EXT_sparse_texture2
Name
EXT_sparse_texture2
Name Strings
GL_EXT_sparse_texture2
Contact
Pat Brown, NVIDIA Corporation (pbrown 'at' nvidia.com)
Contributors
Jeff Bolz, NVIDIA Corporation
Mathias Heyer, NVIDIA Corporation
Daniel Koch, NVIDIA Corporation
Status
Shipping
Version
Last Modified Date: April 19, 2016
NVIDIA Revision: 3
Number
OpenGL Extension #463
OpenGL ES Extension #259
Dependencies
This extension is written against the OpenGL 4.4 Specification
(Compatibility Profile), dated July 21, 2013.
This extension is written against the OpenGL Shading Language
Specification, version 4.40, revision 6.
When implemented in OpenGL, this extension requires and extends
ARB_sparse_texture.
When implemented in OpenGL ES, this extension requires and extends
EXT_sparse_texture.
This extension interacts trivially with EXT_depth_bounds_test.
This extension interacts with NV_gpu_program4 and NV_gpu_program5.
This extension interacts with OpenGL ES 3.1 (dated October 29th 2014).
This extension interacts with OpenGL ES Shading Language 3.1 (revision 3).
This extension interacts with EXT_gpu_shader5 and OES_gpu_shader5.
This extension interacts with EXT_texture_norm16.
This extension interacts with EXT_texture_cube_map_array and
OES_texture_cube_map_array.
This extension interacts with OES_texture_storage_multisample_2D_array.
Overview
This extension builds on the ARB_sparse_texture extension, providing the
following new functionality:
* New built-in GLSL texture lookup and image load functions are provided
that return information on whether the texels accessed for the texture
lookup accessed uncommitted texture memory.
* New built-in GLSL texture lookup functions are provided that specify a
minimum level of detail to use for lookups where the level of detail
is computed automatically. This allows shaders to avoid accessing
unpopulated portions of high-resolution levels of detail when it knows
that the memory accessed is unpopulated, either from a priori
knowledge or from feedback provided by the return value of previously
executed "sparse" texture lookup functions.
* Reads of uncommitted texture memory will act as though such memory
were filled with zeroes; previously, the values returned by reads were
undefined.
* Standard implementation-independent virtual page sizes for internal
formats required to be supported with sparse textures. These standard
sizes can be requested by leaving VIRTUAL_PAGE_SIZE_INDEX_ARB at its
initial value (0).
* Support for creating sparse multisample and multisample array textures
is added. However, the virtual page sizes for such textures remain
fully implementation-dependent.
New Procedures and Functions
None.
New Tokens
None.
Modifications to the OpenGL 4.4 Specification (Compatibility Profile)
Modify Section 8.10, Texture Parameters, p. 250
(modify the following Errors section entry for TexParameter*, added by
ARB_sparse_texture, to allow for sparse multisample and multisample array
textures)
INVALID_VALUE is generated if <pname> is TEXTURE_SPARSE_ARB, <pname>
is TRUE and <target> is not one of TEXTURE_2D, TEXTURE_2D_ARRAY,
TEXTURE_CUBE_MAP, TEXTURE_CUBE_MAP_ARRAY, TEXTURE_3D, TEXTURE_RECTANGLE,
TEXTURE_2D_MULTISAMPLE, or TEXTURE_2D_MULTISAMPLE_ARRAY.
Modify Section 8.14.1, Scale Factor and Level of Detail, p. 261
(move the next-to-last paragraph, p. 261, describing lod_min and lod_max
in equation 8.6, up one paragraph and modify it to read as follows)
lod_min and lod_max indicate minimum and maximum clamps on the computed
level of detail. lod_max is taken directly from the TEXTURE_MAX_LOD
texture or sampler parameter. If a texture access is performed in a
fragment shader with a minimum level of detail clamp specified in the
built-in texture lookup function, lod_min is the larger of the
TEXTURE_MIN_LOD texture or sampler parameter and the minimum level of
detail provided by the shader. Otherwise, lod_min is taken directly from
the TEXTURE_MIN_LOD texture or sampler parameter. The initial values of
the TEXTURE_MIN_LOD and TEXTURE_MAX_LOD texture and sampler parameters are
chosen so as to never clamp the range of lambda values.
Modify the edits to Section 8.19 (Immutable-Format Texture Images), as
made by ARB_sparse_texture
(remove the following language from the "p. 233" edits starting with "If
TEXTURE_SPARSE_ARB is TRUE"; there is no longer a restriction on the base
size of a sparse texture allocation)
[REMOVED LANGUAGE] ... 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. ...
(remove the following TexStorage error added by ARB_sparse_texture; there
is no longer a restriction on the base size of a sparse texture
allocation)
[REMOVED LANGUAGE] An INVALID_VALUE error is generated if
TEXTURE_SPARSE_ARB is TRUE and <width>, <height> or <depth> is is not an
integer multiple of the page size in the corresponding dimension.
(remove the error language beginning with "If the value of
SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_ARB is FALSE", and replace with
the following)
In older extensions supporting sparse textures, the constant
SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_ARB was provided to advertise
implementation-dependent limitations potentially prohibiting the
allocation of array or cube map textures with full mipmap chains. No such
limitations apply in this extension. This constant is retained for
backwards compatibility, but all implementations of this extension must
return TRUE.
Modify Section 8.20.1 of ARB_sparse_texture (Allocation of and Access to
Sparse Textures)
(insert after the two paragraphs discussing VIRTUAL_PAGE_SIZE_INDEX_ARB)
When leaving the VIRTUAL_PAGE_SIZE_INDEX_ARB texture parameter at its
initial value (0), the virtual page size for many non-multisample sparse
textures can be found in Table 8.X. The virtual page size of such a
texture comes from the value listed in the "3D Page Size" column for the
texture target TEXTURE_3D, or the value listed in the "2D Page Size"
column for any other target. If the internal format of the texture is not
listed in Table 8.X or if the texture target is TEXTURE_2D_MULTISAMPLE or
TEXTURE_2D_MULTISAMPLE_ARRAY, the virtual page size for index zero is
fully implementation-dependent.
Internal Format 2D Page Size 3D Page Size
--------------- ------------- ------------
R8 256 x 256 x 1 64 x 32 x 32
R8_SNORM
R8I
R8UI
R16 256 x 128 x 1 32 x 32 x 32
R16_SNORM
RG8
RG8_SNORM
RGB565
R16F
R16I
R16UI
RG8I
RG8UI
RG16 128 x 128 x 1 32 x 32 x 16
RG16_SNORM
RGBA8
RGBA8_SNORM
RGB10_A2
RGB10_A2UI
RG16F
R32F
R11F_G11F_B10F
RGB9_E5
R32I
R32UI
RG16I
RG16UI
RGBA8I
RGBA8UI
RGBA16 128 x 64 x 1 32 x 16 x 16
RGBA16_SNORM
RGBA16F
RG32F
RG32I
RG32UI
RGBA16I
RGBA16UI
RGBA32F 64 x 64 x 1 16 x 16 x 16
RGBA32I
RGBA32UI
Table 8.X, Standard Virtual Page Sizes for Sparse Textures
(modify first bullet under "When a sparsely committed texture is accessed
by the GL" at the end of the section)
* Reads from such regions behave as if the data in texture memory for
all components present in the texture format were zero. This
includes samples required for the implementation of texture
filtering, image loads, mipmap generation, and so on. For texture
and image loads, components not present in the texture format (e.g.,
alpha in a texture with an RGB base internal format) will return
default values, as in non-sparse textures.
