llvmpipe takes a number of shortcuts in the interest of speed which cause inaccurate texturing. Try running with
GALLIVM_DEBUG=no_rho_approx,no_brilinear,no_quad_lod and see if the issue still occurs. Cheers, -ilia On Thu, Apr 11, 2019 at 8:30 AM Dominik Drees <dominik.dr...@wwu.de> wrote: > > Hello, everyone! > > I have a question regarding the interpolation precision of llvmpipe. > Feel free to redirect me to somewhere else if this is not the right > place to ask. Consider the following scenario: In a fragment shader we > are sampling from a 16x16, 8 bit texture with values between 0 and 3 > using linear interpolation. Then we write white to the screen if the > sampled value is > 1/255 and black otherwise. The output looks very > different when rendered with llvmpipe compared to the result produced by > rendering hardware (for both intel (mesa i965) and nvidia (proprietary > driver)). > > I've uploaded examplary output images here (https://imgur.com/a/D1udpez) > and the corresponding fragment shader here (https://pastebin.com/pa808Req). > > My hypothesis is that llvmpipe (in contrast to hardware) only uses 8 bit > for the interpolation computation when reading from 8 bit textures and > thus loses precision in the lower bits. Is that correct? If so, does > anyone know of a workaround? > > A little bit of background about the use case: We are trying to move the > CI of Voreen (https://www.uni-muenster.de/Voreen/) to the Gitlab-CI > running in docker without any hardware dependencies. Using llvmpipe for > our regression tests works in principle, but shows significant > differences in the raycasting rendering of an 8-bit-per-voxel dataset. > (The effect is of course less visible than the constructed example case > linked above, but still quite noticeable for a human.) > > Any help or pointers would be appreciated! > > Best, > Dominik > > -- > Dominik Drees > > Department of Computer Science > Westfaelische Wilhelms-Universitaet Muenster > > email: dominik.dr...@wwu.de > web: https://www.wwu.de/PRIA/personen/drees.shtml > phone: +49 251 83 - 38448 > > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
