skia / external / github.com / KhronosGroup / OpenGL-Registry / 4a8ee5dd31809d8f1318933804b6842c37a3b644 / . / extensions / EXT / EXT_texture_filter_minmax.txt

Name | |

EXT_texture_filter_minmax | |

Name Strings | |

GL_EXT_texture_filter_minmax | |

Contact | |

Pat Brown, NVIDIA Corporation (pbrown 'at' nvidia.com) | |

Contributors | |

Jeff Bolz, NVIDIA Corporation | |

Mark Kilgard, NVIDIA Corporation | |

Eric Werness, NVIDIA Corporation | |

James Helferty, NVIDIA Corporation | |

Daniel Koch, NVIDIA Corporation | |

Status | |

Shipping | |

Version | |

Last Modified Date: March 27, 2015 | |

Revision: 2 | |

Number | |

OpenGL Extension #464 | |

OpenGL ES Extension #227 | |

Dependencies | |

This extension is written against the OpenGL 4.3 Specification | |

(Compatibility Profile), dated February 14, 2013. | |

OpenGL 1.0 is required. | |

This extension interacts with EXT_texture_filter_anisotropic. | |

This extension interacts with EXT_direct_state_access. | |

This extension interacts with OpenGL ES 3.1 (June 4, 2014). | |

When implemented for OpenGL ES 3.1, this extension interacts with | |

EXT_texture_border_clamp. | |

When implemented for OpenGL ES 3.1, this extension interacts with | |

OES_texture_stencil8. | |

Overview | |

In unextended OpenGL 4.3, minification and magnification filters such as | |

LINEAR allow texture lookups to returned a filtered texel value produced | |

by computing an weighted average of a collection of texels in the | |

neighborhood of the texture coordinate provided. | |

This extension provides a new texture and sampler parameter | |

(TEXTURE_REDUCTION_MODE_EXT) which allows applications to produce a | |

filtered texel value by computing a component-wise minimum (MIN) or | |

maximum (MAX) of the texels that would normally be averaged. The | |

reduction mode is orthogonal to the minification and magnification filter | |

parameters. The filter parameters are used to identify the set of texels | |

used to produce a final filtered value; the reduction mode identifies how | |

these texels are combined. | |

New Procedures and Functions | |

None. | |

New Tokens | |

Accepted by the <pname> parameter to SamplerParameter{i f}{v}, | |

SamplerParameterI{u}iv, GetSamplerParameter{i f}v, | |

GetSamplerParameterI{u}iv, TexParameter{i f}{v}, TexParameterI{u}iv, | |

GetTexParameter{i f}v, GetTexParameterI{u}iv, TextureParameter{i f}{v}EXT, | |

TextureParameterI{u}ivEXT, GetTextureParameter{i f}vEXT, | |

GetTextureParameterI{u}ivEXT, MultiTexParameter{i f}{v}EXT, | |

MultiTexParameterI{u}ivEXT, GetMultiTexParameter{i f}vEXT, and | |

GetMultiTexParameterI{u}ivEXT: | |

TEXTURE_REDUCTION_MODE_EXT 0x9366 | |

Accepted by the <param> or <params> parameter to SamplerParameter{i f}{v}, | |

SamplerParameterI{u}iv, TexParameter{i f}{v}, TexParameterI{u}iv, | |

TextureParameter{i f}{v}EXT, TextureParameterI{u}ivEXT, | |

MultiTexParameter{i f}{v}EXT, or MultiTexParameterI{u}ivEXT when <pname> | |

is TEXTURE_REDUCTION_MODE_EXT: | |

