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GL_EXT_texture3D
EXT_texture3D
Name Strings
GL_EXT_texture3D
Version
$Date: 1996/04/05 19:17:05 $ $Revision: 1.22 $
Number
6
Dependencies
EXT_abgr affects the definition of this extension
EXT_texture is required
Overview
This extension defines 3-dimensional texture mapping. In order to
define a 3D texture image conveniently, this extension also defines the
in-memory formats for 3D images, and adds pixel storage modes to support
them.
One important application of 3D textures is rendering volumes of image
data.
void TexImage3DEXT(enum target,
int level,
enum internalformat,
sizei width,
sizei height,
sizei depth,
int border,
enum format,
enum type,
const void* pixels);
Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev, and by the <pname> parameter of PixelStore:
PACK_SKIP_IMAGES_EXT 0x806B
PACK_IMAGE_HEIGHT_EXT 0x806C
UNPACK_SKIP_IMAGES_EXT 0x806D
UNPACK_IMAGE_HEIGHT_EXT 0x806E
Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, by
the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, and
GetDoublev, and by the <target> parameter of TexImage3DEXT, GetTexImage,
GetTexLevelParameteriv, GetTexLevelParameterfv, GetTexParameteriv, and
GetTexParameterfv:
TEXTURE_3D_EXT 0x806F
Accepted by the <target> parameter of TexImage3DEXT,
GetTexLevelParameteriv, and GetTexLevelParameterfv:
PROXY_TEXTURE_3D_EXT 0x8070
Accepted by the <pname> parameter of GetTexLevelParameteriv and
GetTexLevelParameterfv:
TEXTURE_DEPTH_EXT 0x8071
Accepted by the <pname> parameter of TexParameteriv, TexParameterfv,
GetTexParameteriv, and GetTexParameterfv:
TEXTURE_WRAP_R_EXT 0x8072
Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
GetFloatv, and GetDoublev:
MAX_3D_TEXTURE_SIZE_EXT 0x8073
Additions to Chapter 2 of the GL Specification (OpenGL Operation)
None
Additions to Chapter 3 of the GL Specification (Rasterization)
The pixel storage modes are augmented to support 3D image formats in
memory. Table 3.1 is replaced with the table below:
Parameter Name Type Initial Value Valid Range
-------------- ---- ------------- -----------
UNPACK_SWAP_BYTES boolean FALSE TRUE/FALSE
UNPACK_LSB_FIRST boolean FALSE TRUE/FALSE
UNPACK_ROW_LENGTH integer 0 [0, infinity]
UNPACK_SKIP_ROWS integer 0 [0, infinity]
UNPACK_SKIP_PIXELS integer 0 [0, infinity]
UNPACK_ALIGNMENT integer 4 1, 2, 4, 8
UNPACK_IMAGE_HEIGHT_EXT integer 0 [0, infinity]
UNPACK_SKIP_IMAGES_EXT integer 0 [0, infinity]
Table 3.1: PixelStore parameters pertaining to one or more of
DrawPixels, TexImage1D, TexImage2D, and TexImage3DEXT.
When TexImage3DEXT is called, the groups in memory are treated as being
arranged in a sequence of adjacent rectangles. Each rectangle is a
2-dimensional image, whose size and organization are specified by the
<width> and <height> parameters to TexImage3DEXT. The values of
UNPACK_ROW_LENGTH and UNPACK_ALIGNMENT control the row-to-row spacing in
these images in exactly the manner described in the GL Specification for
2-dimensional images. If the value of UNPACK_IMAGE_HEIGHT_EXT is not
positive, then the number of rows in each 2-dimensional image is
<height>; otherwise the number of rows is UNPACK_IMAGE_HEIGHT_EXT. Each
2-dimensional image comprises an integral number of rows, and is exactly
adjacent to its neighbor images.
The mechanism for selecting a sub-volume of a 3-dimensional image builds
on the mechanism for selecting a sub-rectangle of groups from a larger
containing rectangle. If UNPACK_SKIP_IMAGES_EXT is positive, the
pointer is advanced by UNPACK_SKIP_IMAGES_EXT times the number of
elements in one 2-dimensional image. Then <depth> 2-dimensional images
are processed, each having a subimage extracted in the manner described
in the GL Specification for 2-dimensional images.
