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1Name
2
3    SGIX_fog_blend_alpha
4    SGIX_fog_blend_color
5
6Name Strings
7
8    GL_SGIX_fog_blend
9
10Version
11
12    $Date: 1997/09/15 19:26:36 $ $Revision: 1.3 $
13
14Number
15
16        ????
17
18Dependencies
19
20        XXX
21
22Overview
23
24    This extension affect the way the fog coefficient (f) is used to
25    blend the rasterized fragments in non-indexed color mode.
26    When enabled using the GL_FOG_BLEND_ALPHA_SGIX parameter,
27    the alpha component of the fog color is used to change the
28    resulting alpha, as well as the RGB components.
29    The color components may stay unchanged by the fog computation
30    if the GL_FOG_BLEND_COLOR_SGIX is disabled.
31    No change is done to the equation C = f*Cr + (1-f)Cf
32
33
34New Procedures and Functions
35
36    None
37
38New Tokens
39
40    Accepted by the <cap> parameter of Enable, Disable, and IsEnabled
41
42        GL_FOG_BLEND_ALPHA_SGIX		0x81FE
43        GL_FOG_BLEND_COLOR_SGIX		0x81FF
44
45Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
46
47    None
48
49Additions to Chapter 3 of the 1.0 Specification (Rasterization)
50
51
52    3.9 Fog
53
54    ... (The rasterized fragment's A value is not changed by fog blending.)...
55    is removed and replaced by.
56
57    The rasterized fragment alpha value is not changed by the fog blending,
58    unless specified otherwise by enabling it with the GL_FOG_BLEND_ALPHA_SGIX
59    parameter. Color modifications can be turned off by disabling with
60    the GL_FOG_BLEND_COLOR_SGIX paramater.
61
62
63
64Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
65and the Framebuffer)
66
67    None
68
69Additions to Chapter 5 of the 1.0 Specification (Special Functions)
70
71    None
72
73Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
74
75    Fog alpha blend enable/disable state is checked by calling glIsEnable
76    function with GL_FOG_BLEND_ALPHA_SGIX parameter.
77    Fog color blend enable/disable state is checked by calling glIsEnable
78    function with GL_FOG_BLEND_COLOR_SGIX parameter.
79
80    When PushAttrib is called with FOG_BIT enabled, the state of the
81    fog color and alpha blend is pushed. When an attribute set
82    that includes enable information is popped, the state of the fog
83    color and alpha blend is restored to the pushed value.
84
85Additions to the GLX Specification
86
87    None
88
89Errors
90
91    None
92
93New State
94
95    Get Value                   Get Command             Type            Initial Value   Attribute
96    ---------                   -----------             ----            -------------   ---------
97    FOG_BLEND_ALPHA_SGIX             IsEnabled           B                 FALSE           fog
98    FOG_BLEND_COLOR_SGIX             IsEnabled           B                 TRUE            fog
99
100
101New Implementation Dependent State
102
103    None
104
105