detail_texture
Specification
Name
SGIS_detail_texture
Name Strings
GL_SGIS_detail_texture
Version
$Date: 1996/09/09 00:59:08 $ $Revision: 1.2 $
Number
2
Dependencies
EXT_texture is required
EXT_subtexture affects the definition of this extension
EXT_copy_texture affects the definition of this extension
EXT_texture_object affects the definition of this extension
Overview
This extension introduces texture magnification filters that blend
between the level 0 image and a separately defined "detail" image.
The detail image represents the characteristics of the high frequency
subband image above the band-limited level 0 image. The detail image is
typically a rectangular portion of the subband image which is modified
so that it can be repeated without discontinuities along its edges.
Detail blending can be enabled for all color channels, for the alpha
channel only, or for the red, green, and blue channels only. It is
available only for 2D textures.
WARNING - Silicon Graphics has filed for patent protection for some
of the techniques described in this extension document.
Issues
* Should detail textures be supported in 1D? 3D? (Currently
written to support 2D only)
* Is there any need to support detail textures with NEAREST
or FILTER4 filtering? (No)
* How does detail texture interact with a texture whose
minimum LOD image is not layer zero? (Handle this in the LOD
extension.)
* Should six detail filters be defined, so that the MODE is part
of the filter name? (LINEAR_ADD_DETAIL_SGIS,
LINEAR_ADD_DETAIL_ALPHA_SGIS, ...) (No)
* I have scaled and biased the detail texture value to the range [-1,1]
in this specification. I believe that Iris GL scaled and biased to
[-0.5,0.5]. The [-1,1] range seems clearer to me, if it allows F()
to be limited to [0,1]. Is this acceptable?
* Should detail texture objects and 2D texture objects be separate
sets, or should it be possible to use the same texture object both
as a detail texture and as a 2D texture? (Keep them separate)
New Procedures and Functions
void DetailTexFuncSGIS(enum target,
sizei n,
const float* points);
void GetDetailTexFuncSGIS(enum target,
float* points);
New Tokens
Accepted by the < target > parameters of GetTexImage,
GetTexLevelParameterfv, GetTexLevelParameteriv, GetTexParameterfv,
GetTexParameteriv, TexImage2D, TexParameterf, TexParameterfv,
TexParameteri, and TexParameteriv. If the corresponding extensions are
supported, also accepted by the < target > parameters of TexSubImage2DEXT,
CopyTexImage2DEXT, CopyTexSubImage2DEXT, and BindTextureEXT:
DETAIL_TEXTURE_2D_SGIS
Accepted by the < pname > parameters of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev:
DETAIL_TEXTURE_2D_BINDING_SGIS
Accepted by the < param > parameter of TexParameteri and TexParameterf,
and by the < params > parameter of TexParameteriv and TexParameterfv,
when their < pname > parameter is TEXTURE_MAG_FILTER:
LINEAR_DETAIL_SGIS
LINEAR_DETAIL_ALPHA_SGIS
LINEAR_DETAIL_COLOR_SGIS
Accepted by the < pname > parameter of TexParameteri, TexParameterf,
TexParameteriv, TexParameterfv, GetTexParameteriv, and GetTexParameterfv:
DETAIL_TEXTURE_LEVEL_SGIS
DETAIL_TEXTURE_MODE_SGIS
Accepted by the < pname > parameter of GetTexParameteriv and
GetTexParameterfv:
DETAIL_TEXTURE_FUNC_POINTS_SGIS
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
None
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
GL Specification Table 3.7 is updated as follows:
Name Type Legal Values
---- ---- ------------
TEXTURE_WRAP_S integer CLAMP, REPEAT
TEXTURE_WRAP_T integer CLAMP, REPEAT
TEXTURE_WRAP_R_EXT integer CLAMP, REPEAT
TEXTURE_MIN_FILTER integer NEAREST, LINEAR,
NEAREST_MIPMAP_NEAREST,
NEAREST_MIPMAP_LINEAR,
LINEAR_MIPMAP_NEAREST,
LINEAR_MIPMAP_LINEAR,
FILTER4_SGIS
TEXTURE_MAG_FILTER integer NEAREST, LINEAR,
FILTER4_SGIS,
LINEAR_DETAIL_SGIS,
LINEAR_DETAIL_ALPHA_SGIS,
LINEAR_DETAIL_COLOR_SGIS
TEXTURE_BORDER_COLOR 4 floats any 4 values in [0,1]
DETAIL_TEXTURE_LEVEL_SGIS integer any non-positive integer
DETAIL_TEXTURE_MODE_SGIS integer ADD, MODULATE
Table 3.7: Texture parameters and their values.