The selected groups are processed as though they were part of a
2-dimensional image. When the final R, G, B, and A components have been
computed for a group, they are assigned to components of a texel as
described by Table 3.6 in the EXT_texture extension. Counting from
zero, each resulting Nth texel is assigned internal integer coordinates
[i,j,k], where
i = (N mod width) - border
j = ((N div width) mod height) - border
k = ((N div (width * height)) mod depth) - border
and the div operator performs integer division with truncation. Thus
the last 2-dimensional image of the 3-dimensional image is indexed with
the highest value of k. The dimensions of the 3-dimensional texture
image are <width> x <height> x <depth>. Integer values that will
represent the base-2 logarithm of these dimensions are n, m, and l,
defined such that
width = 2**n + (2 * border)
height = 2**m + (2 * border)
depth = 2**l + (2 * border)
It is acceptable for an implementation to vary its allocation of
internal component resolution based any TexImage3DEXT parameter, but the
allocation must not be a function of any other factor, and cannot be
changed once it is established. In particular, allocations must be
invariant -- the same allocation must be made each time a texture image
is specified with the same parameter values. Provision is made for an
application to determine what component resolutions are available
without having to fully specify the texture (see below).
Texture Wrap Modes
------------------
The additional token value TEXTURE_WRAP_R_EXT is accepted by
TexParameteri, TexParameterv, TexParameteriv, and TexParameterfv,
causing table 3.7 to be replaced with the table below:
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
TEXTURE_MAG_FILTER integer NEAREST, LINEAR
TEXTURE_BORDER_COLOR 4 floats any 4 values in [0,1]
Table 3.7: Texture parameters and their values.
If TEXTURE_WRAP_R_EXT is set to REPEAT, then the GL ignores the integer
part of R coordinates, using only the fractional part. CLAMP causes R
to be clamped to the range [0, 1]. The initial state is for
TEXTURE_WRAP_R_EXT to be REPEAT.
Texture Minification
--------------------
Continuous coordinates s, t, u, and v are defined in figure 3.10 of the
GL Specification. To discuss 3-dimensional texture mapping, coordinates
r and w are defined similarly. Coordinate w is equal to -border at the
"far" edge of the 3D image, understanding the image to be right-handed,
with k values increasing toward the viewer. It has value depth+border
at the near edge of this volume. Coordinate r has the same direction,
but is normalized so that it is 0.0 and 1.0 at the "far" and "near"
edges of a borderless volume. If the volume has a border, the 0.0 and
1.0 mappings of r continue to bound the core image.
The formulas for p, used to determine the level of detail, are modified
by including dw/dx and dw/dy terms in the obvious ways. Equation 3.7
sums (dw/dx)**2 into the left term, and (dw/dy)**2 into the right term.
Equation 3.8 has ((dw/dx * Dx + dw/dy * Dy)**2 added to the two terms
under the square root. The requirements for the function f(x,y) become
1. f(x, y) is continuous and monotonically increasing in each of
|du/dx|, |du/dy|, |dv/dx|, |dv/dy|, |dw/dx|, and |dw/dy|.
2. Let
m_u = max(|du/dx|, |du/dy|)
m_v = max(|dv/dx|, |dv/dy|)
m_w = max(|dw/dx|, |dw/dy|)
Then
max(m_u, m_v, m_w) <= f(x, y) <= m_u + m_v + m_w
The i and j coordinates of the texel selected for NEAREST filtering are
as defined in equations 3.9 and 3.10 of the GL Specification.