(modify third bullet under "When a sparsely committed texture is accessed
by the GL" at the end of the section)
* Atomic operations operating on uncommitted regions will not generate
exceptions but will always return zero. The result of the atomic
operation, which is normally written to memory, will instead be
discarded.
(add new bullets under "When a sparsely committed texture is accessed by
the GL" at the end of the section)
* When performing the stencil test (section 17.3.5), depth buffer test
(section 17.3.6), or depth bounds test on pixels in uncommitted
regions, the results of the test will be consistent with reading a
value of zero from the framebuffer. No value is written to the
depth buffer.
(add a new paragraph at the end of the section)
The OpenGL Shading Language provides built-in functions that perform a
texture fetch or image load and return sparse texture status information
to the caller. The status information can be queried by the built-in
function sparseTexelsResidentEXT(), which returns false if the lookup
function read one or more uncommitted texels and true otherwise. For the
purposes of this query, texels addressed by a filter normally computing a
weighted average of multiple texels (e.g., LINEAR) will be considered to
access only those texels with non-zero weights.
Modify Section 8.20.2 of ARB_sparse_texture (Controlling Sparse Texture
Commitment)
(modify the fifth paragraph of the section from ARB_sparse_texture,
starting with "For levels of a sparse texture where..." to guarantee that
any level greater than or equal to the page size in all dimensions can be
sparsely populated)
For levels of a sparse texture where each dimension is greater than or
equal to of the virtual page size, the residency of individual page-size
regions is controlled by TexPageCommitmentARB and such levels may be
partially populated. When the mipmap chain reaches a level that is not
greater than or equal to 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. ...
Modifications to the OpenGL Shading Language Specification, Version 4.40
Including the following line in a shader can be used to control the
language features described in this extension:
#extension GL_EXT_sparse_texture2 : <behavior>
where <behavior> is as specified in section 3.3.
New preprocessor #defines are added to the OpenGL Shading Language:
#define GL_EXT_sparse_texture2 1
Modify Section 8.9, Texture Functions, p. 151
(insert after first paragraph, p. 152)
The texture lookup functions with an <lodClamp> parameter specify a
minimum clamp applied to the automatic level of detail computations.
Since automatic level of detail calculations are only supported by
fragment shaders, these lookup functions are also only available in
fragment shaders. No functions with the <lodClamp> parameter are provided
for rectangle textures, multisample textures, and texture buffers because
mipmaps are not allowed for these types of textures.
Modify Section 8.9.2, Texel Lookup Functions, p. 155
(This extension adds two new variants of texture lookup functions. The
"sparse" functions are like normal texture lookup functions, except that
they return a sparse texture residency status to the caller and return the
actual filtered texel value in an "out" parameter. The "Clamp" variants
are functions adding a new parameter specifying a minimum LOD to use for
texture lookup functions where level of detail is computed automatically.
For each set of texture functions, we provide one to three new variants
based on whether sparse and LOD clamping functionality are desired. These
new variants copy the existing functions, add suffixes to the function
names, and add one or more new parameters.
We create new variants only for the targets for which sparse storage is
supported -- no new functions are added for the following sampler types:
gsampler1D, sampler1DShadow, gsampler1DArray, sampler1DArrayShadow.
Additionally, to reduce the number of new functions added, we are not
including any new variants for textureProj*() built-ins. To use the new
features with projective texture lookups, shaders can divide through by q
and use non-projective variants. We also chose not to provide "Clamp"
variants of functions like textureLod() expecting an explicit
level-of-detail.)
(insert new lookup function table cells, at the end of the section,
p. 161)
Syntax:
int sparseTextureEXT(gsampler2D sampler, vec2 P,
out gvec4 texel [, float bias]);
int sparseTextureEXT(gsampler3D sampler, vec3 P,
out gvec4 texel [, float bias]);
int sparseTextureEXT(gsamplerCube sampler, vec3 P,
out gvec4 texel [, float bias]);
int sparseTextureEXT(sampler2DShadow sampler, vec3 P,
out float texel [, float bias]);
int sparseTextureEXT(samplerCubeShadow sampler, vec4 P,
out float texel [, float bias]);
int sparseTextureEXT(gsampler2DArray sampler, vec3 P,
out gvec4 texel [, float bias]);
int sparseTextureEXT(gsamplerCubeArray sampler, vec4 P,
out gvec4 texel [, float bias]);
int sparseTextureEXT(sampler2DArrayShadow sampler, vec4 P,
out float texel);
int sparseTextureEXT(gsampler2DRect sampler, vec2 P,
out gvec4 texel);
int sparseTextureEXT(sampler2DRectShadow sampler, vec3 P,
out float texel);
int sparseTextureEXT(samplerCubeArrayShadow sampler, vec4 P,
float compare, out float texel);
Description:
Do a filtered texture lookup as in texture(), but return texture access
residency information from the function and the filtered lookup result in
the out parameter <texel>.
--
Syntax:
int sparseTextureClampEXT(gsampler2D sampler, vec2 P,
float lodClamp, out gvec4 texel
[, float bias]);
int sparseTextureClampEXT(gsampler3D sampler, vec3 P,
float lodClamp, out gvec4 texel
[, float bias]);
int sparseTextureClampEXT(gsamplerCube sampler, vec3 P,
float lodClamp, out gvec4 texel
[, float bias]);
int sparseTextureClampEXT(sampler2DShadow sampler, vec3 P,
float lodClamp, out float texel
[, float bias]);
int sparseTextureClampEXT(samplerCubeShadow sampler, vec4 P,
float lodClamp, out float texel
[, float bias]);
int sparseTextureClampEXT(gsampler2DArray sampler, vec3 P,
float lodClamp, out gvec4 texel
[, float bias]);
int sparseTextureClampEXT(gsamplerCubeArray sampler, vec4 P,
float lodClamp, out gvec4 texel
[, float bias]);
int sparseTextureClampEXT(sampler2DArrayShadow sampler, vec4 P,
float lodClamp, out float texel);
int sparseTextureClampEXT(samplerCubeArrayShadow sampler, vec4 P,
float compare, float lodClamp,
out float texel);
Description:
Do a filtered texture lookup as in texture(), but return texture access
residency information from the function and the filtered lookup result in
the out parameter <texel>. Additionally, clamp the automatically computed
level of detail to be greater than or equal to <lodClamp>.
--
Syntax:
gvec4 textureClampEXT(gsampler1D sampler, float P,
float lodClamp [, float bias]);
gvec4 textureClampEXT(gsampler2D sampler, vec2 P,
float lodClamp [, float bias]);
gvec4 textureClampEXT(gsampler3D sampler, vec3 P,
float lodClamp [, float bias]);
gvec4 textureClampEXT(gsamplerCube sampler, vec3 P,
float lodClamp [, float bias]);
float textureClampEXT(sampler1DShadow sampler, vec3 P,
float lodClamp [, float bias]);
float textureClampEXT(sampler2DShadow sampler, vec3 P,
float lodClamp [, float bias]);
float textureClampEXT(samplerCubeShadow sampler, vec4 P,
float lodClamp [, float bias]);
gvec4 textureClampEXT(gsampler1DArray sampler, vec2 P,
float lodClamp [, float bias]);
gvec4 textureClampEXT(gsampler2DArray sampler, vec3 P,
float lodClamp [, float bias]);
gvec4 textureClampEXT(gsamplerCubeArray sampler, vec4 P,
float lodClamp [, float bias]);
float textureClampEXT(sampler1DArrayShadow sampler, vec3 P,
float lodClamp [, float bias]);
float textureClampEXT(sampler2DArrayShadow sampler, vec4 P,
float lodClamp);
float textureClampEXT(samplerCubeArrayShadow sampler, vec4 P,
float compare, float lodClamp);
Description:
Do a filtered texture lookup as in texture(), but clamp the automatically
computed level of detail to be greater than or equal to <lodClamp>.
