NV_texture_border_clamp

GL_NV_texture_border_clamp

 Jussi Rasanen, NVIDIA
 Greg Roth, NVIDIA

Greg Roth, NVIDIA (groth 'at' nvidia 'dot' com)

Complete

Date: Aug 24, 2012
Revision: 2

OpenGL ES Extension #149

OpenGL ES 2.0 is required.

This extension is written against the OpenGL ES 2.0.25
specification.

OES_texture_3D affects the definition of this extension.

OpenGL ES provides only a single clamping wrap mode: CLAMP_TO_EDGE.
However, the ability to clamp to a constant border color can be
useful to quickly detect texture coordinates that exceed their
expected limits or to dummy out any such accesses with transparency
or a neutral color in tiling or light maps.

This extension defines an additional texture clamping algorithm.
CLAMP_TO_BORDER_NV clamps texture coordinates at all mipmap levels
such that NEAREST and LINEAR filters of clamped coordinates return
only the constant border color. This does not add the ability for
textures to specify borders using glTexImage2D, but only to clamp
to a constant border value set using glTexParameter.

None.

Accepted by the <pname> parameter of TexParameteri, TexParameterf,
TexParameteriv, and TexParameterfv:

    TEXTURE_BORDER_COLOR_NV                         0x1004

Accepted by the <param> parameter of TexParameteri and
TexParameterf, and by the <params> parameter of TexParameteriv and
TexParameterfv, and returned by the <params> parameter of
GetTexParameteriv and GetTexParameterfv when their <pname> parameter
is TEXTURE_WRAP_S, TEXTURE_WRAP_T, or TEXTURE_WRAP_R_OES:

    CLAMP_TO_BORDER_NV                              0x812D

Modify Section 3.7.4 "Texture Parameters"

Append to the end of the first paragraph:

If the values for TEXTURE_BORDER_COLOR_NV are specified as integers,
they are converted to floating-point as described in section 2.1.2.
Each of the four values set by TEXTURE_BORDER_COLOR_NV is clamped to
lie in [0, 1].

Modify Table 3.10, edit the following lines:

Name                    Type      Legal Values
==============          =======   ====================
TEXTURE_WRAP_S          integer   CLAMP_TO_EDGE, REPEAT, MIRRORED_REPEAT,
                                  CLAMP_TO_BORDER_NV
TEXTURE_WRAP_T          integer   CLAMP_TO_EDGE, REPEAT, MIRRORED_REPEAT,
                                  CLAMP_TO_BORDER_NV
TEXTURE_WRAP_R_OES      integer   CLAMP_TO_EDGE, REPEAT, MIRRORED_REPEAT,
                                  CLAMP_TO_BORDER_NV

and add:

Name                    Type      Legal Values
==============          =======   ====================
TEXTURE_BORDER_COLOR_NV 4 floats  any 4 values in {0,1}

Modify Section 3.7.6 "Texture Wrap Modes"

Add after wrap mode CLAMP_TO_EDGE:

Wrap Mode CLAMP_TO_BORDER_NV

CLAMP_TO_BORDER_NV clamps texture coordinates at all mipmaps such
that the texture filter always samples the constant border color for
fragments whose corresponding texture coordinate is sufficiently far
outside the range [0, 1].  The color returned when clamping is
derived only from the constant border color.

Texture coordinates are clamped to the range [min, max]. The minimum
value is defined as

    min = -1 / 2N

where N is the size of the one-, two-, or three-dimensional texture
image in the direction of clamping.  The maximum value is defined as

    max = 1 - min

so that clamping is always symmetric about the [0,1] mapped range of
a texture coordinate.

Modify Section 3.7.7 "Texture Minification"

Add to the end of Subsection "Scale Factor and Level of Detail"

If any of the selected Tijk or Tij in the above equations refer to a
border texel with i < 0, j < 0, k < 0, i >= ws, j >= hs, or k >= ds,
then the border values defined by TEXTURE_BORDER_COLOR_NV are used
instead of the unspecified value or values. If the texture contains
color components, the values of TEXTURE_BORDER_COLOR_NV are
interpreted as an RGBA color to match the texture's internal format
in a manner consistent with table 3.8. If the texture contains depth
components, the first component of TEXTURE_BORDER_COLOR_NV is
interpreted as a depth value.

Modify Section 3.7.12 "Texture state"

Modify the last two sentences of the section:

Next, there are the two sets of texture properties; each consists
of the selected minification and magnification filters, the wrap
modes for s, t, and r, and the TEXTURE_BORDER_COLOR_NV. In the
initial state, the value assigned to TEXTURE_MIN_FILTER is NEAREST_-
MIPMAP_LINEAR, and the value for TEXTURE_MAG_FILTER is LINEAR. s, t,
and r wrap modes are all set to REPEAT, and TEXTURE_BORDER_COLOR_NV
is (0,0,0,0).

None.

Modify table 6.8:

Change the type information changes for these parameters.
                                                            Initial
Get Value                 Type   Get Command      Value   Description    Sec.
---------                 ------ -----------      ------- -----------    ----
TEXTURE_WRAP_S            n x Z4 GetTexParameter  REPEAT  Texture wrap   3.7
TEXTURE_WRAP_T            n x Z4 GetTexParameter  REPEAT  Texture wrap   3.7
TEXTURE_WRAP_R_OES        n x Z4 GetTexParameter  REPEAT  Texture wrap   3.7

Add the following parameter:

Get Value                 Type   Get Command      Value   Description    Sec.
---------                 ------ -----------      ------- -----------    ----
TEXTURE_BORDER_COLOR_NV   2+ x C GetTexParameter  0,0,0,0 Texture border 3.7

If OES_texture_3D is not supported, ignore all references to
three-dimensional textures and token TEXTURE_WRAP_R_OES as well
as any reference to r wrap modes.  References to Tijk, k, and ds in
section 3.7.6 should also be removed.

None

Rev.    Date       Author       Changes
----   --------    ---------    -------------------------------------
 4     04 Sep 2012 groth        Restored langauge in 3.7.7 about texture borders
 3     29 Aug 2012 groth        Minor copy edits.
 2     24 Aug 2012 groth        Clarified constant color language and tex_3d dependency
 1     14 Aug 2012 groth        Initial draft based off ARB_texture_border_clamp