skia / external / github.com / KhronosGroup / OpenGL-Registry / 6bd92218f5ab5ee6c9fd02c0993dcae3ebb5c063 / . / extensions / SGIX / SGIX_texture_phase.txt

XXX - Not complete yet!!! | |

Name | |

SGIX_texture_phase | |

Name Strings | |

GL_SGIX_texture_phase | |

Version | |

$Date: 1997/12/08 19:59:59 $ $Revision: 1.3 $ | |

Number | |

?? | |

Dependencies | |

None | |

Overview | |

This extension allows textures to filtered using a modified LINEAR | |

filter that treats the texture data as phase angle. (In addition | |

to the NEAREST and LINEAR filters defined in the original GL | |

Specification.) Such filtering is useful for dopler data where | |

texel values correspond to positions on a unit circle or phase | |

angles. | |

Issues | |

* | |

Reasoning | |

* | |

New Procedures and Functions | |

None | |

New Tokens | |

Accepted by the <param> parameter of TexParameteri and | |

TexParameterf, and by the <params> parameter of TexParameteriv and | |

TexParameterfv, when their <pname> parameter is | |

TEXTURE_MIN_FILTER or TEXTURE_MAG_FILTER: | |

PHASE_SGIX 0x832A | |

Additions to Chapter 2 of the GL Specification (OpenGL Operation) | |

None | |

Additions to Chapter 3 of the GL Specification (Rasterization) | |

The additional token value PHASE_SGIS is accepted as an enumerated | |

value for the texture minification and magnification filters, causing | |

Table 3.7 to be replaced with the table below: | |

Name Type Legal Values | |

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

TEXTURE_WRAP_S integer CLAMP, REPEAT | |

TEXTURE_WRAP_T integer CLAMP, REPEAT | |

TEXTURE_WRAP_R_EXT integer CLAMP, REPEAT | |

TEXTURE_MIN_FILTER integer NEAREST, LINEAR, | |

NEAREST_MIPMAP_NEAREST, | |

NEAREST_MIPMAP_LINEAR, | |

LINEAR_MIPMAP_NEAREST, | |

LINEAR_MIPMAP_LINEAR, | |

FILTER4_SGIS, | |

PHASE_SGIS | |

TEXTURE_MAG_FILTER integer NEAREST, LINEAR, | |

FILTER4_SGIS, | |

PHASE_SGIX | |

TEXTURE_BORDER_COLOR 4 floats any 4 values in [0,1] | |

Table 3.7: Texture parameters and their values. | |

Phase filtering is specified by calling TexParameteri, | |

TexParameterf, TexParameteriv, or TexParameterfv with <pname> set | |

to TEXTURE_MIN_FILTER or TEXTURE_MAG_FILTER, and <param> or <params> | |

set to PHASE_SGIS. Because phase filtering is defined only for | |

non-mipmapped textures, there is no difference between its | |

definition for minification and magnification. | |

First consider the 1-dimensional case. Let T be a computed texture | |

value (one of R_t, G_t, B_t, or A_t). Let T[i] be the component | |

value of the texel at location i in a 1-dimensional texture image. | |

Then, if the appropriate texture filter mode is PHASE_SGIX, a | |

2-texel group is selected: | |

/ floor(u - 1/2) mod 2**n, TEXTURE_WRAP_S is REPEAT | |

i0 = ( | |

\ floor(u - 1/2), TEXTURE_WRAP_S is CLAMP | |

/ (i0 + 1) mod 2**n, TEXTURE_WRAP_S is REPEAT | |

i1 = ( | |

\ i0 + 1, TEXTURE_WRAP_S is CLAMP | |

Let | |

A = frac(u - 1/2) | |

where frac(x) denotes the fractional part of x, and u is the | |

texture image coordinate in the s direction, as illustrated in | |

Figure 3.10 of the GL Specification. Then the texture value T is | |

found as: | |

t0 = T[i0] | |

t1 = T[i1] | |

del = t1 - t0 | |

if |del| > 0.5 then | |

t0 = t0 + sign(del) | |

T = frac((1-A) * t0 + A * t1) | |

If any of the selected T[i] in the above equation refer to a border | |

texel with unspecified value, then the border color given by the | |

current setting of TEXTURE_BORDER_COLOR is used instead of the | |

unspecified value. | |

For 2-dimensional textures the calculations for i0, i1, and | |

A are identical to the 1-dimensional case. A 4-texel group is | |

selected, requiring two j values computed as | |

/ floor(v - 1/2) mod 2**m, TEXTURE_WRAP_T is REPEAT | |

j0 = ( | |

\ floor(v - 1/2), TEXTURE_WRAP_T is CLAMP | |

/ (j0 + 1) mod 2**m, TEXTURE_WRAP_T is REPEAT | |

j1 = ( | |

\ j0 + 1, TEXTURE_WRAP_T is CLAMP | |

Let | |

B = frac(v - 1/2) | |

where v is the texture image coordinate in the t direction, as | |

illustrated in Figure 3.10 of the GL Specification. Then the | |

texture value T is found as: | |

t00 = T[i0,j0] | |

t01 = T[i0,j1] | |

t10 = T[i1,j0] | |

t11 = T[i1,j1] | |

del = t10 - t00 | |

if |del| > 0.5 then | |

t00 = t00 + sign(del) | |

t0 = frac((1-A) * t00 + A * t10) | |

del = t11 - t01 | |

if |del| > 0.5 then | |

t01 = t01 + sign(del) | |

t1 = frac((1-A) * t01 + A * t11) | |

del = t1 - t0 | |

if |del| > 0.5 then | |

t0 = t0 + sign(del) | |

T = frac((1-A) * t0 + A * t1) | |

If any of the selected T[i,j] in the above equation refer to a | |

border texel with unspecified value, then the border color given by | |

the current setting of TEXTURE_BORDER_COLOR is used instead of the | |

unspecified value. | |

Phase texture filtering is similarly defined for 3-dimensional | |

textures. | |

Additions to Chapter 4 of the GL Specification (Per-Fragment Operations | |

and the Framebuffer) | |

None | |

Additions to Chapter 5 of the GL Specification (Special Functions) | |

None | |

Additions to Chapter 6 of the GL Specification (State and State Requests) | |

None | |

Additions to the GLX Specification | |

None | |

GLX Protocol | |

Errors | |

New State | |

New Implementation Dependent State | |