## NVIDIA DRIVE OS Linux API Reference

#### 5.1.6.1 Release For Test and Development only

GL_EXT_sparse_texture
Name

EXT_sparse_texture

Name Strings

GL_EXT_sparse_texture

Contributors

Dominik Witczak, Mobica
Contributors to ARB_sparse_texture

Xi Chen, NVIDIA

Contact

Daniel Koch, NVIDIA Corporation (dkoch 'at' nvidia.com)

Notice

Copyright (c) 2013 The Khronos Group Inc. Copyright terms at

Portions Copyright (c) 2014 NVIDIA Corporation.

Status

Complete.

Version

Revision:                   3

Number

OpenGL ES Extension #240

Dependencies

OpenGL ES 3.1 is required.

This extension is written against the OpenGL ES 3.1 (June 4, 2014)
Specification.

This extension interacts with OES_texture_border_clamp.

This extension interacts with EXT_texture_border_clamp.

This extension interacts with OES_texture_cube_map_array.

This extension interacts with EXT_texture_cube_map_array.

This extension interacts with OES_texture_view.

This extension interacts with EXT_texture_view.

This extension interacts with EXT_texture_norm16.

The definition of this extension is affected by the presence of
EXT_direct_state_access.

Overview

Recent advances in application complexity and a desire for higher
resolutions have pushed texture sizes up considerably. Often, the amount
of physical memory available to a graphics processor is a limiting factor
in the performance of texture-heavy applications. Once the available
physical memory is exhausted, paging may occur bringing performance down
considerably - or worse, the application may fail. Nevertheless, the amount
of address space available to the graphics processor has increased to the
point where many gigabytes - or even terabytes of address space may be
usable even though that amount of physical memory is not present.

This extension allows the separation of the graphics processor's address
space (reservation) from the requirement that all textures must be
physically backed (commitment). This exposes a limited form of
virtualization for textures. Use cases include sparse (or partially
resident) textures, texture paging, on-demand and delayed loading of
texture assets and application controlled level of detail.

New Procedures and Functions

void TexPageCommitmentEXT(enum target,
int level,
int xoffset,
int yoffset,
int zoffset,
sizei width,
sizei height,
sizei depth,
boolean commit);

[[ The following is only added if EXT_direct_state_access is supported. ]]

void TexturePageCommitmentEXT(uint texture,
int level,
int xoffset,
int yoffset,
int zoffset,
sizei width,
sizei height,
sizei depth,
boolean commit);

New Tokens

Accepted by the <pname> parameter to TexParameter{if}{v},
GetTexParameter{if}v, TexParameterI{u}ivOES, GetTexParameterI{u}ivOES
TexParameterI{u}ivEXT, and GetTexParameterI{u}ivEXT:

TEXTURE_SPARSE_EXT                          0x91A6
VIRTUAL_PAGE_SIZE_INDEX_EXT                 0x91A7

Accepted by the <pname> parameter of GetTexParameter{if}v,
GetTexParameterIi{u}vOES, and GetTexParameterIi{u}vEXT:

NUM_SPARSE_LEVELS_EXT                       0x91AA

Accepted by the <pname> parameter to GetInternalformativ:

NUM_VIRTUAL_PAGE_SIZES_EXT                  0x91A8

VIRTUAL_PAGE_SIZE_X_EXT                     0x9195
VIRTUAL_PAGE_SIZE_Y_EXT                     0x9196
VIRTUAL_PAGE_SIZE_Z_EXT                     0x9197

Accepted by the <target> parameter to GetInternalformativ:

TEXTURE_2D                                  0x0DE1
TEXTURE_2D_ARRAY                            0x8C1A
TEXTURE_CUBE_MAP                            0x8513
TEXTURE_CUBE_MAP_ARRAY_OES                  0x9009
TEXTURE_3D                                  0x806F

Accepted by the <pname> parameter to GetIntegerv, GetFloatv,
GetInteger64v, and GetBooleanv:

MAX_SPARSE_TEXTURE_SIZE_EXT                 0x9198
MAX_SPARSE_3D_TEXTURE_SIZE_EXT              0x9199
MAX_SPARSE_ARRAY_TEXTURE_LAYERS_EXT         0x919A
SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_EXT  0x91A9

Additions to Chapter 8 of the OpenGL ES 3.1 Specification (Textures and
Samplers)

Add the "Supports Sparse Allocation" column to Table 8.13, "Correspondence
of sized internal color formats..."

