Dropping the inlining hint for `light_tree_pdf` and reverting to the
default inlining thresholds for DPC++ compiler gives a ~4% speedup on
classroom and other scenes on Arc B580.
Pull Request: https://projects.blender.org/blender/blender/pulls/135042
This is an intermediate steps towards making lights actual geometry.
Light is now a subclass of Geometry, which simplifies some code.
The geometry is not added to the BVH yet, which would be the next
step and improve light intersection performance with many lights.
This makes object attributes work on lights.
Co-authored-by: Lukas Stockner <lukas@lukasstockner.de>
Pull Request: https://projects.blender.org/blender/blender/pulls/134846
In a previous commit (1), adjustments to light tree traversal were made
to try and skip distant lights when deciding which light to sample
while within a world volume.
The skip wasn't implemented properly, and as a result distant lights
were still included in the light tree traversal in that sitaution.
And due to the way the skip was implemented, there were some
unintialized variables used in the processing of the distant lights
importance which caused artifacts on some platforms.
This commit fixes this issue by reverting the skip of distant lights
in that situation.
(1) blender/blender@6fbc958e89
Pull Request: https://projects.blender.org/blender/blender/pulls/132344
Check was misc-const-correctness, combined with readability-isolate-declaration
as suggested by the docs.
Temporarily clang-format "QualifierAlignment: Left" was used to get consistency
with the prevailing order of keywords.
Pull Request: https://projects.blender.org/blender/blender/pulls/132361
* Use .empty() and .data()
* Use nullptr instead of 0
* No else after return
* Simple class member initialization
* Add override for virtual methods
* Include C++ instead of C headers
* Remove some unused includes
* Use default constructors
* Always use braces
* Consistent names in definition and declaration
* Change typedef to using
Pull Request: https://projects.blender.org/blender/blender/pulls/132361
When a scene contains distant lights and local lights, the first step
of the light tree traversal is to compute the importance of
distant lights vs local lights and pick one based on a random number.
In the specific case of when there is only one distant light,
the line of code that had been changed in this commit
effectively reduced to:
`min_importance = fast_cosf(x) < cosf(x) ? 0.0 : compute_min_importance`
And depending on the hardware, compiler, and the specific value being
tested, different configurations could take different code paths.
This commit fixes this issue by turning the comparison into
`fast_cosf(x) < fast_cosf(x)`.
---
Why does `cos_theta_plus_theta_u < cosf(bcone.theta_e - bcone.theta_o)`
reduce to `fast_cos(x) < cos(x)` in this specific case?
- `cos_theta_plus_theta_u` is computed as
`cos_theta * cos_theta_u - sin_theta * sin_theta_u`
- `cos_theta` is always 1.0 in the case of a single distant light.
- `cos_theta_u` is computed earlier as `fast_cosf(theta_e)` in
`distant_light_tree_parameters()`
- `sin_theta` is zero, and so that side of the equation doesn't matter.
This reduces `cos_theta_plus_theta_u` to `fast_cosf(theta_e)`.
`cosf(bcone.theta_e - bcone.theta_o)` reduces to `cosf(bcone.theta_e)`
because for the case of a single distant light `theta_o` is always 0.
Pull Request: https://projects.blender.org/blender/blender/pulls/131932
In volume segment, the minimal angle formed by the emitter bounding cone
axis and the vector pointing from the cluster centroid to any point on
the ray is computed via `dot(bcone.axis, point_to_centroid)`, see Fig.8.
in paper.
For distant light this angle is 0, but due to numerical issues this is
not always true. Therefore explicitly assign `-bcone.axis` to
`point_to_centroid` in this case.
Pull Request: https://projects.blender.org/blender/blender/pulls/129489
Gitea would complain the apostrophe in one of the code comments in
tree.h was an ambiguous Unicode character. So fix it by swapping it
for a more common apostrophe type.
Use a bounding sphere instead of the corners of a bounding box to
compute the subtended angle of a light tree node.
Using the corners of the bounding box was an underestimate in some
scenes, causing some light tree nodes being incorrectly skipped.
Using the subtended angle of a bounding sphere is an overestimate, but
it covers the entire node and would not skip any valid contribution,
and no other reliable algorithm to compute the minimal enclosing angle
is known to us.
