<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW --- - [Steam] Implement GLSL 1.30 (for older chipsets than SandyBridge)" href="https://bugs.freedesktop.org/show_bug.cgi?id=59187#c8">Comment # 8</a> on <a class="bz_bug_link bz_status_NEW " title="NEW --- - [Steam] Implement GLSL 1.30 (for older chipsets than SandyBridge)" href="https://bugs.freedesktop.org/show_bug.cgi?id=59187">bug 59187</a> from <a class="email" href="mailto:stereotype441@gmail.com" title="Paul Berry <stereotype441@gmail.com>"> Paul Berry</a> <pre>(In reply to <a href="show_bug.cgi?id=59187#c6">comment #6</a>) > This isn't only an IronLake-issue. > > This issue is related to any chipsets older then SandyBridge. Just a side note to anyone who decides to work on this bug; If you would like to try to make chipsets prior to Gen5 work, please have a look at section 6.2.3 ("Negative-W Clipping Errata") of the i965/G35 manual (pp133-138), available from <a href="https://01.org/linuxgraphics/documentation/intel%C2%AE-965-express-chipset-family-and-intel%C2%AE-g35-express-chipset-graphics-controller">https://01.org/linuxgraphics/documentation/intel%C2%AE-965-express-chipset-family-and-intel%C2%AE-g35-express-chipset-graphics-controller</a> Briefly, certain Gen4 chipsets contain a bug which causes vertices with a negative gl_Position.w value to be clipped incorrectly. The workaround uses some of the hardware that was intended to implement gl_ClipDistance[7] (specifically, bit "UC7", which is output by the vertex shader to help the fixed-function clipping hardware determine whether a vertex may be trivially accepted or rejected). At present, applying the workaround is easy, since we don't support gl_ClipDistance on those chipsets, so bit UC7 is otherwise unused. If we want to make Gen4 chipsets implement gl_ClipDistance properly, we'll need to carefully consider the interactions between the bug workaround and gl_ClipDistance[7]. You can find the workaround code in Mesa by searching for the text "has_negative_rhw_bug".</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the assignee for the bug.</li> </ul> </body> </html>