+-------------------------------+-------------------------------+
| Sized Internal Format         | Supports Sparse Allocation    |
+-------------------------------+-------------------------------+
| R8                            | Y                             |
| R8_SNORM                      | Y                             |
| R16_EXT                       | Y                             |
| R16_SNORM_EXT                 | Y                             |
| RG8                           | Y                             |
| RG8_SNORM                     | Y                             |
| RG16_EXT                      | Y                             |
| RG16_SNORM_EXT                | Y                             |
| RGB565                        | Y                             |
| RGB8                          |                               |
| RGB8_SNORM                    |                               |
| RGB16_EXT                     |                               |
| RGB16_SNORM_EXT               |                               |
| RGBA4                         |                               |
| RGB5_A1                       |                               |
| RGBA8                         | Y                             |
| RGBA8_SNORM                   | Y                             |
| RGB10_A2                      | Y                             |
| RGB10_A2UI                    | Y                             |
| RGBA16_EXT                    | Y                             |
| RGBA16_SNORM_EXT              | Y                             |
| SRGB8                         |                               |
| SRGB8_ALPHA8                  |                               |
| R16F                          | Y                             |
| RG16F                         | Y                             |
| RGB16F                        |                               |
| RGBA16F                       | Y                             |
| R32F                          | Y                             |
| RG32F                         | Y                             |
| RGB32F                        |                               |
| RGBA32F                       | Y                             |
| R11F_G11F_B10F                | Y                             |
| RGB9_E5                       | Y                             |
| R8I                           | Y                             |
| R8UI                          | Y                             |
| R16I                          | Y                             |
| R16UI                         | Y                             |
| R32I                          | Y                             |
| R32UI                         | Y                             |
| RG8I                          | Y                             |
| RG8UI                         | Y                             |
| RG16I                         | Y                             |
| RG16UI                        | Y                             |
| RG32I                         | Y                             |
| RG32UI                        | Y                             |
| RGB8I                         |                               |
| RGB8UI                        |                               |
| RGB16I                        |                               |
| RGB16UI                       |                               |
| RGB32I                        |                               |
| RGB32UI                       |                               |
| RGBA8I                        | Y                             |
| RGBA8UI                       | Y                             |
| RGBA16I                       | Y                             |
| RGBA16UI                      | Y                             |
| RGBA32I                       | Y                             |
| RGBA32UI                      | Y                             |
+-------------------------------+-------------------------------+

Insert the following paragraph before Table 8.16:

If <pname> is TEXTURE_SPARSE_EXT or VIRTUAL_PAGE_SIZE_INDEX_EXT, then
the state is stored in the texture, but only takes effect the next time
storage is allocated for a texture using TexStorage*. If the value of
TEXTURE_IMMUTABLE_FORMAT is TRUE, then TEXTURE_SPARSE_EXT and
VIRTUAL_PAGE_SIZE_INDEX_EXT cannot be changed and an error is generated.

Append to Table 8.20: "Texture parameters and their values."

+------------------------------+---------+---------------------------+
| Name                         | Type    | Legal values              |
+------------------------------+---------+---------------------------+
| TEXTURE_SPARSE_EXT           | boolean | TRUE, FALSE               |
| VIRTUAL_PAGE_SIZE_INDEX_EXT  | int     | any non-negative integer  |
+------------------------------+---------+---------------------------+

Add to the Errors table for TexParameter*

INVALID_OPERATION is generated if <pname> is TEXTURE_SPARSE_EXT or
VIRTUAL_PAGE_SIZE_INDEX_EXT and the value of TEXTURE_IMMUTABLE_FORMAT for
the texture identified by <target> is TRUE.

INVALID_VALUE is generated if <pname> is TEXTURE_SPARSE_EXT, <pname>
is TRUE and <target> is not one of TEXTURE_2D, TEXTURE_2D_ARRAY,
TEXTURE_CUBE_MAP, TEXTURE_CUBE_MAP_ARRAY_OES, or TEXTURE_3D.