--
Syntax:
int sparseTextureLodEXT(gsampler2D sampler, vec2 P, float lod,
out gvec4 texel);
int sparseTextureLodEXT(gsampler3D sampler, vec3 P, float lod,
out gvec4 texel);
int sparseTextureLodEXT(gsamplerCube sampler, vec3 P, float lod,
out gvec4 texel);
int sparseTextureLodEXT(sampler2DShadow sampler, vec3 P, float lod,
out float texel);
int sparseTextureLodEXT(gsampler2DArray sampler, vec3 P, float lod,
out gvec4 texel);
int sparseTextureLodEXT(gsamplerCubeArray sampler, vec4 P, float lod,
out gvec4 texel);
Description:
Do a filtered texture lookup as in textureLod(), but return texture access
residency information from the function and the filtered lookup result in
the out parameter <texel>.
--
Syntax:
int sparseTextureOffsetEXT(gsampler2D sampler, vec2 P,
ivec2 offset, out gvec4 texel
[, float bias]);
int sparseTextureOffsetEXT(gsampler3D sampler, vec3 P,
ivec3 offset, out gvec4 texel
[, float bias]);
int sparseTextureOffsetEXT(gsampler2DRect sampler, vec2 P,
ivec2 offset, out gvec4 texel);
int sparseTextureOffsetEXT(sampler2DRectShadow sampler, vec3 P,
ivec2 offset, out float texel);
int sparseTextureOffsetEXT(sampler2DShadow sampler, vec3 P,
ivec2 offset, out float texel
[, float bias]);
int sparseTextureOffsetEXT(gsampler2DArray sampler, vec3 P,
ivec2 offset, out gvec4 texel
[, float bias]);
int sparseTextureOffsetEXT(sampler2DArrayShadow sampler, vec4 P,
ivec2 offset, out float texel);
Description:
Do a filtered texture lookup as in textureOffset(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>.
--
Syntax:
int sparseTextureOffsetClampEXT(gsampler2D sampler, vec2 P,
ivec2 offset, float lodClamp,
out gvec4 texel [, float bias]);
int sparseTextureOffsetClampEXT(gsampler3D sampler, vec3 P,
ivec3 offset, float lodClamp,
out gvec4 texel [, float bias]);
int sparseTextureOffsetClampEXT(sampler2DShadow sampler, vec3 P,
ivec2 offset, float lodClamp,
out float texel [, float bias]);
int sparseTextureOffsetClampEXT(gsampler2DArray sampler, vec3 P,
ivec2 offset, float lodClamp,
out gvec4 texel [, float bias]);
int sparseTextureOffsetClampEXT(sampler2DArrayShadow sampler, vec4 P,
ivec2 offset, float lodClamp,
out float texel);
Description:
Do a filtered texture lookup as in textureOffset(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>. Additionally, clamp the
automatically computed level of detail to be greater than or equal to
<lodClamp>.
--
Syntax:
gvec4 textureOffsetClampEXT(gsampler1D sampler, float P,
int offset, float lodClamp [, float bias]);
gvec4 textureOffsetClampEXT(gsampler2D sampler, vec2 P,
ivec2 offset, float lodClamp [, float bias]);
gvec4 textureOffsetClampEXT(gsampler3D sampler, vec3 P,
ivec3 offset, float lodClamp [, float bias]);
float textureOffsetClampEXT(sampler1DShadow sampler, vec3 P,
int offset, float lodClamp [, float bias]);
float textureOffsetClampEXT(sampler2DShadow sampler, vec3 P,
ivec2 offset, float lodClamp [, float bias]);
gvec4 textureOffsetClampEXT(gsampler1DArray sampler, vec2 P,
int offset, float lodClamp [, float bias]);
gvec4 textureOffsetClampEXT(gsampler2DArray sampler, vec3 P,
ivec2 offset, float lodClamp [, float bias]);
float textureOffsetClampEXT(sampler1DArrayShadow sampler, vec3 P,
int offset, float lodClamp [, float bias]);
float textureOffsetClampEXT(sampler2DArrayShadow sampler, vec4 P,
ivec2 offset, float lodClamp);
Description:
Do a filtered texture lookup as in textureOffset(), but clamp the
automatically computed level of detail to be greater than or equal to
<lodClamp>.
--
Syntax:
int sparseTexelFetchEXT(gsampler2D sampler, ivec2 P, int lod,
out gvec4 texel);
int sparseTexelFetchEXT(gsampler3D sampler, ivec3 P, int lod,
out gvec4 texel);
int sparseTexelFetchEXT(gsampler2DRect sampler, ivec2 P,
out gvec4 texel);
int sparseTexelFetchEXT(gsampler2DArray sampler, ivec3 P, int lod,
out gvec4 texel);
int sparseTexelFetchEXT(gsampler2DMS sampler, ivec2 P, int sample,
out gvec4 texel);
int sparseTexelFetchEXT(gsampler2DMSArray sampler, ivec3 P, int sample,
out gvec4 texel);
Description:
Do a single texel fetch as in texelFetch(), but return texture access
residency information from the function and the fetched texel in the out
parameter <texel>.
--
Syntax:
int sparseTexelFetchOffsetEXT(gsampler2D sampler, ivec2 P, int lod,
ivec2 offset, out gvec4 texel);
int sparseTexelFetchOffsetEXT(gsampler3D sampler, ivec3 P, int lod,
ivec3 offset, out gvec4 texel);
int sparseTexelFetchOffsetEXT(gsampler2DRect sampler, ivec2 P,
ivec2 offset, out gvec4 texel);
int sparseTexelFetchOffsetEXT(gsampler2DArray sampler, ivec3 P, int lod,
ivec2 offset, out gvec4 texel);
Description:
Do a single texel fetch as in texelFetchOffset(), but return texture
access residency information from the function and the fetched texel in
the out parameter <texel>.
--
Syntax:
int sparseTextureLodOffsetEXT(gsampler2D sampler, vec2 P,
float lod, ivec2 offset,
out gvec4 texel);
int sparseTextureLodOffsetEXT(gsampler3D sampler, vec3 P,
float lod, ivec3 offset,
out gvec4 texel);
int sparseTextureLodOffsetEXT(sampler2DShadow sampler, vec3 P,
float lod, ivec2 offset,
out float texel);
int sparseTextureLodOffsetEXT(gsampler2DArray sampler, vec3 P,
float lod, ivec2 offset,
out gvec4 texel);
Description:
Do a filtered texture lookup as in textureLodOffset(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>.
--
Syntax:
int sparseTextureGradEXT(gsampler2D sampler, vec2 P,
vec2 dPdx, vec2 dPdy,
out gvec4 texel);
int sparseTextureGradEXT(gsampler3D sampler, vec3 P,
vec3 dPdx, vec3 dPdy,
out gvec4 texel);
int sparseTextureGradEXT(gsamplerCube sampler, vec3 P,
vec3 dPdx, vec3 dPdy,
out gvec4 texel);
int sparseTextureGradEXT(gsampler2DRect sampler, vec2 P,
vec2 dPdx, vec2 dPdy,
out gvec4 texel);
int sparseTextureGradEXT(sampler2DRectShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy,
out float texel);
int sparseTextureGradEXT(sampler2DShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy,
out float texel);
int sparseTextureGradEXT(samplerCubeShadow sampler, vec4 P,
vec3 dPdx, vec3 dPdy,
out float texel);
int sparseTextureGradEXT(gsampler2DArray sampler, vec3 P,
vec2 dPdx, vec2 dPdy,
out gvec4 texel);
int sparseTextureGradEXT(sampler2DArrayShadow sampler, vec4 P,
vec2 dPdx, vec2 dPdy,
out float texel);
int sparseTextureGradEXT(gsamplerCubeArray sampler, vec4 P,
vec3 dPdx, vec3 dPdy,
out gvec4 texel);
Description:
Do a filtered texture lookup as in textureGrad(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>.