3.8.2.1 Texture magnification with detail
Three additional texture magnification filters are defined for texture
magnification. These values, which are assigned to TEXTURE_MAG_FILTER,
are LINEAR_DETAIL_SGIS, LINEAR_DETAIL_ALPHA_SGIS, and
LINEAR_DETAIL_COLOR_SGIS. All three filters sample the level zero
texture array exactly as it would be sampled with filter mode LINEAR.
All three also sample the level zero texture array of a second
texture, known as the detail texture, when three conditions are met.
The detail texture corresponding to texture TEXTURE_2D is
DETAIL_TEXTURE_2D_SGIS. The conditions are:
1. The active texture must be TEXTURE_2D.
2. The internal formats of TEXTURE_2D and DETAIL_TEXTURE_2D_SGIS
must have been specified identically.
3. The level 0 array of DETAIL_TEXTURE_2D_SGIS must have nonzero width
and height.
If these conditions are not met, it is as though the magnification
texture filter was LINEAR. (Although querying the magnification filter
value will return the value as specified.) If they are met, the level
zero array of the detail texture is also linearly sampled, using the
following arithmetic:
n = log base 2 of the width of the level zero array of TEXTURE_2D
m = log base 2 of the height of the level zero array of TEXTURE_2D
N = log base 2 of the width of DETAIL_TEXTURE_2D_SGIS
M = log base 2 of the height of DETAIL_TEXTURE_2D_SGIS
L = DETAIL_TEXTURE_LEVEL_SGIS value of TEXTURE_2D
u = s * 2**(n-L)
v = t * 2**(m-L)
i0 = floor(u - 1/2) mod 2**N
j0 = floor(v - 1/2) mod 2**M
i1 = (i0 + 1) mod 2**N
j1 = (j0 + 1) mod 2**M
A = frac(u - 1/2)
B = frac(v - 1/2)
Tdetail = (1-A) * (1-B) * detail[i0,j0] +
A * (1-B) * detail[i1,j0] +
(1-A) * B * detail[i0,j1] +
A * B * detail[i1,j1]
Note that magnification corresponds to negative values of level-of-detail
and minification corresponds to positive values. Hence L, the value of the
DETAIL_TEXTURE_LEVEL_SGIS parameter of TEXTURE_2D, must be negative. The
absolute value of L can be thought of as the number of levels that
separate the level 0 image of TEXTURE_2D and the image of
DETAIL_TEXTURE_2D, which is replicated as necessary to fill the appropriate
number of texels. For example, if L is -2, the detail texture image is
replicated as necessary in x and y to form a single image whose dimensions
are four times larger than the level zero array of TEXTURE_2D.
The texture value computed from the primary texture (Ttexture) and
the value computed from the detail texture (Tdetail) are combined
in one of two ways to compute the final texture value (T). The
values of Ttexture, Tdetail, and T are treated as though they range
from 0.0 through 1.0 in these equations.
If DETAIL_TEXTURE_MODE_SGIS of TEXTURE_2D is ADD, then
T' = Ttexture + F(LOD) * (2*Tdetail-1)
/ 0 T' < 0
T = < T' 0 <= T' <= \ 1 T' >
where F is a function of the level-of-detail parameter LOD, which is
represented by the Greek character lambda in the GL specification. In
effect, the detail texture is scaled and biased so that its range is
[-1,1]. The resulting signed value is scaled by a function of LOD,
added to the base texture, and clamped to [0,1].