Additions to Section 8.16view (Texture Views), of the OpenGL ES
Specification (as added by OES_texture_view or EXT_texture_view):

Texture views may be created that reference sparse textures (see
Section 8.17sparse.1), and in such cases, the view is considered to be sparse.
Should a texture view reference part or all of the tail of a sparse
texture, then modifications to the commitment of that tail via the view
affect the tail of the parent texture and all other views that reference
the tail, even for portions of the tail outside the controlling view.

Additions to Section 8.17 of the OpenGL Specification, "Immutable-Format
Texture Images"

Add the following bullet point to the list of psuedo-operations performed
by all variants of TexStorage* (p.188):

* If TEXTURE_SPARSE_EXT is TRUE, only virtual address space is
allocated for the texture but physical backing store is not.
Physical store for pages of a virtual texture may be committed and
decommitted by calling TexPageCommitmentEXT. The page size chosen
for the texture is taken from the texture's value of
VIRTUAL_PAGE_SIZE_INDEX_EXT. In this case, <width>, <height> and
<depth> must either be integer multiples of the selected virtual
page size in the X, Y and Z dimensions, respectively, or be less
than those dimensions. Additionally, the dimensions of sparse
textures must be compatible with the chosen value of
<internalFormat> as described in Section 8.17sparse.1.

Add to the errors that may be generated by TexStorage*:

An INVALID_OPERATION error is generated if the texture's
TEXTURE_SPARSE_EXT parameter is TRUE and the value of its
VIRTUAL_PAGE_SIZE_INDEX_EXT parameter is greater than or equal to
NUM_VIRTUAL_PAGE_SIZES_EXT for the specified target and internal
format.

An INVALID_VALUE error is generated if the texture's TEXTURE_SPARSE_EXT
parameter is TRUE and any of the following are true:

* <target> is TEXTURE_3D, and <width>, <height>, or <depth>
is greater than MAX_SPARSE_3D_TEXTURE_SIZE_EXT;

* <target> is not TEXTURE_3D, and <width> or <height> is greater
than MAX_SPARSE_TEXTURE_SIZE_EXT; or

* <target> is TEXTURE_2D_ARRAY or TEXTURE_CUBE_MAP_ARRAY_OES and
<depth> is greater than MAX_SPARSE_TEXTURE_ARRAY_LAYERS_EXT.

An INVALID_VALUE error is generated if the texture's
TEXTURE_SPARSE_EXT parameter is TRUE and <width> or <height> is greater
than the value of MAX_SPARSE_3D_TEXTURE_SIZE_EXT when <target> is
TEXTURE_3D, or if <height> or <depth> is greater than the value of
MAX_SPARSE_ARRAY_TEXTURE_LAYERS_EXT if <target> is a 2D array
texture target, respectively.

An INVALID_VALUE error is generated if TEXTURE_SPARSE_EXT is TRUE and
<width>, <height> or <depth> is is not an integer multiple of the
page size in the corresponding dimension.

If the value of SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_EXT is FALSE,
then TexStorage* will generate an INVALID_OPERATION error if

* the texture's TEXTURE_SPARSE_EXT parameter is TRUE,

* <target> is one of TEXTURE_2D_ARRAY, TEXTURE_CUBE_MAP, or
TEXTURE_CUBE_MAP_ARRAY_OES, and

* for the virtual page size corresponding to the
VIRTUAL_PAGE_SIZE_INDEX_EXT parameter, either of the following is
true:

- <width> is not a multiple of VIRTUAL_PAGE_SIZE_X_EXT *
2^(<levels>-1), or

- <height> is not a multiple of VIRTUAL_PAGE_SIZE_Y_EXT *
2^(<levels>-1).

Insert Section 8.17sparse, "Sparse Textures and Commitment"
following section 8.17 "Immutable-Format Texture Images".

Textures may be allocated such that their images' physical backing
store is only partially allocated. Only immutable format textures may
be sparsely allocated. To allocate a sparse texture, set a texture's
TEXTURE_SPARSE_EXT parameter to TRUE before allocating storage for it
with TexStorage*.