--
Syntax:
int sparseTextureGradClampEXT(gsampler2D sampler, vec2 P,
vec2 dPdx, vec2 dPdy, float lodClamp,
out gvec4 texel);
int sparseTextureGradClampEXT(gsampler3D sampler, vec3 P,
vec3 dPdx, vec3 dPdy, float lodClamp,
out gvec4 texel);
int sparseTextureGradClampEXT(gsamplerCube sampler, vec3 P,
vec3 dPdx, vec3 dPdy, float lodClamp,
out gvec4 texel);
int sparseTextureGradClampEXT(sampler2DShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy, float lodClamp,
out float texel);
int sparseTextureGradClampEXT(samplerCubeShadow sampler, vec4 P,
vec3 dPdx, vec3 dPdy, float lodClamp,
out float texel);
int sparseTextureGradClampEXT(gsampler2DArray sampler, vec3 P,
vec2 dPdx, vec2 dPdy, float lodClamp,
out gvec4 texel);
int sparseTextureGradClampEXT(sampler2DArrayShadow sampler, vec4 P,
vec2 dPdx, vec2 dPdy, float lodClamp,
out float texel);
int sparseTextureGradClampEXT(gsamplerCubeArray sampler, vec4 P,
vec3 dPdx, vec3 dPdy, float lodClamp,
out gvec4 texel);
Description:
Do a filtered texture lookup as in textureGrad(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>. Additionally, clamp the
automatically computed level of detail to be greater than or equal to
<lodClamp>.
--
Syntax:
gvec4 textureGradClampEXT(gsampler1D sampler, float P,
float dPdx, float dPdy, float lodClamp);
gvec4 textureGradClampEXT(gsampler2D sampler, vec2 P,
vec2 dPdx, vec2 dPdy, float lodClamp);
gvec4 textureGradClampEXT(gsampler3D sampler, vec3 P,
vec3 dPdx, vec3 dPdy, float lodClamp);
gvec4 textureGradClampEXT(gsamplerCube sampler, vec3 P,
vec3 dPdx, vec3 dPdy, float lodClamp);
float textureGradClampEXT(sampler1DShadow sampler, vec3 P,
float dPdx, float dPdy, float lodClamp);
float textureGradClampEXT(sampler2DShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy, float lodClamp);
float textureGradClampEXT(samplerCubeShadow sampler, vec4 P,
vec3 dPdx, vec3 dPdy, float lodClamp);
gvec4 textureGradClampEXT(gsampler1DArray sampler, vec2 P,
float dPdx, float dPdy, float lodClamp);
gvec4 textureGradClampEXT(gsampler2DArray sampler, vec3 P,
vec2 dPdx, vec2 dPdy, float lodClamp);
float textureGradClampEXT(sampler1DArrayShadow sampler, vec3 P,
float dPdx, float dPdy, float lodClamp);
float textureGradClampEXT(sampler2DArrayShadow sampler, vec4 P,
vec2 dPdx, vec2 dPdy, float lodClamp);
gvec4 textureGradClampEXT(gsamplerCubeArray sampler, vec4 P,
vec3 dPdx, vec3 dPdy, float lodClamp);
Description:
Do a filtered texture lookup as in textureGrad(), but clamp the
automatically computed level of detail to be greater than or equal to
<lodClamp>.
--
Syntax:
int sparseTextureGradOffsetEXT(gsampler2D sampler, vec2 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
out gvec4 texel);
int sparseTextureGradOffsetEXT(gsampler3D sampler, vec3 P,
vec3 dPdx, vec3 dPdy, ivec3 offset,
out gvec4 texel);
int sparseTextureGradOffsetEXT(gsampler2DRect sampler, vec2 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
out gvec4 texel);
int sparseTextureGradOffsetEXT(sampler2DRectShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
out float texel);
int sparseTextureGradOffsetEXT(sampler2DShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
out float texel);
int sparseTextureGradOffsetEXT(gsampler2DArray sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
out gvec4 texel);
int sparseTextureGradOffsetEXT(sampler2DArrayShadow sampler, vec4 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
out float texel);
Description:
Do a filtered texture lookup as in textureGradOffset(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>.
--
Syntax:
int sparseTextureGradOffsetClampEXT(gsampler2D sampler, vec2 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp, out gvec4 texel);
int sparseTextureGradOffsetClampEXT(gsampler3D sampler, vec3 P,
vec3 dPdx, vec3 dPdy, ivec3 offset,
float lodClamp, out gvec4 texel);
int sparseTextureGradOffsetClampEXT(sampler2DShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp, out float texel);
int sparseTextureGradOffsetClampEXT(gsampler2DArray sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp, out gvec4 texel);
int sparseTextureGradOffsetClampEXT(sampler2DArrayShadow sampler, vec4 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp, out float texel);
Description:
Do a filtered texture lookup as in textureGradOffset(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>. Additionally, clamp the
automatically computed level of detail to be greater than or equal to
<lodClamp>.
--
Syntax:
gvec4 textureGradOffsetClampEXT(gsampler1D sampler, float P,
float dPdx, float dPdy, int offset,
float lodClamp);
gvec4 textureGradOffsetClampEXT(gsampler2D sampler, vec2 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp);
gvec4 textureGradOffsetClampEXT(gsampler3D sampler, vec3 P,
vec3 dPdx, vec3 dPdy, ivec3 offset,
float lodClamp);
float textureGradOffsetClampEXT(sampler1DShadow sampler, vec3 P,
float dPdx, float dPdy, int offset,
float lodClamp);
float textureGradOffsetClampEXT(sampler2DShadow sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp);
gvec4 textureGradOffsetClampEXT(gsampler1DArray sampler, vec2 P,
float dPdx, float dPdy, int offset,
float lodClamp);
gvec4 textureGradOffsetClampEXT(gsampler2DArray sampler, vec3 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp);
float textureGradOffsetClampEXT(sampler1DArrayShadow sampler, vec3 P,
float dPdx, float dPdy, int offset,
float lodClamp);
float textureGradOffsetClampEXT(sampler2DArrayShadow sampler, vec4 P,
vec2 dPdx, vec2 dPdy, ivec2 offset,
float lodClamp);
Description:
Do a filtered texture lookup as in textureGrad(), but clamp the
automatically computed level of detail to be greater than or equal to
<lodClamp>.
Modify Section 8.9.3, Texel Gather Functions, p. 161
(insert new lookup function table cells, at the end of the section,
p. 163)
Syntax:
int sparseTextureGatherEXT(gsampler2D sampler, vec2 P,
out gvec4 texel [, int comp]);
int sparseTextureGatherEXT(gsampler2DArray sampler, vec3 P,
out gvec4 texel [, int comp]);
int sparseTextureGatherEXT(gsamplerCube sampler, vec3 P,
out gvec4 texel [, int comp]);
int sparseTextureGatherEXT(gsamplerCubeArray sampler, vec4 P,
out gvec4 texel [, int comp]);
int sparseTextureGatherEXT(gsampler2DRect sampler, vec2 P,
out gvec4 texel [, int comp]);
int sparseTextureGatherEXT(gsampler2DShadow sampler, vec2 P,
float refZ, out vec4 texel);
int sparseTextureGatherEXT(gsampler2DArrayShadow sampler, vec3 P,
float refZ, out vec4 texel);
int sparseTextureGatherEXT(gsamplerCubeShadow sampler, vec3 P,
float refZ, out vec4 texel);
int sparseTextureGatherEXT(gsamplerCubeArrayShadow sampler, vec4 P,
float refZ, out vec4 texel);
int sparseTextureGatherEXT(gsampler2DRectShadow sampler, vec2 P,
float refZ, out vec4 texel);
Description:
Do a texture gather operation as in textureGather(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>.
