Now the bounding box for the light cache's voxel grid is calculated in
global space, rather than camera space as it was previously. This fixes
flickering lighting on static volumes with camera motion, caused by
the camera space bounding box changing from frame to frame.
After code review and experimentation, this commit makes some changes to the way that volumes are shaded. Previously, there were problems with the 'scattering' component, in that it wasn't physically correct - it didn't conserve energy and was just acting as a brightness multiplier. This has been changed to be more correct, so that as the light is scattered out of the volume, there is less remaining to penetrate through.
Since this behaviour is very similar to absorption but more useful, absorption has been removed and has been replaced by a 'transmission colour' - controlling the colour of light penetrating through the volume after it has been scattered/absorbed. As well as this, there's now 'reflection', a non-physically correct RGB multiplier for out-scattered light. This is handy for tweaking the overall colour of the volume, without having to worry about wavelength dependent absorption, and its effects on transmitted light. Now at least, even though there is the ability to tweak things non-physically, volume shading is physically based by default, and has a better combination of correctness and ease of use.
There's more detailed information and example images here:
http://wiki.blender.org/index.php/User:Broken/VolumeRendering
Also did some tweaks/optimisation:
* Removed shading step size (was a bit annoying, if it comes back, it will be in a different form)
* Removed phase function options, now just one asymmetry slider controls the range between back-scattering, isotropic scattering, and forward scattering. (note, more extreme values gives artifacts with light cache, will fix...)
* Disabled the extra 'bounce lights' from the preview render for volumes, speeds updates significantly
* Enabled voxeldata texture in preview render
* Fixed volume shadows (they were too dark, fixed by avoiding using the shadfac/AddAlphaLight stuff)
More revisions to come later...
* Fix for plane material preview render. Now, light cache aborts if there isn't enough volume, and falls back on non-cached single scattering. It still doesn't make much sense to render a plane as a volume, but for now in the preview it will shade the region in between the plane and the checker background.
Also, made the Outliner's horizontal scrollbar work better for keymaps view. It's still using an approximation of the width, but at least you can scroll now.
This is mostly a contribution from Raul 'farsthary' Hernandez - an approximation for
multiple scattering within volumes. Thanks, Raul! Where single scattering considers
the path from the light to a point in the volume, and to the eye, multiple scattering
approximates the interactions of light as it bounces around randomly within the
volume, before eventually reaching the eye.
It works as a diffusion process that effectively blurs the lighting information
that's already stored within the light cache.
A cloudy sky setup, with single scattering, and multiple scattering:
http://mke3.net/blender/devel/rendering/volumetrics/vol_sky_ss_ms.jpghttp://mke3.net/blender/devel/rendering/volumetrics/sky_ms.blend
To enable it, there is a menu in the volume panel (which needs a bit of cleanup, for
later), that lets you choose between self-shading methods:
* None: No attenuation of the light source by the volume - light passes straight
through at full strength
* Single Scattering: (same as previously, with 'self-shading' enabled)
* Multiple Scattering: Uses multiple scattering only for shading information
* Single + Multiple: Adds the multiple scattering lighting on top of the existing
single scattered light - this can be useful to tweak the strength of the effect,
while still retaining details in the lighting.
An example of how the different scattering methods affect the visual result:
http://mke3.net/blender/devel/rendering/volumetrics/ss_ms_comparison.jpghttp://mke3.net/blender/devel/rendering/volumetrics/ss_ms_comparison.blend
The multiple scattering methods introduce 3 new controls when enabled:
* Blur: A factor blending between fully diffuse/blurred lighting, and sharper
* Spread: The range that the diffuse blurred lighting spreads over - similar to a
blur width. The higher the spread, the slower the processing time.
* Intensity: A multiplier for the multiple scattering light brightness
Here's the effect of multiple scattering on a tight beam (similar to a laser). The
effect of the 'spread' value is pretty clear here:
http://mke3.net/blender/devel/rendering/volumetrics/ms_spread_laser.jpg
Unlike the rest of the system so far, this part of the volume rendering engine isn't
physically based, and currently it's not unusual to get non-physical results (i.e.
much more light being scattered out then goes in via lamps or emit). To counter this,
you can use the intensity slider to tweak the brightness - on the todo, perhaps there is a more automatic method we can work on for this later on. I'd also like to check
on speeding this up further with threading too.
This commit introduces a new texture ('Voxel Data'), used to load up saved voxel
data sets for rendering, contributed by Raúl 'farsthary' Fernández Hernández
with some additional tweaks. Thanks, Raúl!
The texture works similar to the existing point density texture, currently it
only provides intensity information, which can then be mapped (for example) to
density in a volume material. This is an early version, intended to read the
voxel format saved by Raúl's command line simulators, in future revisions
there's potential for making a more full-featured 'Blender voxel file format',
and also for supporting other formats too.
Note: Due to some subtleties in Raúl's existing released simulators, in order
to load them correctly the voxel data texture, you'll need to raise the
'resolution' value by 2. So if you baked out the simulation at resolution 50,
enter 52 for the resolution in the texture panel. This can possibly be fixed in
the simulator later on.
Right now, the way the texture is mapped is just in the space 0,0,0 <-> 1,1,1
and it can appear rotated 90 degrees incorrectly. This will be tackled, for now,
probably the easiest way to map it is with and empty, using Map Input -> Object.
Smoke test: http://www.vimeo.com/2449270
One more note, trilinear interpolation seems a bit slow at the moment, we'll
look into this.
For curiosity, while testing/debugging this, I made a script that exports a mesh
to voxel data. Here's a test of grogan (www.kajimba.com) converted to voxels,
rendered as a volume: http://www.vimeo.com/2512028
The script is available here: http://mke3.net/projects/bpython/export_object_voxeldata.py
* Another smaller thing, brought back early ray termination (was disabled
previously for debugging) and made it user configurable. It now appears as a new
value in the volume material: 'Depth Cutoff'. For some background info on what
this does, check:
http://farsthary.wordpress.com/2008/12/11/cutting-down-render-times/
* Also some disabled work-in-progess code for light cache
