From: <no...@so...> - 2001-01-21 21:31:35
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Bug #129606, was updated on 2001-Jan-21 13:31 Here is a current snapshot of the bug. Project: Direct Rendering Infrastructure Category: Core OpenGL Status: Open Resolution: None Bug Group: Rendering Error Priority: 5 Submitted by: joshagam Assigned to : nobody Summary: Possibly incorrect alpha in lighting Details: The OpenGL redbook and bluebook both indicate that the alpha of the various lighting components (ambient, specular, diffuse, etc.) are all summed together, but in DRI/Mesa/etc., it only uses the alpha component from the diffuse material parameter, and it also seems to just use that parameter (rather than calculating it as part of the lighting equations). That is, rather than treating the alpha component like the other color components, Mesa's lighting equations seem to just grab the diffuse parameter's alpha component and call it a day. I can't find any official documentation stating that the alpha component is to be treated the same as the red, green and blue compoents, but the documentation would indicate that it is, and there are a signifigant number of alpha effects (soap bubbles, etc.) which rely on the alpha component being treated this way which aren't easy to emulate through other means. As a simple example, to have a transparent but reflective soap bubble, you'd have diffuse at, say, 1,1,1,0.1 but specular at 1,1,1,1, so that the bubble itself is mostly transparent, but the hilight is opaque. Similarly, there are a lot of neat effects you can have by putting a non-1 alpha component into various lights. Is this an erroneous shortcut being taken in Mesa, or is the OpenGL documentation vague enough that either behavior is considered acceptable? Thanks in advance. For detailed info, follow this link: http://sourceforge.net/bugs/?func=detailbug&bug_id=129606&group_id=387 |