If DETAIL_TEXTURE_MODE_SGIS or TEXTURE_2D is MODULATE, then
T' = Ttexture * (1 + F(LOD) * (2*Tdetail-1))
/ 0 T' < 0
T = < T' 0 <= T' <= \ 1 T' >
Here again the detail texture is scaled and biased so that its range
is [-1,1]. The resulting signed value is scaled by a function of LOD,
and biased by 1. This result scales the base texture, which is then
clamped to [0,1].
The function F of level-of-detail parameter LOD is specified by calling
DetailTexFuncSGIS with < target > set to TEXTURE_2D, < points > pointing at
an array of pairs of floating point values, and < n > set to the number
of value pairs in < points >. The first value of each value pair in
< points > specifies a value of LOD, and the second value of each value
pair specifies the corresponding function value. The order in which
the points are specified is not significant. The < n > value pairs in
< points > completely specify the function, replacing any previous
specification that may have existed. Since negative values of LOD
correspond to magnification and positive values correspond to
minification, the points should have negative values for LOD (though it
is not an error to specify positive values).
Function F is evaluated by sorting the value pairs specified by
DetailTexFuncSGIS by LOD value, then fitting a curve through these
points. This curve may be linear between adjacent points, or it may be
smoothed, but it will pass exactly through the points, limited only by
the resolution of the implementation. The value pair with the lowest
LOD value specifies the function value F for all values of LOD less than
or equal to that pair's LOD. Likewise, the value pair with the greatest
LOD value specifies the function value F for all values of LOD greater
than or equal to that pair's LOD. F is undefined if two or more value
pairs have the same LOD value.
If the texture magnification filter is LINEAR_DETAIL_SGIS, then both
the color and the alpha components of T are computed as described
in the equations above. If the filter is LINEAR_DETAIL_COLOR_SGIS,
then all components of T other than alpha are computed as described
above, and the alpha component of T is computed as if the texture
magnification filter were LINEAR. Finally, if the filter is
LINEAR_DETAIL_ALPHA_SGIS, the alpha component of T is computed as
described in the equations above, and all other components of T
are computed as if the texture magnification filter were LINEAR.
All OpenGL texture commands that accept a target value of TEXTURE_2D
also accept the target value DETAIL_TEXTURE_2D_SGIS. These commands
operate on and return state of the detail texture just as they do
of the 2-dimensional texture.
If EXT_texture_object is supported, detail texture objects can be
created, operated on, and bound just as their 2D counterparts are. The
sets of detail textures and 2D textures are exclusive, however, so it
is not possible to use a texture object both as a 2D texture and as
a detail texture. By default zero is bound to DETAIL_TEXTURE_2D_SGIS,
just as zero is bound to TEXTURE_2D.
Specification of a detail texture
---------------------------------
A detail texture is specified by calling TexImage2D or CopyTexImage2DEXT
with < target > set to DETAIL_TEXTURE_2D_SGIS, < level > set to 0, < border >
set to 0, and the other parameters specified to generate the desired
image.
Minification vs. Magnification
------------------------------
If the magnification filter is given by LINEAR_DETAIL_SGIS,
LINEAR_DETAIL_ALPHA_SGIS, or LINEAR_DETAIL_COLOR_SGIS, and the
minification filter is given by NEAREST_MIPMAP_NEAREST or
LINEAR_MIPMAP_NEAREST, then c = 0.5. The parameter c is used to
determine whether minification or magnification filtering is done,
as described in Section 3.8.2 of the GL Specification (Texture
Magnification).
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Framebuffer)
None
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
GetDetailTexFuncSGIS is not included in display lists.
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
Although many of the parameter values of a detail texture have no
effect on texture operation, they are maintained and may be queried.
