blob: 9a591b3f6175e549f8caa78ee6c547d86d2c89a8 [file] [log] [blame]
Name
SGIX_texture_scale_bias
Name Strings
GL_SGIX_texture_scale_bias
Version
$Date: 1997/02/26 03:36:38 $ $Revision: 1.9 $
Number
56
Dependencies
EXT_texture
EXT_texture3D
EXT_texture_object
Overview
This extension adds scale, bias, and clamp to [0, 1] operations to the
texture pipeline.
These operations are applied to the filtered result of a texture lookup,
before that result is used in the texture environment equations and
before the texture color lookup table of SGI_texture_color_table,
if that extension exists.
These operations are distinct from the scale, bias, and clamp operations
that appear in the SGI_color_table extension, which are used to
define a color lookup table.
Scale and bias operations on texels can be used to better utilize the
color resolution of a particular texture internal format (see EXT_texture).
Issues
* still missing: GLX protocol, registry number
* RE and IMPACT do not have hardware support for this extension.
New Procedures and Functions
None
New Tokens
Accepted by the <pname> parameters of TexParameterfv, TexParameteriv,
and GetTexParameter:
POST_TEXTURE_FILTER_BIAS_SGIX 0x8179
POST_TEXTURE_FILTER_SCALE_SGIX 0x817A
Accepted by the <pname> parameters of GetBooleanv, GetDoublev, GetFloatv,
and GetIntegerv:
POST_TEXTURE_FILTER_BIAS_RANGE_SGIX 0x817B
POST_TEXTURE_FILTER_SCALE_RANGE_SGIX 0x817C
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
None
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
A scale or bias is specified using TexParameterfv or
TexParameteriv with a <pname> of either POST_TEXTURE_FILTER_SCALE_SGIX
or POST_TEXTURE_FILTER_BIAS_SGIX and with <params> set to an array of
four values. The scale or bias values can be queried using
GetTexParameterfv or GetTexParameteriv.
The scale, bias, and clamp operations are applied, in that order,
directly before the texture environment equations, or, if the
SGI_texture_color_table extension exists, directly before the
texture color lookup table.
The four values for scale (or bias) correspond to the R, G, B,
and A scale (or bias) factors.
These are applied to the corresponding texture components, Rt, Gt,
Bt, and At, as denoted in the EXT_texture extension.
Following the scale and bias is a clamp to [0, 1].
The scale, bias, and clamp operations are effectively disabled by
setting the four scale values to 1 and the four bias values to 0.
There is no specific enable or disable token for this extension.
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the
Frame Buffer)
None
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
None
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
The specification for "EXT_texture_object" describes the state that
comprises a texture object. Here it is rewritten to include the
scale and bias state:
"A texture object comprises the image arrays, priority, border color,
filter modes, and wrap modes that are associated with that object. More
explicitly, the state list
TEXTURE,
TEXTURE_PRIORITY_EXT
TEXTURE_RED_SIZE,
TEXTURE_GREEN_SIZE,
TEXTURE_BLUE_SIZE,
TEXTURE_ALPHA_SIZE,
TEXTURE_LUMINANCE_SIZE,
TEXTURE_INTENSITY_SIZE,
TEXTURE_WIDTH,
TEXTURE_HEIGHT,
TEXTURE_DEPTH_EXT,
TEXTURE_BORDER,
TEXTURE_COMPONENTS,
TEXTURE_BORDER_COLOR,
TEXTURE_MIN_FILTER,
TEXTURE_MAG_FILTER,
TEXTURE_WRAP_S,
TEXTURE_WRAP_T,
TEXTURE_WRAP_R_EXT,
POST_TEXTURE_FILTER_BIAS_SGIX,
POST_TEXTURE_FILTER_SCALE_SGIX
composes a single texture object."
Since an implementation may have a limited range for the values of scale
and bias (e.g. due to hardware constraints), this range can be queried.
The scale or bias range is obtained using GetFloatv (or other Get) with a
<value> of POST_TEXTURE_FILTER_SCALE_RANGE_SGIX or
POST_TEXTURE_FILTER_BIAS_RANGE_SGIX, respectively. An array of two floats
is returned. The first is the minimum value and the second is the maximum
value.
Additions to the GLX Specification
None
GLX Protocol
XXX
Dependencies on EXT_texture
This extension refers to texture components as Rt, Gt, Bt, and At,
as denoted in the EXT_texture extension.
Dependencies on EXT_texture3D
If EXT_texture3D is not implemented, references to it should be deleted.
Dependencies on EXT_texture_object
As described above, the scale and bias state is included as part of the
texture object state.
If EXT_texture_object is not implemented, references to it should be deleted.
Errors
POST_TEXTURE_FILTER_BIAS_SGIX and POST_TEXTURE_FILTER_SCALE_SGIX are added
to the list of <pname> parameters that are accepted by TexParameter[fi]v
and GetTexParameter[fi]v. POST_TEXTURE_FILTER_BIAS_RANGE_SGIX and
POST_TEXTURE_FILTER_SCALE_RANGE_SGIX are added to the list of <value>
parameters that are accepted by Get.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
POST_TEXTURE_FILTER_BIAS_SGIX GetTexParameterfv n x 4 x R (0,0,0,0) texture
POST_TEXTURE_FILTER_SCALE_SGIX GetTexParameterfv n x 4 x R (1,1,1,1) texture
Note: The "Type" column shows "n x ..." since this state will appear
in each of "n" texture objects defined by EXT_texture_object.
If EXT_texture_object is not implemented, then this state will appear
for each texture dimension (e.g. TEXTURE_1D, TEXTURE_2D, ...).
New Implementation Dependent State
Get Value Get Command Type Minimum Value Attribute
--------- ----------- ---- ------------- ---------
POST_TEXTURE_FILTER_BIAS_RANGE_SGIX GetFloatv 2 x R (0,1) -
POST_TEXTURE_FILTER_SCALE_RANGE_SGIX GetFloatv 2 x R (0,1) -
Note: The "Minimum Value" for POST_TEXTURE_FILTER_BIAS_RANGE_SGIX and
POST_TEXTURE_FILTER_SCALE_RANGE_SGIX is listed as a range, which might seem
confusing. What is meant is that an implementation will support at least
the range listed.