Coordinate k is computed as
/ floor(w), r < 1
k = (
\ 2**l - 1, r = 1
A 2x2x2 cube of texels is selected for LINEAR filtering. The i and j
coordinates of these texels are computed as defined in the GL
Specification for 2-dimensional images. The k coordinates are
computed as
/ floor(w - 1/2) mod 2**l, TEXTURE_WRAP_R_EXT is REPEAT
k0 = (
\ floor(w - 1/2), TEXTURE_WRAP_R_EXT is CLAMP
/ (k0 + 1) mod 2**l, TEXTURE_WRAP_R_EXT is REPEAT
k1 = (
\ k0 + 1, TEXTURE_WRAP_R_EXT is CLAMP
Let
A = frac(u - 1/2)
B = frac(v - 1/2)
C = frac(w - 1/2)
where frac(x) denotes the fractional part of x. Let T[i,j,k] be the
texel at location [i,j,k] in the texture image. Then the texture value,
T, is found as
T = (1-A) * (1-B) * (1-C) * T[i0,j0,k0] +
A * (1-B) * (1-C) * T[i1,j0,k0] +
(1-A) * B * (1-C) * T[i0,j1,k0] +
A * B * (1-C) * T[i1,j1,k0] +
(1-A) * (1-B) * C * T[i0,j0,k1] +
A * (1-B) * C * T[i1,j0,k1] +
(1-A) * B * C * T[i0,j1,k1] +
A * B * C * T[i1,j1,k1]
for a 3-dimensional texture. If any of the selected T[i,j,k] in the
above equation refer to a border texel with unspecified value, then the
border color given by the current setting of TEXTURE_BORDER_COLOR is
used instead of the unspecified value or values.
Mipmapping
----------
TEXTURE_MIN_FILTER values NEAREST_MIPMAP_NEAREST, NEAREST_MIPMAP_LINEAR,
LINEAR_MIPMAP_NEAREST, and LINEAR_MIPMAP_LINEAR each require the use of
a mipmap. A 3-dimensional mipmap is an ordered set of arrays
representing the same image; each array has a resolution lower than the
previous one. If the texture, excluding is border, has dimensions
2**n x 2**m x 2**l, then there are exactly max(n, m, l) + 1 mipmap
arrays. Each subsequent array has dimensions
size(i-1) x size(j-1) x size(k-1)
where the dimensions of the previous array are
size(i) x size(j) x size(k)
and
/ 2**x + 2*border, x > 0
size(x) = (
\ 1 + 2*border, x <= 0
Each array in a 3-dimensional mipmap is transmitted to the GL using
TexImage3DEXT; the array being set is indicated with the <level>
parameter. The rules for completeness of the set of arrays are as
described in the GL Specification, augmented in EXT_texture. The rules
for mipmap array selection, and for filtering of the two selected
arrays, are also as described in the GL Specification. Finally, the
rules for texture magnification are also exactly as described in the
GL Specification.
Texture Application
-------------------
3-dimensional texture mapping is enabled and disabled using the generic
Enable and Disable commands, with <cap> specified as TEXTURE_3D_EXT. If
either or both TEXTURE_1D or TEXTURE_2D are enabled at the same time as
TEXTURE_3D_EXT, the 3-dimensional texture is used.
Query support
-------------
The proxy texture PROXY_TEXTURE_3D_EXT can be used by applications to
query an implementations maximum configurations just as it can be for
1-dimensional and 2-dimensional textures.
Alternate sets of partial per-level texture state are defined for
the proxy texture PROXY_TEXTURE_3D_EXT. Specifically,
TEXTURE_WIDTH, TEXTURE_HEIGHT, TEXTURE_DEPTH_EXT, TEXTURE_BORDER,
TEXTURE_COMPONENTS, TEXTURE_RED_SIZE_EXT, TEXTURE_GREEN_SIZE_EXT,
TEXTURE_BLUE_SIZE_EXT, TEXTURE_ALPHA_SIZE_EXT,
TEXTURE_LUMINANCE_SIZE_EXT, and TEXTURE_INTENSITY_SIZE_EXT are
maintained the the proxy texture. When TexImage3DEXT is called
with <target> set to PROXY_TEXTURE_3D_EXT, these proxy state
values are always respecified, even if the texture is too large to
actually be used. If the texture is too large, all of these state
variables are set to zero. If the texture could be accommodated
by TexImage3DEXT called with <target> TEXTURE_3D_EXT, these values
are set as though TEXTURE_3D_EXT were being defined. All of these
state value can be queried with GetTexLevelParameteriv with
<target> set to PROXY_TEXTURE_3D_EXT. Calling TexImage3DEXT with
<target> PROXY_TEXTURE_3D_EXT has no effect on the actual
3-dimensional texture or its state.