We expect some increase in noise due to overestimation, but this has
not been observed yet, in our benchmark scenes only a difference in
noise is visible.
Thanks to Weizhen for the suggestion to use the bounding sphere.
Pull Request: https://projects.blender.org/blender/blender/pulls/126625
The original paper only considers the minimal distance of the cluster to
the ray, not the interval length, resulting in low weight for distant
lights that have large influence over a long distance.
This commit modifies the measure by considering `theta_b - theta_a` for
local lights and the ray length `t` for distant lights.
Pull Request: https://projects.blender.org/blender/blender/pulls/123537
This fixes#69535 and #98930.
We use a equi-solid-angle sampling algorithm for rectangular area lights,
but it is not particularly robust for small area lights (either small
in general and/or small because it's being viewed from grazing angles).
The actual sampling part is fine since it just gets clamped into the
valid area anyways, and the difference isn't notable for small lights.
However, we also need to compute the solid angle to get the sampling PDF,
and that computation is quite sensitive to numerical issues for small
values.
Therefore, this commit adds a fallback path for small values, which instead
uses the classic equi-area sampling PDF term times the area-to-solid-angle
Jacobian term. This approximation assumes that all points on the light have
the same distance and angle to the sampling point, which is of course not
strictly the case, but it's close enough for small area lights and better
than failing altogether.
Pull Request: https://projects.blender.org/blender/blender/pulls/122323
Reformulates some terms in the equi-solid-angle rectangle sampling code to
handle small area lamps better, and allows for some rounding error in the
check whether the sampled position is inside the area light.
Pull Request: https://projects.blender.org/blender/blender/pulls/122323
In the original paper, the falloff inside `bcone.theta_e` is assumed to
be `pi/2`, which is too large for spot light and resulted in an
overestimation near the cone boundary.
To address this issue, attenuate the energy of a spot light using the
minimal possible angle formed by the light axis and the shading point
when traversing the light tree.
Ref: #122362
Pull Request: https://projects.blender.org/blender/blender/pulls/122667
The refactor in 97d9bbbc97 changed the way q is computed in the spherical triangle sampling code. While the new approach is more efficient and saves a few operations, it introduces numerical precision issues for skinny/small (spherical) triangles.
Therefore, this change moves the computation of q back to the method from the paper, while keeping the more efficient solid angle computation.
Pull Request: https://projects.blender.org/blender/blender/pulls/119224
it is difficult to keep in mind when MIS weight is needed, better to
handle this logic in the lower-level functions.
This reduces code duplication in many places.
it is not clear from which point the `cos_theta_u` should be computed in
volume segment, so the original implementation was mixing the closest point
and the point where the minimal angle is formed.
Use the closest point on segment as a conservative measure.
Pull Request: https://projects.blender.org/blender/blender/pulls/119965
in the test scene `all_light_types_in_volume.blend`, `theta - theta_o -
theta_u` is slightly above the threshold. Even if we do a strict check
with `acos` on the failing cases, it will go to the other branch and
deliver a result which is also 1.0f. Better to relax the threshold.
The same random number was used when sampling from the volume segment
and from the direct scattering position, causing correlation issues with
light tree.
To solve this problem, we ensure the same light is picked for
volume segment/direct scattering, equiangular/distance sampling by
sampling the light tree only once in volume segment. From the direct
scattering position in volume, we sample a position on the picked light
as usual. If sampling from the light tree fails, we continue with
indirect scattering.
For unbiased MIS weight for forward sampling, we retrieve the `P`, `D`
and `t` used in volume segment for traversing the light tree.
The main changes are:
1. `light_tree_sample()` and `light_distribution_sample()` now only pick
lights. Sampling a position on light is done separately via
`light_sample()`.
2. `light_tree_sample()` is now only called only once from volume
segment. For direct lighting we call `light_sample()`.
3. `light_tree_pdf()` now has a template `<in_volume_segment>`.
4. A new field `emitter_id` is added to struct `LightSample`, which just
stores the picked emitter index.
5. Additional field `previous_dt = ray->tmax - ray->tmin` is added to
`state->ray`, because we need this quantity for computing the pdf.
6. Distant/Background lights are also picked by light tree in volume
segment now, because we have no way to pick them afterwards. The direct
sample event for these lights will be handled by
`VOLUME_SAMPLE_DISTANCE`.