Insert Subsection 8.17sparse.1, "Allocation of and Access to Sparse Textures"

Sparse textures are allocated setting a texture's TEXTURE_SPARSE_EXT
parameter to TRUE and then issuing one of the TexStorage* commands.
The dimensions of a sparse texture must be compatible with the internal
format chosen for the texture. Each internal format has zero or more
sparse page sizes that may be selected. The number of available page sizes
for an internal format and the dimensions of the pages may be determined
by calling GetInternalFormat* with the <pname> NUM_VIRTUAL_PAGE_SIZES_EXT
(for the number of available page sizes), VIRTUAL_PAGE_SIZE_X_EXT,
VIRTUAL_PAGE_SIZE_Y_EXT or VIRTUAL_PAGE_SIZE_Z_EXT (for the virtual
page widths, heights and depths, respectively). Not all internal formats
support sparse allocation. For those formats, the value of
NUM_VIRTUAL_PAGE_SIZES_EXT will be zero. The internal formats which are
guaranteed to support sparse allocation is listed in Table 8.13. Formats
not listed as supported in Table 8.13 may still be supported by some
implementations.

The VIRTUAL_PAGE_SIZE_INDEX_EXT may be used to select the page layout for
a sparse texture. The value of the texture's VIRTUAL_PAGE_SIZE_INDEX_EXT
parameter is treated as an index into the array of possible page sizes
for the type and requested internal format of the texture, and matches
index of the array of values returned for the VIRTUAL_PAGE_SIZE_{XYZ}_EXT
internal format query.

When a sparsely committed texture is accessed by the GL, accesses that
require only samples contained in committed regions complete as normal.
For operations that access samples from uncommitted regions produce
the following behavior:

* Reads from such regions produce undefined data, but otherwise have
no adverse effect. This includes samples required for the
implementation of texture filtering, mipmap generation and so on.

* Writes to such regions are ignored. The GL may attempt to write to
uncommitted regions but the effect of doing so will be benign.

* Atomic operations with return values on uncommitted regions will
complete normally, but the returned value will be undefined and the
result of the atomic operation will be discarded.

* Reads and writes through framebuffers shall have no adverse effect,
but fragment shaders corresponding to uncommitted regions of the
framebuffer still execute to completion. Visible side effects
of these shaders such as operations on atomic counters, storage
blocks or committed regions of images are still seen, as are
the results of operations such as occlusion queries.

* Access to uncommitted regions by the client (for example through
ReadPixels) shall have similar effect as through any
other part of the GL --- reads return undefined data and writes are
discarded, with no other ill effect.

Insert Subsection 8.17sparse.2. "Controlling Sparse Texture Commitment"

If a texture is allocated using sparse storage (that is, its
TEXTURE_SPARSE_EXT parameter is TRUE at the time that its storage is
allocated), it is initially created with only a virtual data store, and no
physical data store. Individual pages of a sparse texture may be made
resident or non-resident by calling

void TexPageCommitmentEXT(enum target,
int level,
int xoffset,
int yoffset,
int zoffset,
sizei width,
sizei height,
sizei depth,
boolean commit);

with <target> and <level> indicating the level of the texture object whose
residency is to be modified. <xoffset>, <yoffset>, <zoffset>, <width>,
<height> and <depth> are interpreted as they are in TexSubImage3D.  An
error will be generated unless <xoffset>, <yoffset> <zoffset>, <width>,
<height> and <depth> specify a region of the texture level that is aligned
to multiples of the page size or to the edges of the texture.

If the value of <commit> is TRUE, then the texture pages contained in
the region defined by the values of <xoffset>, <yoffset>, <zoffset>,
<width>, <height> and <depth> are committed. If they were not committed
before the call, then new physical backing store is allocated and associated
with the sparse pages and their initial content is undefined. If the pages
were already committed, then they remain committed, no error is generated,
and the content of those pages remains unmodified. If the value of
<committed> is FALSE, then the texture pages contained in the region are
made de-committed. Their physical store is de-allocated, and their contents
again become undefined.

For the purposes of commitment, a cube map texture is treated as a 2D
array texture with a depth of six and cube map array textures are treated
as 2D array textures with a depth equal to six times the number of layers
in the cube map array.