There is no image associated with PROXY_TEXTURE_3D_EXT. Therefore
PROXY_TEXTURE_3D_EXT cannot be used as a texture, and its image must
never be queried using GetTexImage. (The error INVALID_ENUM results if
this is attempted.) Likewise, there is no nonlevel-related state
associated with a proxy texture, so calling GetTexParameteriv or
GetTexParameterfv with <target> PROXY_TEXTURE_3D_EXT results in the
error INVALID_ENUM.
Additions to Chapter 4 of the GL Specification (Per-Fragment Operations
and the Framebuffer)
None
Additions to Chapter 5 of the GL Specification (Special Functions)
TexImage3DEXT with a proxy target is not included in display
lists, but is instead executed immediately.
Additions to Chapter 6 of the GL Specification (State and State Requests)
3-dimensional texture images are queried using GetTexImage with its
<target> parameter set to TEXTURE_3D_EXT. The assignment of texel
component values to the initial R, G, B, and A components of a pixel
group is described in EXT_texture. Pixel transfer and pixel storage
operations are applied as if the image were 2-dimensional, except that
the additional pixel storage state values PACK_IMAGE_HEIGHT_EXT and
PACK_SKIP_IMAGES_EXT affect the storage of the image into memory. The
correspondence of texels to memory locations is as defined for
TexImage3DEXT above, substituting PACK* state for UNPACK* state in all
occurrences.
Additions to the GLX Specification
None
GLX Protocol
A new GL rendering command is added. This command contains pixel data;
thus it is sent to the server either as part of a glXRender request
or as part of a glXRenderLarge request:
TexImage3DEXT
2 84+n+p rendering command length
2 4114 rendering command opcode
1 BOOL swap_bytes
1 BOOL lsb_first
2 unused
4 CARD32 row_length
4 CARD32 image_height
4 CARD32 image_depth
4 CARD32 skip_rows
4 CARD32 skip_images
4 CARD32 skip_volumes
4 CARD32 skip_pixels
4 CARD32 alignment
4 ENUM target
4 INT32 level
4 ENUM internalformat
4 INT32 width
4 INT32 height
4 INT32 depth
4 INT32 size4d
4 INT32 border
4 ENUM format
4 ENUM type
4 CARD32 null_image
n LISTofBYTE pixels
p unused, p=pad(n)
If the command is encoded in a glXRenderLarge request, the command
opcode and command length fields above are expanded to 4 bytes each:
4 88+n+p rendering command length
4 4114 rendering command opcode
If <width> < 0, <height> < 0, <depth> < 0, <format> is invalid or <type> is
invalid, then the command is erroneous and n=0.
<pixels> is arranged as a sequence of adjacent rectangles. Each rectangle is a
2-dimensional image, whose structure is determined by the image height and the
parameters <swap_bytes>, <lsb_first>, <row_length>, <skip_rows>, <skip_pixels>,
<alignment>, <width>, <format>, and <type> given in the request. If <image_height>
is not positive then the number of rows (i.e., the image height) is <height>;
otherwise the number of rows is <image_height>.
<skip_images> allows a sub-volume of the 3-dimensional image to be selected.
If <skip_images> is positive, then the pointer is advanced by <skip_images>
times the number of elements in one 2-dimensional image. Then <depth>
2-dimensional images are read, each having a subimage extracted in the
manner described in Appendix A of the GLX Protocol Specification.
Dependencies on EXT_abgr
If EXT_abgr is supported, the <format> parameter of TexImage3DEXT
accepts ABGR_EXT. Otherwise it does not.
Dependencies on EXT_texture
EXT_texture is required. All of the <components> tokens defined by
EXT_texture are accepted by the <internalformat> parameter of
TexImage3DEXT, with the same semantics that are defined by EXT_texture.
The query and error extensions defined by EXT_texture are extended in
this document.
