OES_texture_cube_map

GL_OES_texture_cube_map

Benj Lipchak (benj.lipchak 'at' amd.com)

Copyright (c) 2007-2013 The Khronos Group Inc. Copyright terms at
    http://www.khronos.org/registry/speccopyright.html

Khronos-approved extension specifications are updated in response to
issues and bugs prioritized by the Khronos OpenGL ES 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
    https://www.khronos.org/registry/OpenGL/docs/update_policy.php

Ratified by the Khronos BOP

Version 2, April 16, 2015

OpenGL ES Extension #20

OpenGL ES 1.0 is required.

This extension is based on the ARB_texture_cube_map extension specification.

This extension provides a new texture generation scheme for cube
map textures.  Instead of the current texture providing a 1D, 2D,
or 3D lookup into a 1D, 2D, or 3D texture image, the texture is a
set of six 2D images representing the faces of a cube.  The (s,t,r)
texture coordinates are treated as a direction vector emanating from
the center of a cube.  At texture generation time, the interpolated
per-fragment (s,t,r) selects one cube face 2D image based on the
largest magnitude coordinate (the major axis).  A new 2D (s,t) is
calculated by dividing the two other coordinates (the minor axes
values) by the major axis value.  Then the new (s,t) is used to
lookup into the selected 2D texture image face of the cube map.

Unlike a standard 1D, 2D, or 3D texture that have just one target,
a cube map texture has six targets, one for each of its six 2D texture
image cube faces.  All these targets must be consistent, complete,
and have equal width and height (ie, square dimensions).

This extension also provides two new texture coordinate generation modes
for use in conjunction with cube map texturing.  The reflection map
mode generates texture coordinates (s,t,r) matching the vertex's
eye-space reflection vector.  The reflection map mode
is useful for environment mapping without the singularity inherent
in sphere mapping.  The normal map mode generates texture coordinates
(s,t,r) matching the vertex's transformed eye-space
normal.  The normal map mode is useful for sophisticated cube
map texturing-based diffuse lighting models.

The intent of the new texgen functionality is that an application using
cube map texturing can use the new texgen modes to automatically
generate the reflection or normal vectors used to look up into the
cube map texture.

An application note:  When using cube mapping with dynamic cube
maps (meaning the cube map texture is re-rendered every frame),
by keeping the cube map's orientation pointing at the eye position,
the texgen-computed reflection or normal vector texture coordinates
can be always properly oriented for the cube map.  However if the
cube map is static (meaning that when view changes, the cube map
texture is not updated), the texture matrix must be used to rotate
the texgen-computed reflection or normal vector texture coordinates
to match the orientation of the cube map.  The rotation can be
computed based on two vectors: 1) the direction vector from the cube
map center to the eye position (both in world coordinates), and 2)
the cube map orientation in world coordinates.  The axis of rotation
is the cross product of these two vectors; the angle of rotation is
the arcsin of the dot product of these two vectors.

Please refer to the ARB_texture_cube_map extension specification.

    void glTexGenfOES(GLenum coord, GLenum pname, GLfloat param);
    void glTexGenfvOES(GLenum coord, GLenum pname, const GLfloat *params);
    void glTexGeniOES(GLenum coord, GLenum pname, GLint param);
    void glTexGenivOES(GLenum coord, GLenum pname, const GLint *params);
    void glTexGenxOES(GLenum coord, GLenum pname, GLfixed param);
    void glTexGenxvOES(GLenum coord, GLenum pname, const GLfixed *params);

    void glGetTexGenfvOES(GLenum coord, GLenum pname, GLfloat *params);
    void glGetTexGenivOES(GLenum coord, GLenum pname, GLint *params);
    void glGetTexGenxvOES(GLenum coord, GLenum pname, GLfixed *params);

Accepted by the <pname> parameter of TexGenfOES, TexGeniOES, TexGenxOES,
TexGenfvOES, TexGenivOES, TexGenxvOES, GetTexGenfvOES, GetTexGenivOES, and
GetTexGenxvOES:

    TEXTURE_GEN_MODE_OES                0x2500

Accepted by the <params> parameter of TexGenfOES, TexGeniOES, TexGenxOES,
TexGenfvOES, TexGenivOES, and TexGenxvOES when <pname> parameter is
TEXTURE_GEN_MODE_OES:

