blob: e2ae28ce6263f67f9c7b6e2ebb08491f4f79d236 [file] [log] [blame]
Name Strings
Bill Licea-Kane, AMD
Bruce Merry, ARM
Graham Sellers, AMD
Ian Romanick, Intel
Jeff Bolz, NVIDIA
Pat Brown, NVIDIA
Pierre Boudier, AMD
Graham Sellers, AMD (graham.sellers 'at'
Copyright (c) 2009-2013 The Khronos Group Inc. Copyright terms at
Specification Update Policy
Khronos-approved extension specifications are updated in response to
issues and bugs prioritized by the Khronos OpenGL Working Group. For
extensions which have been promoted to a core Specification, fixes will
first appear in the latest version of that core Specification, and will
eventually be backported to the extension document. This policy is
described in more detail at
Complete. Approved by the ARB on July 3, 2009.
Last Modified Date: 07/21/2009
Author revision: 4
ARB Extension #65
OpenGL 1.1 is required.
ARB_texture_cube_map is required.
EXT_texture_filter_anisotropic affects the definition of this extension.
This extension is written against the OpenGL 3.1 Specification.
When sampling from cube map textures, a three-dimensional texture
coordinate is used to select one of the cube map faces and generate
a two dimensional texture coordinate ( s t ), at which a texel is
sampled from the determined face of the cube map texture. Each face
of the texture is treated as an independent two-dimensional texture,
and the generated ( s t ) coordinate is subjected to the same
clamping and wrapping rules as for any other two dimensional texture
Although it is unlikely that the generated ( s t ) coordinate lies
significantly outside the determined cube map face, it is often the
case that the locations of the individual elements required during a
linear sampling do not lie within the determined face, and their
coordinates will therefore be modified by the selected clamping and
wrapping rules. This often has the effect of producing seams or
other discontinuities in the sampled texture.
This extension allows implementations to take samples from adjacent
cube map faces, providing the ability to create seamless cube maps.
IP Status
New Procedures and Functions
New Tokens
Accepted by the <cap> parameter of Enable, Disable and IsEnabled,
and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv
and GetDoublev:
Additions to Chapter 3 of the 3.1 Specification (Rasterization)
Section 3.8.7, Cube Map Texture Selection, p. 143, change the last
paragraph from
"This new ( s t ) is used to find a texture value in the determined
face's two-dimensional texture image using the rules given in
sections 3.8.7 through 3.8.9."
Seamless Cube Map Filtering
Seamless cube map filtering is enabled or disabled by calling Enable
or Disable, respectively, with the symbolic constant
When seamless cube map filtering is disabled, the new (s t) is used
to find a texture value in the determined face's two-dimensional
image using the rules given in sections 3.8.9 through 3.8.10.
When seamless cube map filtering is enabled, the rules for texel
selection in sections 3.8.9 through 3.8.10 are modified so that
texture wrap modes are ignored. Instead,
* If NEAREST filtering is done within a miplevel, always apply wrap
* If LINEAR filtering is done within a miplevel, always apply wrap mode
o If a texture sample location would lie in the texture border in
either u or v, instead select the corresponding texel from the
appropriate neighboring face.
o If a texture sample location would lie in the texture border in
both u and v (in one of the corners of the cube), there is no
unique neighboring face from which to extract one texel. The
recommended method is to average the values of the three
available samples. However, implementations are free to
construct this fourth texel in another way, so long as, when the
three available samples have the same value, this texel also has
that value.
The required state is one bit indicating whether seamless cube map
filtering is enabled or disabled. Initially, it is disabled.
Add final paragraphs to Section 3.8.7
"When TEXTURE_MAX_ANISOTROPY_EXT is greater than 1.0, an
implementation may sample from the texture at multiple locations in
order to produce a filtered texel value. In this case, some of the
required samples may lie outside the determined cube map face. If
TEXTURE_CUBE_MAP_SEAMLESS is enabled, it is implementation defined
as to whether these samples are taken from the determined face, or
from the appropriate adjacent cube map face."
Dependencies on EXT_texture_filter_anisotropic
If EXT_texture_filter_anisotropic is not supported, remove the
final paragraph added to Section 3.8.6 which references
New State
In table 6.42, Miscellaneous, p. 279, add the following:
Get Value Type Get Command Init Val Description Sec. Attribute
--------------------------- ------ -------------------- -------- -------------------------- ------ ---------
TEXTURE_CUBE_MAP_SEAMLESS B IsEnabled FALSE Seamless cube map filtering 3.8.6 -
New Implementation Dependent State
1) Should this be a new wrap mode, or a separate state?
RESOLVED: It cannot be a normal wrap mode because it does not
apply per dimension, but rather to a texture as a whole.
Therefore, it is a separate state item.
2) What is the interaction with anisotropic filtering as described
in EXT_texture_filter_anisotropic?
RESOLVED: EXT_texture_filter_anisotropic leaves the
implementation of anisotropic filtering implementation defined.
Therefore, this extension does the same.
3) Should this be per-texture, or a global state?
RESOLVED: While in some cases it may be desirable to mix seamless
and non-seamless cube map texture sampling, it is sufficient to
leave this spec defining a global state and provide per-texture
support in another extension.
Revision History
Rev. Date Author Changes
---- -------- -------- -----------------------------------------
4 07/21/09 Jon Leech Reformat to 80 columns and update
ambiguous sample location to match
the 3.2 spec (bug 5357).
3 07/20/09 Jon Leech Assign enum value and remove _ARB suffix.
2 07/01/09 wwlk Updated per bug 5292.
Re-written against the OpenGL 3.1 specification.
1 05/07/09 gsellers Initial draft based on