7. Original paper suggests to use the maximal importance, this results
in very poor sampling probability for distant and point lights therefore
excessive noise. We have a minimal importance for surface to balance, we
could do the same for volume but I do not want to spend much time on
this now. Just doing `min_importance = 0.0f` seems to do the job
okayish. This way we still won't sample the light with zero
`max_importance`.
The current solution might perform worse with distance sampling, because
the light tree measure is biased towards equiangular sampling. However,
it is difficult to perform MIS between equiangular and distance sampling
if different lights are picked for each method. This is something we can
look into in the future if proved to be a serious regression.
Pull Request: https://projects.blender.org/blender/blender/pulls/119389
When using light linking with the light tree, the root index of a
mesh light subtree can be 0. The current code assumed this wasn't
possible, and as such it caused rendering issues, specifically the
incorrect computation of the PDF of certain mesh lights during
forward path tracing.
So we adjust the code to allow mesh light subtree root node
indices of 0.
This was worked on by Alaska, Sergey, and Weizhen
Pull Request: https://projects.blender.org/blender/blender/pulls/119770
By restricting the sample range along the ray to the valid segment.
Supports
**Mesh Light**
- [x] restrict the ray segment to the side with MIS
**Area Light**
- [x] when the spread is zero, find the intersection of the ray and the bounding box/cylinder of the rectangle/ellipse area light beam
- [x] when the spread is non-zero, find the intersection of the ray and the minimal enclosing cone of the area light beam
*note the result is also unbiased when we just consider the cone from the sampled point in volume segment. Far away from the light source it's less noisy than the current solution, but near the light source it's much noisier. We have to restrict the sample region on the area light to the part that lits the ray then, I haven't tried yet to see if it would be less noisy.*
**Point Light**
- [x] the complete ray segment should be valid.
**Spot Light**
- [x] intersect the ray with the spot light cone
- [x] support non-zero radius
Pull Request: https://projects.blender.org/blender/blender/pulls/119438
For spherical spot light, when the shading point is close to the light
source, we switch to sampling the light spread instead of the visible
cone from the shading point. This has the benefit of less noise when the
spread is small.
However, the light spread sampling was not considering non-uniform
object scaling, where the actual spread might be different.
This patch switches sampling method only when the smallest enclosing
spread cone is smaller than the visible cone from the shading point.
An alternative method would be to compute the actual solid angle of the
scaled cone, and sample from the scaled cone. However, that involves
ray transformation and modifying the sampling pdf and angle. Since
non-uniform scaling is rather a niche case, it's probably not worth the
computation effort.
Pull Request: https://projects.blender.org/blender/blender/pulls/119661
Ref: #118534
turns out `in_volume_segment` does need to be checked. If the ray origin
lies on the wrong side of the mesh light, part of the ray could still be
lit by the other side, so the sample should not be considered invalid.
Pull Request: https://projects.blender.org/blender/blender/pulls/119529
if emission sampling is not set, we do not use MIS weight when sampling
from the BSDF, but we were still drawing samples from the light,
resulting in double contribution.
Pull Request: https://projects.blender.org/blender/blender/pulls/118534
Add new "Soft Falloff" option on point and spot light that uses
the old light behavior from Blender versions before 4.0. Blend
files saved with those older versions will use the option.
This option is enabled by default on new lights.
Fix#114241
Co-authored-by: Weizhen Huang <weizhen@blender.org>
Co-authored-by: Clément Foucault <foucault.clem@gmail.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/117832
Along with the 4.1 libraries upgrade, we are bumping the clang-format
version from 8-12 to 17. This affects quite a few files.
If not already the case, you may consider pointing your IDE to the
clang-format binary bundled with the Blender precompiled libraries.
The solid angle computation for the sampling/PDF code was running into
cancellation issues for small solid angles.
Reformulating the terms using asin() instead avoids this.
based on concentric disk mapping.
Concentric disk mapping was already present, but not used everywhere.
Now `sample_cos_hemisphere()`, `sample_uniform_hemisphere()`, and
`sample_uniform_cone()` use concentric disk mapping.
This changes the noise in many test images.
Pull Request: https://projects.blender.org/blender/blender/pulls/109774