WEIGHTED_AVERAGE_EXT 0x9367 | |

MIN (reused from core) | |

MAX (reused from core) | |

Modifications to the OpenGL 4.3 Specification (Compatibility Profile) | |

Modify Section 8.10, Texture Parameters (p. 241) | |

(add to Table 8.24, pp. 241-243) | |

Name Type Legal Values | |

-------------------------- ---- -------------------- | |

TEXTURE_REDUCTION_MODE_EXT enum WEIGHTED_AVERAGE_EXT, | |

MIN, MAX | |

Modify Section 8.14.2, Coordinate Wrapping and Texel Selection (p. 254) | |

(add below the equations specifying the values i_0, j_0, ... beta, gamma) | |

... where frac(x) denotes the fractional part of <x> and may be quantized | |

to a fixed-point value with implementation-dependent precision. | |

Modify Section 8.14.3, Mipmapping (p. 259) | |

(modify the last paragraph in the section, p. 261) | |

The final texture value is then found as: | |

tau = (1 - frac(lambda)) * tau_1 + frac(lambda) * tau_2, | |

where frac(x) denotes the fractional part of <x> and may be quantized to a | |

fixed-point value with implementation-dependent precision. | |

Modify Section 8.17, Texture Completeness (p. 263) | |

(modify the last two bullets in the section, p. 264) | |

* The internal format of the texture arrays is integer (see tables 8.19- | |

8.20), the texture reduction mode is WEIGHTED_AVERAGE_EXT, and either | |

the magnification filter is not NEAREST, or the minification filter is | |

neither NEAREST nor NEAREST_MIPMAP_NEAREST. | |

* The internal format of the texture is DEPTH_STENCIL, the DEPTH_- | |

STENCIL_TEXTURE_MODE for the texture is STENCIL_INDEX, the texture | |

reduction mode is WEIGHTED_AVERAGE_EXT, and either the magnification | |

filter or the minification filter is not NEAREST. | |

Insert before Section 8.23, sRGB Texture Color Conversion (p. 279) | |

Section 8.X, Texture Reduction Modes | |

When using minification and magnification filters such as LINEAR, or when | |

using anisotropic texture filtering, the values of multiple texels will | |

normally be combined using a weighted average to produce a filtered | |

texture value. However, a filtered texture value may also be produced by | |

computing per-component minimum and maximum values over the set of texels | |

that would normally be averaged. The texture and sampler parameter | |

TEXTURE_REDUCTION_MODE_EXT controls the process by which multiple texels | |

are combined to produce a filtered texture value. When set to its default | |

state of WEIGHTED_AVERAGE_EXT, a weighted average will be computed, as | |

described in previous sections. | |

When TEXTURE_REDUCTION_MODE_EXT is MIN or MAX, the equations to produce a | |

filtered texel value for LINEAR minification or magnification filters | |

(equation 8.10 and subsequent unnumbered ones) are replaced with | |

tau = reduce((1-alpha)*(1-beta)*(1-gamma), tau_i0_j0_k0, | |

( alpha)*(1-beta)*(1-gamma), tau_i1_j0_k0, | |

(1-alpha)*( beta)*(1-gamma), tau_i0_j1_k0, | |

( alpha)*( beta)*(1-gamma), tau_i1_j1_k0, | |

