| |
| Name |
| |
| SGIX_fog_factor_to_alpha |
| |
| Name Strings |
| |
| GL_SGIX_fog_factor_to_alpha |
| |
| Version |
| |
| $Date: 1999/02/19 17:04:27 $ $Revision: 1.4 $ |
| |
| Number |
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| XXX |
| |
| Dependencies |
| |
| OpenGL 1.2 is required |
| |
| Overview |
| |
| This extension defines a mechanism that allows to replace the |
| alpha component by the fog blending factor after the input |
| fragment has been blent with the fog color. This feature is |
| particularly useful for multipass fog when we want to use the |
| the framebuffer blend function in conjunction with the fog blend |
| function. |
| |
| New Procedures and Functions |
| |
| None |
| |
| Issues |
| |
| - Is that ok as a stand alone extension? Should we include it |
| somewhere else? |
| |
| - Should we make additions to the chapter 4, section 4.1.3 Alpha |
| test and 4.1.6 Blending? |
| |
| - Does this spec need to reference the earlier fog_blend.spec |
| that allows for the fragment alpha component to be blended |
| with the fog color? |
| |
| |
| New Tokens |
| |
| Accepted by the <cap> parameter of Enable, Disable, and IsEnabled |
| |
| GL_FOG_FACTOR_TO_ALPHA_SGIX 0xXXXX |
| |
| |
| Additions to Chapter 2 of the 1.2 Specification (OpenGL Operation) |
| |
| None |
| |
| Additions to Chapter 3 of the 1.2 Specification (Rasterization) |
| |
| 3.10 Fog |
| |
| ... (The rasterized fragment's A value is not changed by fog blending.)... |
| is removed and replaced by. |
| |
| The rasterized fragment alpha value is not changed by fog blending, |
| unless specified otherwise by enabling it with the GL_FACTOR_TO_ALPHA_SGIX |
| parameter in which case the A value is replaced by the fog |
| blending factor. This substitution occurs after the alpha test is |
| performed. If fog is disabled but fog-factor-to-alpha is enabled, the |
| fragment alpha coming out of the fog-factor-to-alpha in undefined. |
| |
| Additions to Chapter 4 of the 1.2 Specification (Per-Fragment Operations |
| and the Framebuffer) |
| |
| None |
| |
| Additions to Chapter 5 of the 1.2 Specification (Special Functions) |
| |
| None |
| |
| Additions to Chapter 6 of the 1.2 Specification (State and State Requests) |
| |
| None |
| |
| Additions to the GLX Specification |
| |
| None |
| |
| Errors |
| |
| None |
| |
| New State |
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| None |
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| New Implementation Dependent State |
| |
| Get Value Get Command Type Initial Value Attribute |
| --------- ----------- ---- ------------- --------- |
| FOG_FACTOR_TO_ALPHA_SGIX IsEnabled B FALSE fog |