--
Syntax:
int sparseTextureGatherOffsetEXT(gsampler2D sampler, vec2 P,
ivec2 offset, out gvec4 texel
[, int comp]);
int sparseTextureGatherOffsetEXT(gsampler2DArray sampler, vec3 P,
ivec2 offset, out gvec4 texel
[, int comp]);
int sparseTextureGatherOffsetEXT(gsampler2DRect sampler, vec2 P,
ivec2 offset, out gvec4 texel
[, int comp]);
int sparseTextureGatherOffsetEXT(gsampler2DShadow sampler, vec2 P,
float refZ, ivec2 offset,
out vec4 texel);
int sparseTextureGatherOffsetEXT(gsampler2DArrayShadow sampler, vec3 P,
float refZ, ivec2 offset,
out vec4 texel);
int sparseTextureGatherOffsetEXT(gsampler2DRectShadow sampler, vec2 P,
float refZ, ivec2 offset,
out vec4 texel);
Description:
Do a texture gather operation as in textureGatherOffset(), but return
texture access residency information from the function and the filtered
lookup result in the out parameter <texel>.
--
Syntax:
int sparseTextureGatherOffsetsEXT(gsampler2D sampler, vec2 P,
ivec2 offsets[4], out gvec4 texel
[, int comp]);
int sparseTextureGatherOffsetsEXT(gsampler2DArray sampler, vec3 P,
ivec2 offsets[4], out gvec4 texel
[, int comp]);
int sparseTextureGatherOffsetsEXT(gsampler2DRect sampler, vec2 P,
ivec2 offsets[4], out gvec4 texel
[, int comp]);
int sparseTextureGatherOffsetsEXT(gsampler2DShadow sampler, vec2 P,
float refZ, ivec2 offsets[4],
out vec4 texel);
int sparseTextureGatherOffsetsEXT(gsampler2DArrayShadow sampler, vec3 P,
float refZ, ivec2 offsets[4],
out vec4 texel);
int sparseTextureGatherOffsetsEXT(gsampler2DRectShadow sampler, vec2 P,
float refZ, ivec2 offsets[4],
out vec4 texel);
Description:
Do a texture gather operation as in textureGatherOffset(), but return
texture access residency information from the function and the filtered
lookup result in the out parameter <texel>.
Add to the end of Section 8.12, Image Functions, p. 167
(insert new lookup function table cells, at the end of the section,
p. 170)
Syntax:
int sparseImageLoadEXT(gimage2D image, ivec2 P,
out gvec4 texel);
int sparseImageLoadEXT(gimage3D image, ivec3 P,
out gvec4 texel);
int sparseImageLoadEXT(gimage2DRect image, ivec2 P,
out gvec4 texel);
int sparseImageLoadEXT(gimageCube image, ivec3 P,
out gvec4 texel);
int sparseImageLoadEXT(gimage2DArray image, ivec3 P,
out gvec4 texel);
int sparseImageLoadEXT(gimageCubeArray image, ivec3 P,
out gvec4 texel);
int sparseImageLoadEXT(gimage2DMS image, ivec2 P, int sample,
out gvec4 texel);
int sparseImageLoadEXT(gimage2DMSArray image, ivec3 P, int sample,
out gvec4 texel);
Description:
Loads a texel from the image <image> as in imageLoad(), but return texture
access residency information from the function and the filtered lookup
result in the out parameter <texel>.
Add to the end of Section 8.17, Shader Memory Control Functions, p. 178
Many of the built-in texture lookup functions in sections 8.9.2 and 8.9.3
and the sparseImageLoad() function in section 8.12 can be used to return
sparse texture residency information in addition to texel values. In
these functions, the sparse texture residency information is returned by
the function as an integer and the texel values are returned in the output
parameter <texel>. The residency information can be interpreted by a
built-in function to determine if the lookup accessed any uncommitted
texels.
Syntax:
bool sparseTexelsResidentEXT(int code);
Description:
Returns false if any of the texels accessed by the sparse texture lookup
generating <code> were in uncommitted texture memory, and true
otherwise.
Additions to the AGL/GLX/WGL Specifications
None.
Errors
None.
New State
None.
New Implementation Dependent State
None.
Dependencies on OpenGL ES 3.1
Replace references to ARB_sparse_texture with references to
EXT_sparse_texture, in particular functions and enums introduced by
EXT_sparse_texture will carry EXT suffixes.
If implemented on OpenGL ES 3.1, remove all references to 1D and
rectangle textures and their respective texture targets (TEXTURE_1D
and TEXTURE_RECTANGLE). Also ignore the corresponding sampler
built-ins thereof: 'gsampler1D', 'gsampler2DRect' and
'gsampler2DRectShadow'. Do not introduce overloads of
sparseTexture*EXT, texture*ClampEXT or sparseTexelFetchEXT for these
sampler types.
Do not introduce sparseImageLoadEXT overloads of gimageRect,
gimage2D, gimage2DArray, gimage2DMS and gimage2DArrayMS.
Dependencies on EXT_texture_norm16
If implemented on OpenGL ES 3.1 and EXT_texture_norm16 is not
supported ignore all references to R16, RG16, RGBA16, R16_SNORM,
RG16_SNORM and RGBA16_SNORM. If EXT_texture_norm16 is supported,
these enums are suffixed by _EXT.
Dependencies on EXT_texture_cube_map_array and OES_texture_cube_map_array
If implemented on OpenGL ES 3.1 and neither EXT_texture_cube_map_array
nor OES_texture_cube_map_array is supported, ignore all references to
texture sampler types 'gsamplerCubeArray' and 'gsamplerCubeArrayShadow'.
Do not introduce overloads of sparseTexture*EXT, texture*ClampEXT or
sparseTexelFetchEXT for these sampler types. Remove references to
TEXTURE_CUBE_MAP_ARRAY.
Dependencies on OES_texture_storage_multisample_2D_array
If implemented on OpenGL ES 3.1 and OES_texture_storage_-
multisample_2D_array is not supported, ignore all references to
texture sampler types 'gsampler2DMS' and 'gsampler2DMSArray'. Do not
introduce overloads of sparseTexture*EXT, texture*ClampEXT or
sparseTexelFetchEXT for these sampler types. Remove references to
TEXTURE_2D_MULTISAMPLE_ARRAY.
Dependencies on EXT_gpu_shader5 and OES_gpu_shader5
If implemented on OpenGL GLSL ES 3.1 and neither EXT_gpu_shader5 nor
OES_gpu_shader5 is supported, do not introduce
sparseTextureGatherOffsetsEXT.
Dependencies on EXT_depth_bounds_test
If EXT_depth_bounds_test is not supported, references to the depth bounds
test should be removed.
Dependencies on NV_gpu_program4 and NV_gpu_program5
Modify Section 2.X.2, Program Grammar
<opModifier> ::= "SPARSE"
| "LODCLAMP"
<ccMaskRule> ::= "RESIDENT"
| "NONRESIDENT"
Modify Section 2.X.3.7, Program Condition Code Registers
(modify the first paragraph)
There are two general-purpose four-component condition code registers (CC0
and CC1), where each component of this register is a collection of
single-bit flags, including a sign flag (SF), a zero flag (ZF), an
overflow flag (OF), and a carry flag (CF). The values of these registers
are undefined at the beginning of program execution. Additionally, there
is a special single-component sparse memory condition code register that
holds the status of the most recently executed texture or image load
instruction using the "SPARSE" opcode modifier. This condition code
includes a resident flag (RESF) indicating whether all memory accessed by
the instruction was populated.