    NORMAL_MAP_OES                      0x8511
    REFLECTION_MAP_OES                  0x8512

Accepted by the <cap> parameter of Enable, Disable, IsEnabled, by the
<pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and GetFixedv, and
by the <target> parameter of BindTexture, GetTexParameterfv, 
GetTexParameteriv, GetTexParameterxv, TexParameterf, TexParameteri,
TexParameterx, TexParameterfv, TexParameteriv, and TexParameterxv:

    TEXTURE_CUBE_MAP_OES                0x8513

Accepted by the <cap> parameter of Enable, Disable, IsEnabled, by the
<pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and GetFixedv, and
by the <coord> parameter of TexGenfOES, TexGeniOES, TexGenxOES, TexGenfvOES, 
TexGenivOES, TexGenxvOES, GetTexGenfvOES, GetTexGenivOES, and
GetTexGenxvOES:

    TEXTURE_GEN_STR_OES                 0x8D60

Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev:

    TEXTURE_BINDING_CUBE_MAP_OES        0x8514

Accepted by the <target> parameter of TexImage2D, CopyTexImage2D, 
TexSubImage2D, and CopySubTexImage2D:

    TEXTURE_CUBE_MAP_POSITIVE_X_OES     0x8515
    TEXTURE_CUBE_MAP_NEGATIVE_X_OES     0x8516
    TEXTURE_CUBE_MAP_POSITIVE_Y_OES     0x8517
    TEXTURE_CUBE_MAP_NEGATIVE_Y_OES     0x8518
    TEXTURE_CUBE_MAP_POSITIVE_Z_OES     0x8519
    TEXTURE_CUBE_MAP_NEGATIVE_Z_OES     0x851A

Accepted by the <pname> parameter of GetBooleanv, GetDoublev,
GetIntegerv, and GetFloatv:

    MAX_CUBE_MAP_TEXTURE_SIZE_OES       0x851C

  Change the last sentence in the 1st paragraph (page 37) to:

  "If <pname> is TEXTURE_GEN_MODE_OES, then either <params> points to
  or <param> is an integer that is one of the symbolic constants
  REFLECTION_MAP_OES, or NORMAL_MAP_OES."  OBJECT_LINEAR, EYE_LINEAR, 
  and SPHERE_MAP texture coordinate generation modes are not supported.

  Add these paragraphs after the 4th paragraph (page 38):

  "If TEXTURE_GEN_MODE_OES indicates REFLECTION_MAP_OES, compute the
  reflection vector r as described for the SPHERE_MAP mode.  Then the
  value assigned to an s coordinate is s = rx; the value assigned to a t
  coordinate is t = ry; and the value assigned to a r coordinate is r = rz.

  If TEXTURE_GEN_MODE_OES indicates NORMAL_MAP_OES, compute the normal
  vector nf as described in section 2.10.3.  Then the value assigned
  to an s coordinate is s = nfx; the value assigned to a t coordinate is
  t = nfy; and the value assigned to a r coordinate is r = nfz.  (The values
  nfx, nfy, and nfz are the components of nf.)

  A texture coordinate generation function is enabled or disabled
  using Enable and Disable with an argument of TEXTURE_GEN_STR_OES.  
  TEXTURE_GEN_S, TEXTURE_GEN_T, TEXTURE_GEN_R and TEXTURE_GEN_Q
  argument values to Enable and Disable are not supported.

  The last paragraph's last sentence (page 38) should be changed to:

  "Initially all texture generation modes are set to REFLECTION_MAP_OES"

 Change the second and third to last sentences on page 116 to:

 "<target> must be one of TEXTURE_2D for a 2D texture, or one of
 TEXTURE_CUBE_MAP_POSITIVE_X_OES, TEXTURE_CUBE_MAP_NEGATIVE_X_OES,
 TEXTURE_CUBE_MAP_POSITIVE_Y_OES, TEXTURE_CUBE_MAP_NEGATIVE_Y_OES,
 TEXTURE_CUBE_MAP_POSITIVE_Z_OES, or TEXTURE_CUBE_MAP_NEGATIVE_Z_OES
 for a cube map texture."

