Comment # 18
on bug 93594
from Kai
(In reply to Marek Olšák from comment #10) > (In reply to Michel Dänzer from comment #9) > > Note that AFAIK using things like derivatives in non-uniform control flow > > isn't supported by GLSL. What's the original GLSL shader? > > True. > > The GLSL shader is using discard followed by fwidth. This is undefined > behavior. > > Therefore, it's an application bug. > > The easy workaround would be to disable register allocation in st/mesa to > get a quasi-SSA form and trivially move KILL_IF to the end of the shader if > the app is detected to be Talos Principle. I forwarded this information to Croteam and Dean Sekulic answered: > Oh, just found out that discard instruction is treated as dynamic flow control > for some reason... :/ > > Will fix this! > > > On 19-02-16 8:21, Dean Sekulic wrote: >> I can't find any reference anywhere that doing fwidth() (or ddx/ddy for >> that matter) after discard should be undefined behavior... :/ >> >> GPUs should handle that case completely fine. >> >> Can you elaborate, please? Looks like there might be an update for The Talos Principle which will address this.
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