(1-alpha)*(1-beta)*( gamma), tau_i0_j0_k1, | |

( alpha)*(1-beta)*( gamma), tau_i1_j0_k1, | |

(1-alpha)*( beta)*( gamma), tau_i0_j1_k1, | |

( alpha)*( beta)*( gamma), tau_i1_j1_k1), | |

tau = reduce((1-alpha)*(1-beta), tau_i0_j0, | |

( alpha)*(1-beta), tau_i1_j0, | |

(1-alpha)*( beta), tau_i0_j1, | |

( alpha)*( beta), tau_i1_j1), or | |

tau = reduce((1-alpha), tau_i0, | |

( alpha), tau_i1) | |

for three-, two-, and one-dimensional texture accesses, respectively. The | |

function reduce() is defined to operate on pairs of weights and texel | |

values. If the reduction mode is MIN or MAX, reduce() computes a | |

component-wise minimum or maximum, respectively, of the R, G, B, and A | |

components of the set of provided texels with non-zero weights. | |

For minification filters involving two texture levels | |

(NEAREST_MIPMAP_LINEAR and LINEAR_MIPMAP_LINEAR), filtered values for the | |

two selected levels, tau_1 and tau_2, are produced as described in section | |

8.14.3, but using the reductions described immediately above. The two | |

filtered values will be combined to generate a final result using the | |

equation | |

tau = reduce((1-frac(lambda)), tau_1, | |

( frac(lambda)), tau_2), | |

where tau_1 and tau_2 are filtered values for levels d_1 and d_2, and | |

frac(lambda) is the fractional portion of the texture level of detail and | |

may be quantized to a fixed-point value with implementation-dependent | |

precision. | |

If anisotropic texture filtering is enabled, a reduction mode of | |

WEIGHTED_AVERAGE_EXT will produce a filtered texel value by computing a | |

weighted average of texel values, using an implementation-dependent set of | |

selected texels and weights. When using reduction modes of MIN or MAX, a | |

filtered texel value will be produced using the equation | |

tau = reduce(tau_1, ..., tau_N) | |

where tau_1 through tau_N are the <N> texels that would be used with | |

non-zero weights when a reduction mode of WEIGHTED_AVERAGE_EXT is used. | |

If a texture access using a reduction mode of MIN or MAX is used with a | |

texture access with depth comparisons enabled (section 8.22.1), the | |

individual tau values used in the reduce() functions should reflect the | |

results of the depth comparison (0.0 or 1.0), not the original values in | |

the depth texture. | |

Additions to the AGL/GLX/WGL Specifications | |

None. | |

Errors | |

INVALID_ENUM is generated when SamplerParameter*, TexParameter*, | |

TextureParameter*EXT, and MultiTextureParameter*EXT is called with a | |

<pname> of TEXTURE_REDUCTION_MODE_EXT and a <param> value or value pointed | |

to by <params> points that is not one of WEIGHTED_AVERAGE_EXT, MIN, or | |

MAX. | |

New State | |

Add to Table 23.23, Textures (state per sampler object) | |

Initial | |

Get Value Type Get Command Value Description Sec. | |

-------------------------- ---- ------------ --------- ------------------------ ----- | |

TEXTURE_REDUCTION_MODE_EXT E GetTexParam- WEIGHTED_ Texture reduction mode 8.10 | |