 Add the following paragraphs after the first paragraph on page 117:

 "A 2D texture consists of a single 2D texture image.  A cube
 map texture is a set of six 2D texture images.  The six cube map
 texture targets form a single cube map texture though each target
 names a distinct face of the cube map.  The TEXTURE_CUBE_MAP_*_OES
 targets listed above update their appropriate cube map face 2D
 texture image.  Note that the six cube map 2D image tokens such as
 TEXTURE_CUBE_MAP_POSITIVE_X_OES are used when specifying, updating,
 or querying one of a cube map's six 2D image, but when enabling
 cube map texturing or binding to a cube map texture object (that is
 when the cube map is accessed as a whole as opposed to a particular
 2D image), the TEXTURE_CUBE_MAP_OES target is specified.

 When the target parameter to TexImage2D is one of the six cube map
 2D image targets, the error INVALID_VALUE is generated if the width
 and height parameters are not equal.

 If cube map texturing is enabled at the time a primitive is
 rasterized and if the set of six targets are not "cube complete",
 then it is as if texture mapping were disabled.  The targets of
 a cube map texture are "cube complete" if the array 0 of all six
 targets have identical, positive, and square dimensions, the array
 0 of all six targets were specified with the same internalformat,
 and the array 0 of all six targets have the same border width."

 After the 14th paragraph (page 116) add:

 "In a similiar fashion, the maximum allowable width and height
 (they must be the same) of a cube map texture must be at least
 2^(k-lod) for image arrays level 0 through k, where k is the
 log base 2 of MAX_CUBE_MAP_TEXTURE_SIZE_OES."

 Update the second paragraph (page 120) to say:

 ... "Currently, <target> must be
 TEXTURE_2D, TEXTURE_CUBE_MAP_POSITIVE_X_OES,
 TEXTURE_CUBE_MAP_NEGATIVE_X_OES, TEXTURE_CUBE_MAP_POSITIVE_Y_OES,
 TEXTURE_CUBE_MAP_NEGATIVE_Y_OES, TEXTURE_CUBE_MAP_POSITIVE_Z_OES,
 or TEXTURE_CUBE_MAP_NEGATIVE_Z_OES." ...

 Add after the second paragraph (page 120), the following:

 "When the target parameter to CopyTexImage2D is one of the six cube
 map 2D image targets, the error INVALID_VALUE is generated if the
 width and height parameters are not equal."

 Change paragraph one (page 124) to say:

 ... "<target> is the target, either TEXTURE_2D or TEXTURE_CUBE_MAP_OES."

 Add a final paragraph saying:

 "Texture parameters for a cube map texture apply to cube map
 as a whole; the six distinct 2D texture images use the
 texture parameters of the cube map itself.

 Change the first full paragraph on page 130 to:

 ... "If texturing is enabled for two-dimensional texturing but not cube map
 texturing (and TEXTURE_MIN_FILTER is one that requires a mipmap) at the
 time a primitive is rasterized and if the set of arrays
 TEXTURE_BASE_LEVEL through q = min{p,TEXTURE_MAX_LEVEL} is incomplete,
 based on the dimensions of array 0, then it is as if texture mapping were
 disabled."

 Follow the first full paragraph on page 130 with:

 "If cube map texturing is enabled and TEXTURE_MIN_FILTER is one that
 requires mipmap levels at the time a primitive is rasterized and
 if the set of six targets are not "mipmap cube complete", then it
 is as if texture mapping were disabled.  The targets of a cube map
 texture are "mipmap cube complete" if the six cube map targets are
 "cube complete" and the set of arrays TEXTURE_BASE_LEVEL through
 q are not incomplete (as described above)."

 Change the first sentence of the first paragraph (page 131) to say:

 "The state necessary for texture can be divided into two categories.
 First, there are the nine sets of mipmap arrays (one each for the
 one-, two-, and three-dimensional texture targets and six for the
 cube map texture targets) and their number." ...

 Change the second paragraph (page 132) to say:

 "In addition to the one-, two-, three-dimensional, and the six cube
 map sets of image arrays, the partially instantiated one-, two-,
 and three-dimensional and one cube map sets of proxy image arrays
 are maintained." ...

 Change the first sentence of the first paragraph (page 132) to say:

 "In addition to the default textures TEXTURE_2D and TEXTURE_CUBE_MAP_OES,
 named two-dimensional texture objects and cube map texture objects can be
 created and operated on." ...