Modify Section 2.X.4.1, Program Instruction Modifiers
(Update the discussion of instruction precision modifiers. If
GL_NV_gpu_program_fp64 is not found in the extension string, the "F64"
instruction modifier described below is not supported.)
(add to Table X.14 of the NV_gpu_program4 specification.)
Modifier Description
-------- ------------------------------------------------------
SPARSE Update the sparse memory condition code with status on
whether the memory accessed by a texture or image load
instruction was fully populated.
LODCLAMP Clamp the LOD used by texture lookups to a specified
value
For texture fetch, surface load, and surface atomic instructions, the
"SPARSE" modifier specifies that the sparse memory condition code
described in Section 2.X.3.7 should be updated to reflect whether the
memory accessed by the instruction was fully populated.
For texture fetch instructions with implicit LOD calcuations (TEX, TXB,
TXD), the "LODCLAMP" modifier specifies that the instruction includes an
extra floating-point component indicating a minimum level of detail to be
used for the texture lookup. If the implicitly computed level of detail
is less than the level of detail provided in the instruction data, that
level should be used instead.
Modify Section 2.X.4.3, Program Destination Variable Update
(add to Table X.16, Condition Code Tests)
mask rule test name condition
--------------- ---------------------- -----------------
RESIDENT sparse resident RESF
NONRESIDENT sparse nonresident !RESF
(also modify the table description)
Table X.16, Condition Code Tests. The allowed rules are specified in
the "mask rule" column. For "RESIDENT" or "NONRESIDENT", all four
components of the test result are loaded from the RESF flag of the
sparse condition code. Otherwise, If "0" or "1" is appended ...
(modify the paragraph about condition code updates)
A program instruction can also optionally update one of the two general
condition code registers ...
(add a new paragraph about updating CCSPARSE)
Additionally, a program instruction accessing memory can optionally update
the sparse memory condition code register if the "SPARSE" instruction
modifier is specified. If the memory accessed by the instruction was
fully populated, the resident flag (RESF) is set; otherwise, RESF is
cleared.
Modify Section 2.X.4.4, Program Texture Access
(modify the prototype of the TextureSample utility function, adding
<coord2> and removing <lod>)
result_t_vec
TextureSample(float_vec coord, float_vec coord2,
float_vec ddx, float_vec ddy, int_vec offset);
(modify the description of <coord> to add <coord2>)
<coord> and <coord2> are two four-component floating-point vectors from
which the (s,t,r) texture coordinates used for the texture access, the
layer used for array textures, and the reference value used for depth
comparisons (section 3.8.14) are extracted according to Table X.17. ...
(replace the paragraph discussing <lod>)
<ddx> and <ddy> specify partial derivatives (ds/dx, dt/dx, dr/dx, ds/dy,
dt/dy, and dr/dy) for the texture coordinates, and may be used for level
of detail calculations and to derive footprint shapes for anisotropic
texture filtering.
The level of detail used for the texture lookup is a function of the
texture instruction type, texture target, LODCLAMP qualifier, and the
inputs <ddx> and <ddy>. For TEX, TXB, TXD, and TXP instructions in a base
level of detail is computed based on the partial derivatives <ddx> and
<ddy>. For the TXB and TXL instruction, an additional level of detail
value is taken from the component in <coord> or <coord2> identified by the
first entry in the "lod" column of Table X.17. For TXB, this value is
added to the computed base level of detail; for TXL, it specifies the base
level of detail. After that, per-texture and per-texture unit LOD biases
are added to the level of detail. Finally, if the LODCLAMP opcode
modifier is specified, an LOD clamp value is extracted from <coord> or
<coord2> according to the second entry in the "lod" column of Table X.17.
The computed level of detail is clamped to be greater than or equal to
this LOD clamp value.
coordinates used
texTarget Texture Type s t r lay shd lod
---------------- --------------------- ----- --- --- -----
1D TEXTURE_1D x - - - - w,x2
2D TEXTURE_2D x y - - - w,x2
3D TEXTURE_3D x y z - - w,x2
CUBE TEXTURE_CUBE_MAP x y z - - w,x2
RECT TEXTURE_RECTANGLE_ARB x y - - - -,-
ARRAY1D TEXTURE_1D_ARRAY_EXT x - - y - w,x2
ARRAY2D TEXTURE_2D_ARRAY_EXT x y - z - w,x2
ARRAYCUBE TEXTURE_CUBE_MAP_ARRAY x y z w - x2,y2
SHADOW1D TEXTURE_1D x - - - z w,x2
SHADOW2D TEXTURE_2D x y - - z w,x2
SHADOWRECT TEXTURE_RECTANGLE_ARB x y - - z -,-
SHADOWCUBE TEXTURE_CUBE_MAP x y z - w x2,y2
SHADOWARRAY1D TEXTURE_1D_ARRAY_EXT x - - y z w,x2
SHADOWARRAY2D TEXTURE_2D_ARRAY_EXT x y - z w -,x2
SHADOWARRAYCUBE TEXTURE_CUBE_MAP_ARRAY x y z w x2 -,y2
BUFFER TEXTURE_BUFFER_EXT <not supported>
RENDERBUFFER TEXTURE_RENDERBUFFER <not supported>
2DMS TEXTURE_2D_MULTISAMPLE <not supported>
ARRAY2DMS TEXTURE_2D_MULTISAMPLE_ <not supported>
ARRAY
Table X.17: Texture types accessed for each of the <texTarget>, and
coordinate mappings. Components "x", "y", "z", and "w" are taken from
the first coordinate vector <coord>; "x2" and "y2" are taken from the
second vector <coord2>. The "SHADOW" and "ARRAY" targets are special
pseudo-targets described below. The "coordinates used" column indicate
the input values used for each coordinate of the texture lookup, the
layer selector for array textures, the reference value for texture
comparisons, and up to two components of level-of-detail information.
Buffer textures are not supported by normal texture lookup functions,
but are supported by TXF and TXQ, described below. Renderbuffer and
multisample textures are not supported by normal texture lookup
functions, but are supported by TXFMS. The TXB and TXL instructions are
not supported for the targets SHADOWARRAY2D and SHADOWARRAYCUBE, so the
first column of "lod" is ignored.
Modify Section 2.X.8.Z, TXD: Texture Sample with Partials
... The partial derivatives of the texture coordinates with respect to X
and Y are specified by the second and third floating-point source vectors.
If the LODCLAMP instruction modifier is specified, floating-point
level-of-detail clamp value is specified in the <w> component of the third
floating-point source vector. The level of detail is computed
automatically using the provided partial derivatives.
Issues
(1) How does this extension compare to the ARB_sparse_texture extension?
RESOLVED: We extend the mechanisms provided by ARB_sparse_texture in
several ways:
- We add built-in texture and image lookup functions returning
information on memory accesses performed by the built-in functions;
in particular, whether any uncommitted memory was referenced.
- We add built-in texture and image lookup functions clamping the
final level of detail computed based on texture coordinates,
derivatives, and LOD bias to a minimum LOD specified in the shader.
- We specify that all loads and atomics from uncommitted sparse memory
behave as though zero were fetched.
- We remove the requirement that the base size of a sparse texture
must be a multiple of the page size. Implementations are expected
to pad mipmap allocations internally to page size boundaries as
required, until the tail is reached.
- We modify the definition of the sparse texture mipmap tail, so that
all levels greater than or equal to the page size in all dimensions
are guaranteed to be sparsely populated (i.e., not in the tail).