There is no value associated with the binding point
DETAIL_TEXTURE_2D_SGIS, so it is not accepted as the < pname > parameter
of GetBooleanv, GetIntegerv, GetFloatv, or GetDoublev. The name of
the detail texture that is bound to DETAIL_TEXTURE_2D_SGIS is queried
by calling GetBooleanv, GetIntegerv, GetFloatv, or GetDoublev with
< pname > set to DETAIL_TEXTURE_2D_BINDING_SGIS. Zero is returned if
no texture has been bound.
The number of points in the detail texture function specification of
a texture is queried by calling GetTexParameteriv or GetTexParameterfv
with < target > set to the target of the desired texture and < pname > set
to DETAIL_TEXTURE_FUNC_POINTS_SGIS. The function
GetDetailTexFuncSGIS returns in < points > all of the points in the detail
texture function of texture < target >.
Additions to the GLX Specification
None
Dependencies on EXT_texture
EXT_texture is required.
Dependencies on EXT_texture3D
None, because detail texture is not specified for 3D textures. This
extensions is designed to allow a subsequent extension to define 3D
detail textures, however.
Dependencies on EXT_subtexture
If EXT_subtexture is not implemented, then the references to
TexSubImage2DEXT and CopyTexSubImage2DEXT in this file are invalid,
and should be ignored.
Dependencies on EXT_copy_texture
If EXT_copy_texture is not implemented, then the references to
CopyTexImage2DEXT and CopyTexSubImage2DEXT in this file are invalid,
and should be ignored.
Dependencies on EXT_texture_object
If EXT_texture_object is not implemented, then the references to
BindTextureEXT are invalid, and should be ignored.
If EXT_texture_object is implemented, the state values named
DETAIL_TEXTURE_LEVEL_SGIS
DETAIL_TEXTURE_MODE_SGIS
DETAIL_TEXTURE_FUNC_POINTS_SGIS
< DETAIL_TEXTURE_FUNC >
are added to the state vector of each texture object. When an attribute
set that includes texture information is popped, the bindings and
enables are first restored to their pushed values, then the bound
textures have their detail parameters restored to their pushed values.
Errors
INVALID_VALUE is generated if TexImage2D or CopyTexImage2DEXT
parameter < target > is DETAIL_TEXTURE_2D_SGIS, and parameter < level >
or parameter < border > is not zero.
INVALID_VALUE is generated if BindTextureEXT parameter < target > is
DETAIL_TEXTURE_2D_SGIS, and parameter < texture > is not the name of a
detail texture, the name of an as yet unbound texture, or zero.
INVALID_VALUE is generated if TexParameteri, TexParameterf,
TexParameteriv, or TexParameterfv parameter < pname > is
DETAIL_TEXTURE_MODE_SGIS, and parameter < param > is not ADD or MODULATE,
or parameter < params > doesn't point to ADD or MODULATE.
INVALID_VALUE is generated if TexParameteri, TexParameterf,
TexParameteriv, or TexParameterfv parameter < pname > is
DETAIL_TEXTURE_LEVEL_SGIS, and parameter < param > is positive,
or parameter < params > points to a positive value.
INVALID_ENUM is generated if DetailTexFuncSGIS or
GetDetailTexFuncSGIS parameter < target > is not TEXTURE_2D.
INVALID_VALUE is generated if DetailTexFuncSGIS parameter < n > is
negative.
INVALID_OPERATION is generated if DetailTexFuncSGIS or
GetDetailTexFuncSGIS is executed between execution of Begin and the
corresponding execution to End.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
DETAIL_TEXTURE_2D_BINDING_SGIS GetIntegerv Z+ 0 texture
DETAIL_TEXTURE_LEVEL_SGIS GetTexParameteriv n x Z- -4 texture
DETAIL_TEXTURE_MODE_SGIS GetTexParameteriv n x Z2 ADD texture
DETAIL_TEXTURE_FUNC_POINTS_SGIS GetTexParameteriv n x Z+ 2 texture
< DETAIL_TEXTURE_FUNC > GetDetailTexFuncSGIS n x m x R {0, 0}, {-4, 1} texture
New Implementation Dependent State
None