Trivial changes to vertex shader sometimes change vertex positions

Found a bug? Post information about it here so we can fix it!

Moderator: Moderators

Post Reply
plygon
Posts: 4
Joined: Fri Nov 23, 2018 7:40 pm

Trivial changes to vertex shader sometimes change vertex positions

Post by plygon » Sat Dec 15, 2018 2:49 am

Image

I'm not at all an expert in OpenGL, but I am confident that this is a bug. When I remove this useless variable from my fragment shader, the vertex positions change. (The smaller triangle is the correct one)

I'm sorry if this has been posted before, I did a quick search and didn't see it.

User avatar
Kjell
Posts: 1677
Joined: Sat Feb 23, 2008 11:15 pm

Re: Trivial changes to vertex shader sometimes change vertex positions

Post by Kjell » Sat Dec 15, 2018 12:51 pm

Hi plygon,

Are you sure you're not getting any GLSL compilation errors in the log panel? Some GPU drivers are a bit particular when it comes to defining variables that don't actually get used for anything.

K

plygon
Posts: 4
Joined: Fri Nov 23, 2018 7:40 pm

Re: Trivial changes to vertex shader sometimes change vertex positions

Post by plygon » Sat Dec 15, 2018 5:16 pm

I am not getting any GSL compilation errors (though that seems like the only explanation)

I do get an error that I think is unrelated, but it only happens when I switch to a different element while the preview is not running. I get "Access violation at address 569648C0 in module 'if75icd32.dll'.Read of address 00000024".

Two other things I noticed:
-The name of the variable does not matter.
-It will only render correctly if the variable has something to do with the "vertex" attribute. Setting it to "vertex.x - vertex.x" works, but setting it to "0.0" doesn't.

User avatar
VilleK
Site Admin
Posts: 1964
Joined: Mon Jan 15, 2007 4:50 pm
Location: Stockholm, Sweden
Contact:

Re: Trivial changes to vertex shader sometimes change vertex positions

Post by VilleK » Mon Dec 17, 2018 8:17 am

Hi,

I can't really explain that other than the GLSL-compilation is entirely handled in the graphics driver. So it might be a bug/quirk in your Intel GPU driver.

Post Reply