Errors
INVALID_ENUM is generated if <target> is not TEXTURE_3D_EXT or
PROXY_TEXTURE_3D_EXT.
INVALID_ENUM is generated if the <target> parameter to
GetTexParameteriv, GetTexParameterfv or GetTexImage is
PROXY_TEXTURE_3D_EXT.
INVALID_VALUE is generated if <level> is less than zero
INVALID_ENUM is generated if <internalformat> is not ALPHA, RGB, RGBA,
LUMINANCE, LUMINANCE_ALPHA, or one of the tokens defined by the
EXT_texture extension. (Values 1, 2, 3, and 4 are not accepted as
internal formats by TexImage3DEXT).
INVALID_VALUE is generated if <width>, <height>, or <depth> is less than
zero, or cannot be represented as 2**k + 2*border for some integer k.
INVALID_VALUE is generated if <border> is not 0 or 1.
INVALID_ENUM is generated if <format> is not COLOR_INDEX, RED, GREEN,
BLUE, ALPHA, RGB, RGBA, LUMINANCE, or LUMINANCE_ALPHA (or ABGR_EXT if
EXT_abgr is supported).
INVALID_ENUM is generated if <type> is not UNSIGNED_BYTE, BYTE,
UNSIGNED_SHORT, SHORT, UNSIGNED_INT, INT, or FLOAT.
INVALID_OPERATION is generated if TexImage3DEXT is called between
execution of Begin and the corresponding execution of End.
TEXTURE_TOO_LARGE_EXT is generated if the texture as specified cannot be
accommodated by the implementation. This error will not occur if none
of <width>, <height>, or <depth> is greater than MAX_3D_TEXTURE_SIZE_EXT.
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
UNPACK_SKIP_IMAGES_EXT GetIntegerv Z+ 0 -
UNPACK_IMAGE_HEIGHT_EXT GetIntegerv Z+ 0 -
PACK_SKIP_IMAGES_EXT GetIntegerv Z+ 0 -
PACK_IMAGE_HEIGHT_EXT GetIntegerv Z+ 0 -
TEXTURE_3D_EXT IsEnabled B FALSE texture/enable
TEXTURE_WRAP_R_EXT GetTexParameteriv 1 x Z2 REPEAT texture
TEXTURE_DEPTH_EXT GetTexLevelParameteriv 1 x 2 x levels x Z+ 0 -
(old state with new type information)
TEXTURE GetTexImage 3 x 1 x levels x I null -
TEXTURE_RED_SIZE_EXT GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_GREEN_SIZE_EXT GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_BLUE_SIZE_EXT GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_ALPHA_SIZE_EXT GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_LUMINANCE_SIZE_EXT GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_INTENSITY_SIZE_EXT GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_WIDTH GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_HEIGHT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 -
TEXTURE_BORDER GetTexLevelParameteriv 3 x 2 x levels x Z+ 0 -
TEXTURE_COMPONENTS (1D and 2D) GetTexLevelParameteriv 2 x 2 x levels x Z42 1 -
TEXTURE_COMPONENTS (3D) GetTexLevelParameteriv 1 x 2 x levels x Z38 LUMINANCE -
TEXTURE_BORDER_COLOR GetTexParameteriv 3 x C 0, 0, 0, 0 texture
TEXTURE_MIN_FILTER GetTexParameteriv 3 x Z6 NEAREST_MIPMAP_LINEAR texture
TEXTURE_MAG_FILTER GetTexParameteriv 3 x Z2 LINEAR texture
TEXTURE_WRAP_S GetTexParameteriv 3 x Z2 REPEAT texture
TEXTURE_WRAP_T GetTexParameteriv 2 x Z2 REPEAT texture
New Implementation Dependent State
Get Value Get Command Type Minimum Value
--------- ----------- ---- -------------
MAX_3D_TEXTURE_SIZE_EXT GetIntegerv Z+ 16
Implementation Support
List of OpenGL implementations supporting the GL_EXT_texture3D extension
Original File
Original text file for the GL_EXT_texture3D extension
Page generated on Sun Nov 20 18:37:23 2005