 Change the second paragraph (page 132) to say:

 "A texture object is created by binding an unused name to
 TEXTURE_2D or TEXTURE_CUBE_MAP_OES." ...
 "If the new texture object is bound to TEXTURE_2D or TEXTURE_CUBE_MAP_OES,
 it remains a two-dimensional or cube map texture until it is deleted."

 Change the third paragraph (page 133) to say:

 "BindTexture may also be used to bind an existing texture object to
 either TEXTURE_2D or TEXTURE_CUBE_MAP_OES."

 Change paragraph five (page 133) to say:

 "In the initial state, TEXTURE_2D and TEXTURE_CUBE_MAP_OES have two-
 dimensional and cube map state vectors associated with them respectively."
 ...  "The initial two-dimensional and cube map texture is therefore
 operated upon, queried, and applied as TEXTUER_2D and TEXTURE_CUBE_MAP_OES
 respectively while 0 is bound to the corresponding targets."

 Change paragraph six (page 133) to say:

 ... "If a texture that is currently bound to one of the targets TEXTURE_2D
 or TEXTURE_CUBE_MAP_OES is deleted, it is as though BindTexture has been
 executed with the same <target> and <texture> zero." ...

 Replace the beginning sentences of the first paragraph (page 138)
 with:

 "Texturing is enabled or disabled using the generic Enable
 and Disable commands, respectively, with the symbolic constants
 TEXTURE_2D or TEXTURE_CUBE_MAP_OES to enable the two-dimensional or cube
 map texturing respectively.  If the cube map texture and the two-
 dimensional texture are enabled, then cube map texturing is used.  If
 texturing is disabled, a rasterized fragment is passed on unaltered to the
 next stage of the GL (although its texture coordinates may be discarded).
 Otherwise, a texture value is found according to the parameter values of
 the currently bound texture image of the appropriate dimensionality.

 However, when cube map texturing is enabled, the rules are
 more complicated.  For cube map texturing, the (s,t,r) texture
 coordinates are treated as a direction vector (rx,ry,rz) emanating
 from the center of a cube.  (The q coordinate can be ignored since
 it merely scales the vector without affecting the direction.) At
 texture application time, the interpolated per-fragment (s,t,r)
 selects one of the cube map face's 2D image based on the largest
 magnitude coordinate direction (the major axis direction).  If two
 or more coordinates have the identical magnitude, the implementation
 may define the rule to disambiguate this situation.  The rule must
 be deterministic and depend only on (rx,ry,rz).  The target column
 in the table below explains how the major axis direction maps to
 the 2D image of a particular cube map target.

  major axis
  direction     target                             sc     tc    ma
  ----------    -------------------------------    ---    ---   ---
   +rx          TEXTURE_CUBE_MAP_POSITIVE_X_OES    -rz    -ry   rx
   -rx          TEXTURE_CUBE_MAP_NEGATIVE_X_OES    +rz    -ry   rx
   +ry          TEXTURE_CUBE_MAP_POSITIVE_Y_OES    +rx    +rz   ry
   -ry          TEXTURE_CUBE_MAP_NEGATIVE_Y_OES    +rx    -rz   ry
   +rz          TEXTURE_CUBE_MAP_POSITIVE_Z_OES    +rx    -ry   rz
   -rz          TEXTURE_CUBE_MAP_NEGATIVE_Z_OES    -rx    -ry   rz

 Using the sc, tc, and ma determined by the major axis direction as
 specified in the table above, an updated (s,t) is calculated as
 follows

    s   =   ( sc/|ma| + 1 ) / 2
    t   =   ( tc/|ma| + 1 ) / 2

 This new (s,t) is used to find a texture value in the determined
 face's 2D texture image using the rules given in sections 3.8.5
 and 3.8.6." ...

 None

 Change the fourth paragraph (page 183) to say:

 "The GetTexParameter parameter <target> may be one of TEXTURE_2D,
 or TEXTURE_CUBE_MAP_OES, indicating the currently bound two-dimensional
 or cube map texture object."

 None

 INVALID_VALUE is generated when the target parameter to TexImage2D
 or CopyTexImage2D is one of the six cube map 2D image targets and
 the width and height parameters are not equal.