The previous spec allowed implementations to put levels in the tail
if they were not integer multiples of the page size.
- We add support for an implementation-independent virtual page size
for some formats, instead of depending on querying
implementation-dependent page size. For such formats, the default
virtual page size index (0) is guaranteed to specify the standard
page size.
- We require that all implementations of this extension return TRUE
for the value of the implementation-dependent constant
SPARSE_TEXTURE_FULL_ARRAY_CUBE_MIPMAPS_ARB, which removes some
potential errors when allocating sparse array or cube map textures.
- We add support for sparse multisample and multisample array
textures, but require no implementation-independent virtual page
size.
(2) How does this extension compare to the AMD_sparse_texture extension?
RESOLVED: This extension, like the AMD extension, provide built-in
texture lookup functions returning information on whether uncommitted
memory was accessed. There are several differences between these
functions:
- This extension uses an "EXT" suffix on built-in function names.
- This extension provides built-in functions supporting the sparse
return information together with the new LOD clamp feature.
- This extension supports sparse accesses for shadow map sampler types
(e.g., sampler2DShadow).
- This extension supports sparse variants of imageLoad(); the AMD
extension does not.
- This extension doesn't attempt to support sparse variants of
projective texture lookups to reduce the number of texture functions
added.
- This extension doesn't attempt to support sparse variants of
one-dimensional and one-dimensional array texture lookups. Sparse
textures with these targets are explicitly not supported in the ARB
extension.
- This extension returns the texel data in an "out" parameter and
returns a value consistent with sampling zero in any uncommitted
texels. The AMD extension returns the texel data in an "inout"
parameter and guarantees not to write to the return value if any
uncommitted texel is accessed.
- The function sparseTexelResident() from the AMD extension is renamed
to sparseTexelsResidentEXT(). We use "texels" instead of "texel" in
the function name because a texture lookup may access multiple
texels, and the code will reflect non-resident status if any of the
texels is non-resident.
The built-in functions taking an explicit LOD clamp, returning zero on
reads from uncommitted memory, and the standard virtual page size are
not provided by the AMD extension, either.
Neither this extension nor ARB_sparse_texture provide the minimum LOD
warning feature provided by the AMD extension or the related built-in
functions.
(3) How should the "sparse" built-in functions return both access status
and a texel value?
RESOLVED: We mostly followed the precedent of the AMD extension, where
the sparse access status is returned as an integer and the texel values
are returning in a vec4-typed "out" parameter. (This differs slightly
from the AMD extension in that it uses an "inout" parameter.)
We considered included returning the texel values from the function,
just like normal texture lookups, and returning status in a separate
"out" parameter (reversing the order). We also considered returning a
structure type containing both the status and the texel. We ultimately
chose to return the status code to more closely match the AMD extension
and because we expect that shaders caring to use the "sparse" functions
will want to look at the status code first.
(4) What data type should we use for the access status information
returned by the "sparse" built-in functions?
RESOLVED: We chose to follow the precedent of the AMD extension, where
an integer code is returned. Requiring a separate function call
(sparseTexelsResidentEXT) is required to reason about the code returned
is mildly annoying, but we didn't consider it serious enough to warrant
a change.
We could have used a "bool" type instead, but chose to stick with "int"
for compatibility and for possible future expansion. The AMD extension
also includes built-in functions sparseTexelMinLodWarning() and
sparseTexelWarningFetch() that can be used to check the return code for
other conditions not supported by this extension. Shaders that only
care about residency information can still check the status in a single
(long) line:
if (!sparseTexelsResidentEXT(sparseTextureEXT(sampler, coords,
texel))
{
// do something about the failure
}
(5) When using a "sparse" built-in texture function, what RGBA values are
generated when the lookup accesses one or more uncommited texels?
RESOLVED: We return a filtered result vector where memory for
uncommitted texels is treated as being filled with zeroes. The data
vector returned by the "sparse" functions for this case should exactly
match the vector returned by an equivalent non-"sparse" function.
(6) For "sparse" built-in texture functions, where should the <texel>
return value go relative to other parameters?
RESOLVED: We chose to follow the precedent of the AMD extension,
putting it in (approximately) the last parameter. Note that the
optional <bias> parameter of texture() breaks this pattern; we chose to
keep the optional bias at the end.
Other options considered included: always first (before the sampler),
always second (after the sampler), always third (after the sampler and
the base coordinates). For "always third", note there are a couple
cases like shadow lookups in cube arrays where the coordinates are split
across multiple parameters and "always third" would be awkward.
Additional options are discussed in issue (3).
(7) Should we provide sparse variants of the "2DMS" and "2DMSArray"
variants of texelFetch() and imageLoad() in this extension?
RESOLVED: Yes. ARB_sparse_texture doesn't support multisample
textures. In this extension, we lift this restriction, allow them to be
accessed using normal built-ins, and provide new functions allowing
shaders to determine if uncommitted memory was accessed.
(8) How does the feedback provided in the "sparse" built-in texture
functions interact with texture filtering modes involving multiple
texels?
RESOLVED: The sparse texture lookup status will indicate that
uncommitted memory was accessed if any texel read during the filtering
operation was uncommitted, but will do so only if the filter weight is
non-zero. When applying a texture filter such as LINEAR_MIPMAP_LINEAR,
it's possible that the interpolated texture coordinate lines up exactly
at the center of a texel and/or exactly at an integer level of detail.
According to the standard filtering equations, eight samples are taken
-- four in each of two levels. However, it's possible that only one of
the eight samples has a non-zero weight (if the coordinates hit a texel
center and the LOD is an integer).
This "non-zero weight" feature may be important for getting proper
feedback in some cases, such as displaying a texture tile with an
aligned 1:1 mapping of pixels to texels or forcing a specific level of
detail in some cases. Note that when attempting to apply a 1:1 mapping
of pixels to texels via an interpolated texture attribute, it's possible
that small floating-point errors might produce very small but non-zero
weights for neighboring texels. If avoiding such errors is important
and a 1:1 mapping is required, a single-sample filter like NEAREST
should be used.
(9) Should we support sparse texel fetches and image loads for buffer
textures?
RESOLVED: Not in this extension. This should be handled by a separate
extension allowing for the creation and use of sparse buffer resources.
Such an extension might also provide the ability to get "sparse"
information when non-texture mechanisms are used to access memory (e.g.,
ARB_shader_storage_buffer_object, NV_shader_buffer_load).
(10) Should we support "sparse" variants of the image atomic functions
that return information on residency as well as the value normally
returned by the atomic operation?
RESOLVED: Not in this extension; it's not clear that there's an
important use case for this. If required, a shader can use imageLoad()
to probe the residency of a given texel and ignore the data values
returned.
(11) This extension is adding a *large* number of new built-in functions.
What can we do to control this?
RESOLVED: We chose not to add any "sparse" or "LOD clamp" variants of
projective texture lookups (e.g., textureProj). If required, you can
divide through by the "q" texture coordinate and use an equivalent
non-projective lookup.
We obviously don't support features that make no sense -- for example,
LOD clamp on single-level rectangle textures.
We considered the possibility of more significant GLSL syntax changes to
reduce the cross-product of different features. For example, the AMD
extension has a function:
int sparseTextureProjGradOffset(...);
that combines four separate "optional" features (sparse, projection,
explicitly specified gradients, and texel offsets) and is supported for
six separate texture targets. One might consider an approach like:
#define TEX_IS_PROJECTIVE 0x1
#define TEX_HAS_GRADIENTS 0x2
#define TEX_HAS_TEXEL_OFFSET 0x4
#define TEX_WANTS_SPARSE_STATUS 0x8
struct TexLookup3D {
uint flags; /* in */
float q; /* in */
vec3 ddx, ddy; /* in */
ivec3 texelOffset; /* in */
int sparseStatus; /* out */
};
...
