This commit introduces a SSS-oriented intersection structure which is replacing
old logic of having separate arrays for just intersections and shader data and
encapsulates all the data needed for SSS evaluation.
This giver a huge stack memory saving on GPU. In own experiments it gave 25%
memory usage reduction on GTX560Ti (722MB vs. 946MB).
Unfortunately, this gave some performance loss of 20% which only happens on GPU.
This is perhaps due to different memory access pattern. Will be solved in the
future, hopefully.
Famous saying: won in memory - lost in time (which is also valid in other way
around).
It was possible to miss some intersection caused by wrong barycentric
coordinates sign.
Cases when one of the coordinate is zero and other are negative was not
handled correct.
Issue was caused by wrong intersection distance scaling on instance pop,
which could cause intersection distance to become zero, confusing following
intersection checks.
Epsilon was quite arbitrary for GPU, replaced with checking for zero-sized faces.
It should solve both original report and the new one. After the release we can check
why GPU doesn't produce accurate math here and go to the root of the issue.
Found a way to make AVX2 CPUs happy by reshuffling instructions a bit,
so now there's no weird precision errors happening in there.
This solves some render speed regressions on CPU, but unfortunately
this doesn't help for GPU rendering.
Initial idea was to optimize calculation a bit by skipping calculation of actual
triangle edges and use vector from ray origin to triangles. In practice this
optimization didn't quite work in cases when origin point is too close to the
triangle.
Let's do 2.76 with a bit more complicated calculation, still looking into exact
reasons why watertight intersections fails in certain cases, but actual fix might
bit be ready so soon.
This fixes wrong eyes on the lady from T46013.
The issue was caused by some numeric instability in triangle intersection which
was visible on avx2 CPUs and GPUs (at least sm_20 here) but maybe some others
too.
Committing rather a workaround for now to be safe for the release, still need
some investigation.
From tests with grass field from Gooseberry project didn't see measurable
slowdown.
This gives quite the same problems as experimental CUDA kernels
and for until it's found a root cause of the problem we'd just
explicitly uninline the function.
TODO: We might want to refactor debug passes into PASS_DEBUG and some
debug_type (similar to Blender's side passes) to avoid issue of running
out of bits.
This commit contains all the work related on the AMD megakernel split work
which was mainly done by Varun Sundar, George Kyriazis and Lenny Wang, plus
some help from Sergey Sharybin, Martijn Berger, Thomas Dinges and likely
someone else which we're forgetting to mention.
Currently only AMD cards are enabled for the new split kernel, but it is
possible to force split opencl kernel to be used by setting the following
environment variable: CYCLES_OPENCL_SPLIT_KERNEL_TEST=1.
Not all the features are supported yet, and that being said no motion blur,
camera blur, SSS and volumetrics for now. Also transparent shadows are
disabled on AMD device because of some compiler bug.
This kernel is also only implements regular path tracing and supporting
branched one will take a bit. Branched path tracing is exposed to the
interface still, which is a bit misleading and will be hidden there soon.
More feature will be enabled once they're ported to the split kernel and
tested.
Neither regular CPU nor CUDA has any difference, they're generating the
same exact code, which means no regressions/improvements there.
Based on the research paper:
https://research.nvidia.com/sites/default/files/publications/laine2013hpg_paper.pdf
Here's the documentation:
https://docs.google.com/document/d/1LuXW-CV-sVJkQaEGZlMJ86jZ8FmoPfecaMdR-oiWbUY/edit
Design discussion of the patch:
https://developer.blender.org/T44197
Differential Revision: https://developer.blender.org/D1200
This replaces sequential ray moving followed with scene intersection with
single BVH traversal, which gives us all possible intersections.
Only implemented for CPU, due to qsort and a bigger memory usage on GPU
which we rather avoid. GPU still uses the regular bvh volume intersection code, while CPU now uses the new code.