For levels of a sparse texture where each dimension is a multiple of the
virtual page size, the residency of individual page-size regions is
controlled by TexPageCommitmentEXT and such levels may be partially
populated.  When the mipmap chain reaches a level that is not an integer
multiple of the virtual page size in any dimension, padding and memory
layout considerations may make it impossible to treat that level and
subsequent smaller ones as partially populated.  The set of levels that
can be partially populated is implementation-dependent.  The total number
of levels that may be partially populated may be queried by calling
GetTexParameter* with the <pname> NUM_SPARSE_LEVELS_EXT.

The collection of texture levels that may not be partially populated, if
any, consists of levels NUM_SPARSE_LEVELS_EXT and higher, and is referred
to as the mipmap 'tail'.  The levels comprising the tail are made resident
or non-resident as a unit.  The tail is resident if and only if
TexPageCommitmentEXT has been called successfully with <level> greater
than or equal to NUM_SPARSE_LEVELS_EXT and the value of <commit> was TRUE
for the last such call.

Views of sparse textures are also considered sparse. Modifications to
commitment of a texture via a view of it affect the parent texture and
any other views containing the modified pages. If a view of a sparse
texture references its tail (or is entirely contained within it),
modifications to commitment of the tail via the view will affect the entire
tail of the parent, even for parts of the tail that are not referenced
by the view. Furthermore, modifications to tail commitment may affect
views referencing other parts of the tail.

Errors

An INVALID_OPERATION error is generated if <xoffset> + <width> or
<yoffset> + <height> is greater than the width or height, respectively,
of level <level> of the texture bound to <target>.

An INVALID_OPERATION error is generated if <zoffset> + <depth> is
greater than

* the depth of level <level> of the texture bound to <target>, if
<target> is TEXTURE_3D;

* the number of layers of level <level> of the texture bound to
<target>, if <target> is TEXTURE_2D_ARRAY;

* six times the number of layers of level <level> of the texture bound
to <target>, if <target> is TEXTURE_CUBE_MAP_ARRAY_OES; or

* one, for all other targets.

An INVALID_VALUE error is generated if <xoffset>, <yoffset>, or
<zoffset> is not a multiple of VIRTUAL_PAGE_SIZE_X_EXT,
VIRTUAL_PAGE_SIZE_Y_EXT, or VIRTUAL_PAGE_SIZE_Z_EXT, respectively, of
the texture bound to <target>.

An INVALID_OPERATION error is generated if <width> is not an integer
multiple of VIRTUAL_PAGE_SIZE_X_EXT and <width> plus <xoffset> is not
equal to the width of level <level> of the texture bound to <target>.

An INVALID_OPERATION error is generated if <height> is not an integer
multiple of VIRTUAL_PAGE_SIZE_Y_EXT and <height> plus <yoffset> is not
equal to the height of level <level> of the texture bound to <target>.

An INVALID_OPERATION error is generated if <depth> is not an integer
multiple of VIRTUAL_PAGE_SIZE_Z_EXT and <depth> plus <zoffset> is not
equal to

* the depth of level <level> of the texture bound to <target>, if
<target> is TEXTURE_3D;

* the number of layers of level <level> of the texture bound to
<target>, if <target> is TEXTURE_2D_ARRAY;

* six times the number of layers of level <level> of the texture bound
to <target>, if <target> is TEXTURE_CUBE_MAP_ARRAY; or

* one, for all other targets.

An INVALID_OPERATION error is generated if the value of
TEXTURE_IMMUTABLE_FORMAT or TEXTURE_SPARSE_EXT for the texture bound to
<target> is FALSE.

[[ The following is only added if EXT_direct_state_access is supported. ]]

The command

void TexturePageCommitmentEXT(uint texture,
int level,
int xoffset,
int yoffset,
int zoffset,
sizei width,
sizei height,
sizei depth,
boolean commit);

may also be used to control the residency of sparse textures.  This
command behaves identically to TexPageCommitmentEXT, except that the
texture is identified by the name <texture> instead of via <target>.

Errors

An INVALID_OPERATION error is generated if <texture> is not the name of
an existing texture.

All other errors listed for TexPageCommitmentEXT also apply to
TexturePageCommitmentEXT, except that references to "the texture bound
to <target>" should be replaced with "the texture <texture>", and all
other references to "<target>" should be replaced with "the target of
texture <texture>".

