Basically the title says it all, volume stack initialization now is aware that
camera might be inside of the volume. This gives quite noticeable render time
regressions in cases camera is in the volume (didn't measure them yet) because
this requires quite a few of ray-casting per camera ray in order to check which
objects we're inside. Not quite sure if this might be optimized.
But the good thing is that we can do quite a good job on detecting whether
camera is outside of any of the volumes and in this case there should be no
time penalty at all (apart from some extra checks during the sync state).
For now we're only doing rather simple AABB checks between the viewplane and
volume objects. This could give some false-positives, but this should be good
starting point.
Need to mention panoramic cameras here, for them it's only check for whether
there are volumes in the scene, which would lead to speed regressions even if
the camera is outside of the volumes. Would need to figure out proper check
for such cameras.
There are still quite a few of TODOs in the code, but the patch is good enough
to start playing around with it checking whether there are some obvious mistakes
somewhere.
Currently the feature is only available in the Experimental feature sey, need
to solve some of the TODOs and look into making things faster before considering
the feature is ready for the official feature set. This would still likely
happen in current release cycle.
Reviewers: brecht, juicyfruit, dingto
Differential Revision: https://developer.blender.org/D794
Transparent objects could become subtly visible by the different sampling
patterns for pixels covered and not covered by the object. It still converged
to the right solution but that can take a while. Now we try to use the same
sampling pattern here.
This is done by adding a Volume Scatter node. In many cases you will want to
add together a Volume Absorption and Volume Scatter node with the same color
and density to get the expected results.
This should work with branched path tracing, mixing closures, overlapping
volumes, etc. However there's still various optimizations needed for sampling.
The main missing thing from the volume branch is the equiangular sampling for
homogeneous volumes.
The heterogeneous scattering code was arranged such that we can use a single
stratified random number for distance sampling, which gives less noise than
pseudo random numbers for each step. For volumes where the color is textured
there still seems to be something off, needs to be investigated.
Volumes can now have textured colors and density. There is a Volume Sampling
panel in the Render properties with these settings:
* Step size: distance between volume shader samples when rendering the volume.
Lower values give more accurate and detailed results but also increased render
time.
* Max steps: maximum number of steps through the volume before giving up, to
protect from extremely long render times with big objects or small step sizes.
This is much more compute intensive than homogeneous volume, so when you are not
using a texture you should enable the Homogeneous Volume option in the material
or world for faster rendering.
One important missing feature is that Generated texture coordinates are not yet
working in volumes, and they are the default coordinates for nearly all texture
nodes. So until that works you need to plug in object texture coordinates or a
world space position.
This is work by "storm", Stuart Broadfoot, Thomas Dinges and myself.
This works pretty much as you would expect, overlapping volume objects gives
a more dense volume. What did change is that world volume shaders are now
active everywhere, they are no longer excluded inside objects.
This may not be desirable and we need to think of better control over this.
In some cases you clearly want it to happen, for example if you are rendering
a fire in a foggy environment. In other cases like the inside of a house you
may not want any fog, but it doesn't seem possible in general for the renderer
to automatically determine what is inside or outside of the house.
This is implemented using a simple fixed size array of shader/object ID pairs,
limited to max 15 overlapping objects. The closures from all shaders are put
into a single closure array, exactly the same as if an add shader was used to
combine them.
This is the simplest possible volume rendering case, constant density inside
the volume and no scattering or emission. My plan is to tweak, verify and commit
more volume rendering effects one by one, doing it all at once makes it
difficult to verify correctness and track down bugs.
Documentation is here:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Materials/Volume
Currently this hooks into path tracing in 3 ways, which should get us pretty
far until we add more advanced light sampling. These 3 hooks are repeated in
the path tracing, branched path tracing and transparent shadow code:
* Determine active volume shader at start of the path
* Change active volume shader on transmission through a surface
* Light attenuation over line segments between camera, surfaces and background
This is work by "storm", Stuart Broadfoot, Thomas Dinges and myself.
This to avoids build conflicts with libc++ on FreeBSD, these __ prefixed values
are reserved for compilers. I apologize to anyone who has patches or branches
and has to go through the pain of merging this change, it may be easiest to do
these same replacements in your code and then apply/merge the patch.
Ref T37477.
