1 2Name 3 4 SGIX_fog_factor_to_alpha 5 6Name Strings 7 8 GL_SGIX_fog_factor_to_alpha 9 10Version 11 12 $Date: 1999/02/19 17:04:27 $ $Revision: 1.4 $ 13 14Number 15 16 XXX 17 18Dependencies 19 20 OpenGL 1.2 is required 21 22Overview 23 24 This extension defines a mechanism that allows to replace the 25 alpha component by the fog blending factor after the input 26 fragment has been blent with the fog color. This feature is 27 particularly useful for multipass fog when we want to use the 28 the framebuffer blend function in conjunction with the fog blend 29 function. 30 31New Procedures and Functions 32 33 None 34 35Issues 36 37 - Is that ok as a stand alone extension? Should we include it 38 somewhere else? 39 40 - Should we make additions to the chapter 4, section 4.1.3 Alpha 41 test and 4.1.6 Blending? 42 43 - Does this spec need to reference the earlier fog_blend.spec 44 that allows for the fragment alpha component to be blended 45 with the fog color? 46 47 48New Tokens 49 50 Accepted by the <cap> parameter of Enable, Disable, and IsEnabled 51 52 GL_FOG_FACTOR_TO_ALPHA_SGIX 0xXXXX 53 54 55Additions to Chapter 2 of the 1.2 Specification (OpenGL Operation) 56 57 None 58 59Additions to Chapter 3 of the 1.2 Specification (Rasterization) 60 61 3.10 Fog 62 63 ... (The rasterized fragment's A value is not changed by fog blending.)... 64 is removed and replaced by. 65 66 The rasterized fragment alpha value is not changed by fog blending, 67 unless specified otherwise by enabling it with the GL_FACTOR_TO_ALPHA_SGIX 68 parameter in which case the A value is replaced by the fog 69 blending factor. This substitution occurs after the alpha test is 70 performed. If fog is disabled but fog-factor-to-alpha is enabled, the 71 fragment alpha coming out of the fog-factor-to-alpha in undefined. 72 73Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations 74and the Framebuffer) 75 76 None 77 78Additions to Chapter 5 of the 1.2 Specification (Special Functions) 79 80 None 81 82Additions to Chapter 6 of the 1.2 Specification (State and State Requests) 83 84 None 85 86Additions to the GLX Specification 87 88 None 89 90Errors 91 92 None 93 94New State 95 96 None 97 98New Implementation Dependent State 99 100 Get Value Get Command Type Initial Value Attribute 101 --------- ----------- ---- ------------- --------- 102 FOG_FACTOR_TO_ALPHA_SGIX IsEnabled B FALSE fog 103