Additions to Chapter 19 of the OpenGL ES 3.1 Specification (Context State
Queries)

Append to Table 19.1, "Possible targets that internalformat can be used
with and the corresponding usage meaning"

+-------------------------------+-------------------------+
| Target                        | Usage                   |
+-------------------------------+-------------------------+
| TEXTURE_2D                    | 2D texture              |
| TEXTURE_2D_ARRAY              | 2D texture array        |
| TEXTURE_CUBE_MAP              | Cube map texture        |
| TEXTURE_CUBE_MAP_ARRAY_OES    | Cube map texture array  |
| TEXTURE_3D                    | 3D texture              |
+-------------------------------+-------------------------+

Modify Section 19.3.1, "Internal Format Query Parameters"

(In the first item on the supported pnames list for NUM_SAMPLE_COUNTS,
modify the first sub-list item "If <target> does not support multiple
samples..")

- If <internalformat> is not color-renderable, depth-renderable, or
stencil-renderable (as defined in section 9.4), or if <target> does
not support multiple samples (is not TEXTURE_2D_MULTISAMPLE. or
RENDERBUFFER), zero is returned.

(In the second item on the supported pnames list for SAMPLES, append to the
sub-list)

- If <internalformat> is not color-renderable, depth-renderable, or
stencil-renderable (as defined in section 9.4), or if <target> does
not support multiple samples (is not TEXTURE_2D_MULTISAMPLE. or
RENDERBUFFER), <params> is not modified.

(Add to supported pnames list)

* NUM_VIRTUAL_PAGE_SIZES_EXT: The number of virtual page sizes
supported by internalformat and target is written into params.
Unsupported internal formats and targets report 0.

* VIRTUAL_PAGE_SIZE_X_EXT: The virtual page widths supported for
internalformat and target are written into params.

* VIRTUAL_PAGE_SIZE_Y_EXT: The virtual page heights supported for
internalformat and target are written into params.

* VIRTUAL_PAGE_SIZE_Z_EXT: The virtual page depths supported for
internalformat and target are written into params.

In the error list on p.353, modify the first item:

* An INVALID_ENUM error is generated if <target> is not one of the targets
in table 19.1, or if <pname> is not SAMPLES, NUM_SAMPLES_COUNTS,
NUM_VIRTUAL_PAGE_SIZES_EXT, VIRTUAL_PAGE_SIZE_X_EXT,
VIRTUAL_PAGE_SIZE_Y_EXT or VIRTUAL_PAGE_SIZE_Z_EXT.

Remove the second item "An INVALID_ENUM error is generated if
internalformat is not color-, depth- or stencil-renderable."

Additions to the AGL/GLX/WGL/EGL Specifications

None.

GLX Protocol

None.

New State

Append to Table 20.9, "Textures (state per texture object) (cont.)"

+-----------------------------------+-------+---------------------+-----------------+---------------------------------------+-------------+
| Get Value                         | Type  | Get Command         | Initial Value   | Description                           | Sec.        |
+-----------------------------------+-------+---------------------+-----------------+---------------------------------------+-------------+
| VIRTUAL_PAGE_SIZE_INDEX_EXT       | Z+    | GetTexParameteriv   | 0               | Virtual page size index               | 8.17sparse  |
| TEXTURE_SPARSE_EXT                | B     | GetTexParameteriv   | FALSE           | Texture sparseness                    | 8.17sparse  |
| NUM_SPARSE_LEVELS_EXT             | Z+    | GetTexParameteriv   | 0               | Number of potentially sparse levels   | 8.17sparse  |
+-----------------------------------+-------+---------------------+-----------------+---------------------------------------+-------------+

New Implementation Dependent State

Append to Table 20.41, "Implementation Dependent Values"