TexLookup3D lookup;
lookup.flags = (TEX_IS_PROJECTIVE | TEX_HAS_GRADIENTS |
TEX_HAS_TEXEL_OFFSET | TEX_WANTS_SPARSE_STATUS);
lookup.q = coords.w;
lookup.ddx = ddx;
lookup.ddy = ddy;
lookup.texelOffset = ivec3(-1,+1,+2);
texture(sampler, lookup);
to handle all possible cases in one interface. Alternately, a
"prettier" C++-style approach with methods on sampler classes could be
used.
Given that either such feature might involve a large change to the
shading language, it seems more appropriate to address this issue in a
future core version of a shading language rather than an extension.
(12) For new "LOD clamp" functions, how does the LOD clamp interact with
the LOD bias?
RESOLVED: The LOD clamp is applied after the LOD bias. Clamping to the
LOD provided in the shader is logically applied at the same point in the
pipeline where the LOD clamps based on the texture/sampler parameters
TEXTURE_{MIN,MAX}_LOD are applied.
(13) How does the "reads produce zero" behave if a sparse texture is bound
to a framebuffer and used for the depth or stencil test?
RESOLVED: The depth and stencil tests act as though zero were read from
the framebuffer. The actual results of the tests depend on the depth
and stencil functions, the incoming depth value, and the stencil
reference value.
There may be cases where it might be advantageous to configure the depth
or stencil tests to fail when touching an unpopulated portion of the
depth/stencil buffer. The "return zero" behavior may work well for some
cases (e.g., returning zero when using a depth test of LESS will cause
the test to almost always fail), but not as well for others (e.g., depth
test of GREATER). We've chosen not to address this case in the current
extension.
(14) How does the "reads produce zero" behave for textures that don't have
all four components?
RESOLVED: Components that are present in the texture will return zero;
others will return default values. For example, an access to an
uncommitted sparse texture whose with a format has no alpha component
(e.g, RGB8) will return 1.0 on the alpha channel of the returned RGBA
vector. The handling of "missing" components is the same as for
non-sparse textures.
(15) Should we provide standard sparse texture page sizes that
applications can rely on without having to query the set of supported
page sizes for each format it uses? If so, how will this be handled?
Will we have some formats that have standard sizes and others that
don't?
RESOLVED: Yes; we will provide standard page sizes for some, but not
all, formats. However, we will still allow for implementation-
dependent page sizes (as in ARB_sparse_textures) for formats that have a
standard page size and allow implementations to support sparse textures
on formats for which a standard page size is not available. The basic
page sizes we use arrange sparse textures into 64KB pages and attempt to
keep the X, Y, and Z (for 3D) dimensions of the page roughly equal.
(16) Should we add specific compressed formats to the required formats list
and provide standard page sizes?
RESOLVED: Not in this extension. Note that the current
ARB_sparse_texture extension already allows implementations to support
compressed formats.
We've chosen not to go to the trouble of enumerating standard page sizes
for all the compressed formats (many of which are added by extension),
but one logical approach would be to treat each 64- or 128-bit block in
common formats as a single logical texel and treat the standard page
sizes of 64- and 128-bit texels as being in units of compression blocks.
(17) How do applications get to use the standard page size?
RESOLVED: Applications opt in to using standard page sizes by leaving
VIRTUAL_PAGE_SIZE_INDEX_ARB at its initial value (zero).
In ARB_sparse_texture, there were no standard page sizes. Applications
can use GetInternalformativ() with <pname> of NUM_VIRTUAL_PAGE_SIZES_ARB
to query the implementation-dependent number of page sizes supported for
any given format. Some formats may be unsupported, and the GL will
return a page size count of zero. Other formats may have a page size
count of one, or more than one if the implementation supports multiple
page sizes. An application can query the properties of each page size
index by calling GetInternalFormativ() with <pname> set to
VIRTUAL_PAGE_SIZE_{X,Y,Z}_ARB. When an application determines the page
size it wants to use from the options returned by the GL, it sets the
VIRTUAL_PAGE_SIZE_INDEX_ARB texture parameter prior to calling
TexStorage* to allocate storage for the sparse texture.
If an application doesn't bother setting the VIRTUAL_PAGE_SIZE_INDEX_ARB
texture parameter, the default index of zero will be used and the page
size will be whatever the implementation chooses for its first page size
index. In the absence of this extension, the application still needs to
call GetInternalFormativ() to determine the page size being used so it
can manage texture residency. But in the presence of this extension, page
size index 0 will be a standard size and will be the same on all
implementations supporting the extension.
(18) Should we support sparse multisample textures? If so, should we
support standard virtual page sizes?
RESOLVED: Yes, we add will support for sparse multisample textures, but
will not specify standard page sizes.
Different implementations of this extension may represent multisample
textures in different ways. Some implementations might interleave
samples in memory, while others might have separate "planes" in memory
for each individual sample. If we were to support a standard page size,
the easiest approach might be to have a greatest-common-multiple
standard page size. For example, the standard page size for
single-sample textures with 32-bit texels is 128x128 (64KB total). We
could choose to use the same page size for multisample textures. For 4x
multisample, a page of 128x128 pixels would have an effective page size
of 256KB. If an implementation interleaves samples, each virtual page
might be assembled from four consecutive 64K physical pages. If an
implementation has separate "planes", the virtual page might be
assembled from four 64K physical pages spread out in memory.
(19) Should we require support for sparse depth or stencil textures?
Sparse support for these formats is optional in ARB_sparse_texture.
If so, should we support standard virtual page sizes?
RESOLVED: Not in this extension.
The current ARB_sparse_texture extension already allows implementations
to support sparse depth/stencil formats, so the only things a change
could accomplish is (a) provide standard page sizes that can be used
without querying implementation page sizes, (b) ensure that apps can
rely on *some* support by just checking the extension without querying
the number of supported page sizes via GetInternalFormat.
We expect that different implementations may store depth and stencil
textures in different ways and might have different "natural" page
sizes. We could deal with this by using a greatest-common-multiple
standard page size (i.e., have a standard page size larger than 64K),
but it's not clear if that will fly.
The advantages of (b) seem low relative to (a), so we aren't proposing
to add depth and stencil formats to the required list for this
extension.
(20) Should we make a separate extension for the LOD clamp GLSL functions?
RESOLVED: No. While the LOD clamp function doesn't have any real
interaction with sparse textures, its intent is to force the use of a
coarser level of detail that is known (or suspected) to be populated.
We expect that applications using sparse textures may make some of the
coarser levels of detail fully resident, but make portions finer levels
of detail resident selectively. Without using the feedback mechanism
(from the sparseTexture*) functions or without being able to have
portions of the texture non-resident, the LOD clamp built-ins don't
really make much sense.
(21) Should we reconsider re-examining some of the non-orthogonalities in
the current set of texture built-ins, which are being extended for
sparse. For example, the texture() built-in for a sampler type of
samplerCubeArrayShadow does not include an optional LOD bias despite
the fact that cubemap arrays do support multiple LODs.
RESOLVED: Not in this extension.
We chose to create "sparse" variants of existing built-ins without
re-examining current capabilities. It might make sense to have an
extension or future core shading language re-examine things and improve
orthogonality if implementations can support it.
Revision History
Revision 1
- Internal revisions
Revision 2 - December 18, 2014 - mheyer
- added ES 3.1 interactions
Revision 3 - April 19, 2016 - dkoch
- fix typos, add interactions with OES extensions