eteriv AVERAGE_EXT (average, minimum, maximum) | |

New Implementation Dependent State | |

None. | |

Dependencies on EXT_texture_filter_anisotropic | |

If EXT_texture_filter_anisotropic is not supported, references to | |

anisotropic filtering in the discussion of texture reduction modes should | |

be removed. | |

Dependencies on EXT_direct_state_access | |

If EXT_direct_state_access is not supported, references to these functions | |

should be removed: | |

TextureParameter{i f}{v}EXT, TextureParameterI{u}ivEXT, | |

GetTextureParameter{i f}vEXT, GetTextureParameterI{u}ivEXT, | |

MultiTexParameter{i f}{v}EXEXTT, MultiTexParameterI{u}ivEXT, | |

GetMultiTexParameter{i f}vEXT, and GetMultiTexParameterI{u}ivEXT | |

Interactions with EXT_texture_border_clamp | |

References to each of the following functions should be decorated with the | |

EXT suffix: | |

SamplerParameterI{u}iv, GetSamplerParameterI{u}iv, | |

TexParameterI{u}iv, and GetTexParameterI{u}iv | |

If EXT_texture_border_clamp is not supported, all references to the above | |

functions should be removed. | |

Interactions with OpenGL ES 3.1 | |

Ignore any earlier changes to the "Texture Completeness" section. | |

In section 8.16 "Texture Completeness", Modify the last three bullets: | |

* The effective internal format specified for the texture arrays is a | |

sized internal color format that is not texture-filterable (see table | |

8.13), the texture reduction mode is WEIGHTED_AVERAGE_EXT, and either | |

the magnification filter is not NEAREST or the minification filter is | |

neither NEAREST nor NEAREST_MIPMAP_NEAREST. | |

* The effective internal format specified for the texture arrays is a | |

sized internal depth or depth and stencil format (see table 8.14), the | |

value of TEXTURE_COMPARE_MODE is NONE, the texture reduction mode is | |

WEIGHTED_AVERAGE_EXT, and either the magnification filter is not | |

NEAREST or the minification filter is neither NEAREST nor | |

NEAREST_MIPMAP_NEAREST. | |

* The internal format of the texture is DEPTH_STENCIL, the value of | |

DEPTH_STENCIL_TEXTURE_MODE for the texture is STENCIL_INDEX, the | |

texture reduction mode is WEIGHTED_AVERAGE_EXT, and either the | |

magnification filter or the minification filter is not NEAREST. | |

Interactions with OES_texture_stencil8 | |

Modify 3.8.13 "Texture Completeness" to change the bullet added by | |

OES_texture_stencil8 to the list of reasons a texture would be complete: | |

* The internal format of the texture is STENCIL_INDEX, the | |

TEXTURE_REDUCTION_MODE_EXT parameter is WEIGHTED_AVERAGE_EXT, and | |

either the magnification filter is not NEAREST or the minification | |

filter is neither NEAREST nor NEAREST_MIPMAP_NEAREST. | |

Issues | |

(1) What should this extension be called? | |

RESOLVED: EXT_texture_filter_minmax, as it allows for "min" and "max" | |

operations during texture filtering. This follows the precedent of | |

EXT_blend_minmax, which provides similar functionality for blending | |

values in the framebuffer. | |

(2) How does this extension interact with restrictions on min/mag filters | |

textures with integer components? | |

RESOLVED: In unextended OpenGL 4.3, a texture with integer components | |

(e.g., RGBA8I) is considered incomplete if used with minification or | |

magnification filters that normally average multiple samples (anything | |

other than NEAREST and NEAREST_MIPMAP_NEAREST). This restriction exists | |

to avoid the need to define semantics for computing a weighted average | |

of integer values with non-integer weights, which will produce an | |

arithmetic result that is not an integer. Given that the MIN and MAX | |

reduction modes don't do any arithmetic and won't produce non-integer | |

values, we allow these reduction modes to be used with arbitrary | |

filters. | |

(3) How does this extension interact with TEXTURE_COMPARE_MODE set | |

to COMPARE_R_TO_TEXTURE for depth textures? | |

RESOLVED: The per-sample comparison should be performed prior to the | |

min/max reduction. | |

This implies the MIN mode for TEXTURE_REDUCTION_MODE_EXT in this | |

case returns a false value if *any* of the texels compare false; to | |

return true, every comparison must be true. Likewise this implies | |

the MAX mode for TEXTURE_REDUCTION_MODE_EXT in this case returns | |

a true value if *any* of the texels compare true; to return false, | |

every comparison must be false. | |

Note that unextended OpenGL 4.3 doesn't actually require that linear | |

filtering actually average depth comparison results of 0.0 and 1.0, but | |

behaving this way appears to be common practice and may be required for | |

other 3D graphics APIs. | |

(4) Do interpolation weights figure into the min/max reductions? | |

RESOLVED: Yes. Texels that would have a weight of zero for the normal | |

WEIGHTED_AVERAGE_EXT reduction modes should not be considered when | |

performing MIN or MAX reductions. | |

Note that implementations may end up quantize the interpolation weights | |

to fixed-point values with implementation-dependent precision. This may | |

cause samples to be ignored in WEIGHTED_AVERAGE_EXT or MIN/MAX | |

reductions. For example, if you are using a minification filter of | |

LINEAR_MIPMAP_LINEAR and the computed LOD is 2.00001, the implementation | |

may round the LOD as being exactly 2.0 and ignore the texels in level 3 | |

for the purposes of trilinear filtering. | |

(5) Should TEXTURE_REDUCTION_MODE_EXT work with stencil textures? | |

RESOLVED: Yes. | |

Revision History | |

Revision 2, 2015/03/27 | |

- Add ES interactions | |

Revision 1 | |

- Internal revisions. |