+--------------------------------------------+-------+-------------+-----------------+---------------------------------------+-------+
| Get Value                                  | Type  | Get Command | Minimum Value   | Description                           | Sec.  |
+--------------------------------------------+-------+-------------+-----------------+---------------------------------------+-------+
| MAX_SPARSE_TEXTURE_SIZE_EXT                | Z+    | GetIntegerv | 2048            | Maximum 1D/2D/rectangle texture image | 8.19  |
|                                            |       |             |                 | dimension for a sparse texture.       |       |
| MAX_SPARSE_3D_TEXTURE_SIZE_EXT             | Z+    | GetIntegerv | 256             | Maximum 3D texture image dimension    | 8.19  |
|                                            |       |             |                 | for a sparse texture.                 |       |
| MAX_SPARSE_ARRAY_TEXTURE_LAYERS_EXT        | Z+    | GetIntegerv | 256             | Maximum number of layers in a sparse  | 8.19  |
|                                            |       |             |                 | array texture.                        |       |
| SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_EXT | B     | GetBooleanv | -               | TRUE if there are no restrictions on  | 8.19  |
|                                            |       |             |                 | the allocation of mipmaps in sparse   |       |
|                                            |       |             |                 | textures and FALSE otherwise.         |       |
+--------------------------------------------+-------+-------------+-----------------+---------------------------------------+-------+

(Note the values of MAX_SPARSE_TEXTURE_SIZE_EXT, MAX_SPARSE_3D_TEXTURE_SIZE_EXT,
MAX_SPARSE_ARRAY_TEXTURE_LAYERS_EXT must be at least as high as the
corresponding non-sparse maximums. These values were 16384, 2048, and
2048 respectively in ARB_sparse_texture, reflecting the desktop texture
size limits. They were reduced in this extension to reflect the ES 3.1
limits of 2048, 256, and 256.)

Dependencies on OES_texture_view and EXT_texture_view

If neither OES_texture_view nor EXT_texture_view is supported,
then remove all references to texture views.

Dependencies on OES_texture_border_clamp

If OES_texture_border_clamp is not supported, ignore all references
to TexParameterI{u}ivOES and GetTexParameterI{u}ivOES.

Dependencies on EXT_texture_border_clamp

If EXT_texture_border_clamp is not supported, ignore all references
to TexParameterI{u}ivEXT and GetTexParameterI{u}ivEXT.

Dependencies on OES_texture_cube_map_array and EXT_texture_cube_map_array

If neither OES_texture_cube_map_array nor EXT_texture_cube_map_array is
supported, ignore all references to cube map array textures and
TEXTURE_CUBE_MAP_ARRAY_OES.

If OES_texture_cube_map_array is not supported, but
EXT_texture_cube_map_array is, replace all occurrences of
TEXTURE_CUBE_MAP_ARRAY_OES with TEXTURE_CUBE_MAP_ARRAY_EXT.

Dependencies on EXT_texture_norm16

If EXT_texture_norm16 is not supported, remove references to
all texture formats added by that extension. These are:
R16_EXT, R16_SNORM_EXT, RG16_EXT, RG16_SNORM_EXT, RGB16_EXT,
RGB16_SNORM_EXT, RGBA16_EXT, and RGBA16_SNORM_EXT.

Dependencies on GL_EXT_direct_state_access

If the GL_EXT_direct_state_access extension is not supported, remove all
references to TexturePageCommitmentEXT.

Issues

Note: Issues 1-9 are the same as those in the OpenGL extension
ARB_sparse_texture, which can be found in the OpenGL Registry.
They were retained here to aid in understanding the functionality.

0) How does this extension differ from ARB_sparse_texture?

* It was rebased against OpenGL ES 3.1 and suffices converted from
ARB to EXT.  Interactions with ES extensions were added.
* References to functions and texture formats not present in
OpenGL ES were removed (GetDoublev, GetTexImage).

1) Do we want to mandate specific page sizes for specific formats?

RESOLVED. No, this functionality is available in EXT_sparse_texture2.

2) What happened to MIN_SPARSE_LEVEL_AMD from the AMD spec? Do we need it
here?

RESOLVED. We changed it to NUM_SPARSE_LEVELS_EXT. MIN_SPARSE_LEVEL_AMD
could not acceptably describe the case where a texture is technically
sparse, but no level of the texture may be sparsely populated. The
AMD specification disallowed creation of such a texture. However, this
extension does allow creation of a texture that is either wholly
resident or non-resident. Furthermore, if a view of a sparse texture
is created starting somewhere in the tail, then that whole view
is essentially sparse.

3) Should it be mandatory to support sparse allocation for compressed
textures?