This improves render performance for scenes with:
a) Camera inside volume mesh
b) SSS mesh intersecting a volume mesh/domain
In simple volume files (not much geometry) performance is roughly the same
(slightly faster). In files with a lot of geometry, the performance
increase is larger. bmps.blend with a volume shader and camera inside the
mesh, it renders ~10% faster here.
Patch by Sergey and myself.
Differential Revision: https://developer.blender.org/D1264
This more a workaround for CUDA optimizer which can't optimize clamp(x, 0, 1)
into a single instruction and uses 4 instructions instead.
Original patch by @lockal with own modification:
Don't make changes outside of the kernel. They don't make any difference
anyway and term saturate() has a bit different meaning outside of kernel.
This gives around 2% of speedup in Barcelona file, but in more complex shader
setups with lots of math nodes with clamping speedup could be much nicer.
Subscribers: dingto
Projects: #cycles
Differential Revision: https://developer.blender.org/D1224
This way we can get rid of inefficient memory usage caused by BVH boundbox
part being unused by leaf nodes but still being allocated for them. Doing
such split allows to save 6 of float4 values for QBVH per leaf node and 3
of float4 values for regular BVH per leaf node.
This translates into following memory save using 01.01.01.G rendered
without hair:
Device memory size Device memory peak Global memory peak
Before the patch: 4957 5051 7668
With the patch: 4467 4562 7332
The measurements are done against current master. Still need to run speed tests
and it's hard to predict if it's faster or not: on the one hand leaf nodes are
now much more coherent in cache, on the other hand they're not so much coherent
with regular nodes anymore.
Reviewers: brecht, juicyfruit
Subscribers: venomgfx, eyecandy
Differential Revision: https://developer.blender.org/D1236
Issue was caused by MSVC not being able to optimize some code out in the same
way as GCC/Clang does, so now that parts of code are explicitly unfolded in
order to help compilers out.
This makes speed loss much less drastic on my laptop. That's probably as good
as we can do with MSVC without investing infinite amount of time looking trying
to workaround the optimizer.
This argument was unused and got nicely optimized out. But once it
starts to be using registers are getting stressed really crazy,
causing slow down of render.
It's not that bad because this typo could only caused not really
efficient BVH traversal, causing higher render times. Not as if
it was causing render artifacts.
This inconsistency drove me totally crazy, it's really confusing
when it's inconsistent especially when you work on both Cycles and
Blender sides.
Shouldn;t cause merge PITA, it's whitespace changes only, Git should
be able to merge it nicely.
The fix was really flacky, in terms during speed benchmarks i had
abort() in the fallback block to be sure it never runs in production
scenes, but that affected on the optimization as well. Without this
abort there's quite bad slowdown of 5-7% on the renders even tho
the Pleucker fallback was never run.
This is all weird and for now reverting the change which affects on
all the production scenes and will look into alternative fixes for
the original issue with precision loss on huge planes.
This reverts commit 9489205c5c.
The issue was caused by numerical instability whrn having ray origin close to a huge
triangle, which could have aused bad ray distance check.
Watertight Woop intersection isn't really addressing such cases, it's dealing with
small triangles far away from the ray origin instead, so it's a bit tricky yo make
it working reliably.
While we're quite close to the release it's safer to do check in Pleaucker coordinates
if ray close to a huge triangle. Likely this additional check combined with some other
tweaks to the code doesn't cause measurable slowdown in the scenes tested here.
After the release we can play a bit more with this code in order to make it more
stable without Pleucker fallback.
From more investigation of the numeric failures in the kernel it appears
the check was rather correct. But in theory it;s also needed for the motion
triangles.
This is the same issue T43475: SSE4 code is more robust to non-finite values
in the ray origin/direction. So for now added a check before doing BVH traversal
for pre-SSE4 CPUs.
For sure actual root of the issue is a bit different and much more tricky to
solve, especially without disturbing render results too much. Still looking
into this.
In any case, it's kinda fine to have such a check, we might later make it to be
a kernel_assert() instead of just a return.
