIGHT_MODEL_AMBIENT_SGIX GetFloatv C (0.2,0.2,0.2,0.2) lighting
FRAGMENT_LIGHT_MODEL_LOCAL_VIEWER_SGIX GetBooleanv B False lighting
FRAGMENT_LIGHT_MODEL_TWO_SIDE_SGIX GetBooleanv B False lighting
FRAGMENT_LIGHT_MODEL_NORMAL_INTERPOLATION_SGIX GetIntegerv Z2 SMOOTH lighting
AMBIENT GetFragmentLightfvSGIX 1*xC (0.0,0.0,0.0,1.0) lighting
DIFFUSE GetFragmentLightfvSGIX 1*xC see 3.x lighting
SPECULAR GetFragmentLightfvSGIX 1*xC see 3.x lighting
POSITION GetFragmentLightfvSGIX 1*xP (0.0,0.0,1.0,0.0) lighting
CONSTANT_ATTENUATION GetFragmentLightfvSGIX 1*xR 1.0 lighting
LINEAR_ATTENUATION GetFragmentLightfvSGIX 1*xR+ 0.0 lighting
QUADRATIC_ATTENUATION GetFragmentLightfvSGIX 1*xR+ 0.0 lighting
SPOT_DIRECTION GetFragmentLightfvSGIX 1*xD (0.0,0.0,-1.0) lighting
SPOT_EXPONENT GetFragmentLightfvSGIX 1*xR+ 0.0 lighting
SPOT_CUTOFF GetFragmentLightfvSGIX 1*xR+ 180.0 lighting
FRAGMENT_LIGHTi_SGIX IsEnabled 1*xB False lighting/enable
LIGHT_ENV_MODE_SGIX GetIntegerv Z3 REPLACE lighting
CURRENT_RASTER_NORMAL_SGIX GetFloatv N (0,0,1) current
New Implementation Dependent State
Get Value Get Command Type Minimum Value
--------- ----------- ---- -------------
MAX_FRAGMENT_LIGHTS_SGIX GetIntegerv Z+ 1
MAX_ACTIVE_LIGHTS_SGIX GetIntegerv z+ MAX_LIGHTS
Implementation Support
List of OpenGL implementations supporting the GL_SGIX_fragment_specular_lighting extension
Original File
Original text file for the GL_SGIX_fragment_specular_lighting extension
Page generated on Sun Nov 20 18:38:51 2005