RESOLVED: No, but in all likelihood, implementations will support some
or all compressed texture formats.

4) Are multisample textures supported? What about depth and stencil
format textures?

RESOLVED: No. Depth and stencil format textures are optional to support.
Providing support would be a case of reporting non-zero for
NUM_VIRTUAL_PAGE_SIZES_EXT for those formats. Multi-sample textures
are explicitly not supported by this extension as their targets are
excluded from TexStorage* support. Allowing support for these would
require a new extension, if only to remove the error generated
if one of the multi-sample targets is used with TexStorage* when
the sparse flag is set.

5) Do we need language clarifying completeness and the effects of
residency on completeness?

RESOLVED: Currently, there is no language. Textures allocated by
TexStorage* (which include all sparse textures) are always complete.
Residency doesn't effect that and sampling from them is well defined
(or explicitly undefined).

6) Can commitment fail? What happens if it does?

RESOLVED: An OUT_OF_MEMORY error is generated if physical backing cannot
be allocated for the previously allocated virtual space. No language
is added here as it is implicit that any command can generate
OUT_OF_MEMORY at any time for any reason... which includes new commands
introduced here.

7) Please explain, in plain English, what the rules are governing the size
of a texture's base level, mipmap levels, and the 'tail'.

The base level of the texture must be an integer multiple of the page
size in each dimension. This need not be a power of two or square or
anything of that nature. As we proceed along the mipmap chain, the
current level will become smaller and smaller, at each step halving in
size. At some point, the level dimensions will no longer be an integer
multiple of the page size, where the memory corresponding to that level
and smaller sized levels may not be evenly divided into pages.  The
memory allocated to such levels may not be naturally aligned on memory
page boundaries or may be too small to bother with partial residency.
Implementations are permitted to treat such a level and all subsequent
levels as either fully resident or fully non-resident.  We refer to
this set of levels as the mipmap "tail".  The set of levels belonging
to the tail is implementation-dependent.  Some implementations may
start the tail at the first level where any dimension is not the
multiple of a page size; others might pad out such allocations to page
boundaries and start the tail at a much smaller mipmap level.  The tail
is made resident or non-resident as a unit; the tail is resident if and
only if <resident> was TRUE for the last call to TexPageCommitmentEXT
when <level> was any value in the tail.

Clearly, making the base level a square power of two multiple of the
page size will mean that the greatest part of the texture can be sparse
and will minimize the size of the tail. However, it's perfectly legal,
with a hypothetical 256 x 256 texel page size to create a texture with
a base level of 4096 x 256. Such a texture can be sparse in the base
level, but level 1 would be 2048 x 128, which is no longer a multiple
of the page size, and therefore might be considered as the start of the
tail.

8) What's SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_EXT for?

Some implementations may store the mipmap chain for array textures
and cubemaps such that the presence and size of mipmaps affects the
alignment of the start of each layer, even in the base level. Consider
an implementation that stores all layers of level 0, then all of
level 1, then all of level 2 and so on. The presence of a mipmap chain
(or lack thereof) would have no effect on the alignment of layers 1
through N of the array (or cubemap faces). Now, consider an
implementation that stores all of the levels for layer 0, then all
levels of layer 1 and so on. The number and size of the levels of the
texture _would_ have an effect on the alignment of layers 1 through N
of the texture. If the size of the mipmap chain for a single layer
causes the next layer to become misaligned to the page size in linear
address space, then the texture cannot be sparsely populated. This flag
indicates whether the implementation has any restrictions on the size
of the mipmap chain. In particular, these restrictions ensure that,
while the texture may have mipmaps, the total size of the mipmap chain
for each level still satisfies the alignment restrictions required by
that implementation's virtual memory subsystem.

9) What happens when you create a view of a sparse texture?

RESOLVED: That view is sparse, as are views of that view and so on.
Also, if the view hits the tail, then modifications of tail residency
via the view affect the whole tail of the parent texture.

Revision History

Rev.    Date      Author    Changes
----  ----------  --------  -----------------------------------------
3    03/27/2015  dkoch     update status and contributors
2    02/25/2015  xiche     Additional interaction with GetInternalformativ
1    11/13/2014  dkoch     Initial version based on ARB_sparse_texture v11