* Convert all code to use new functions.
* Branch maintainers may want to skip this commit, and run this
conversion script instead, if they use a lot of math functions
in new code:
http://www.pasteall.org/9052/python
Volumes can now receive shadows from external objects, either raytraced shadows or shadow maps.
To use external shadows, enable 'external shadows' in volume material 'lighting' panel. This an extra toggle since it causes a performance hit, but this can probably be revisited/optimised when the new raytrace accelerator is integrated. For shadow maps at least, it's still very quick.
Renamed 'scattering mode' to 'lighting mode' (a bit simpler to understand), and the options inside. Now there's:
- Shadeless
takes light contribution, but without shadowing or self-shading (fast)
good for fog-like volumes, such as mist, or underwater effects
- Shadowed (new)
takes light contribution with shadows, but no self-shading. (medium)
good for mist etc. with directional light sources
eg. http://vimeo.com/6901636
- Shaded
takes light contribution with internal/external shadows, and self shading (slower)
good for thicker/textured volumes like smoke
- Multiple scattering etc (still doesn't work properly, on the todo).
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Since this behaviour is very similar to absorption but more useful, absorption has been removed and has been replaced by a 'transmission colour' - controlling the colour of light penetrating through the volume after it has been scattered/absorbed.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.
Integration is still very rough around the edges and WIP, but it works, and can render smoke (using new Smoke format in Voxel Data texture) --> http://vimeo.com/6030983
More to come, but this makes things much easier to work on for me :)
* Added support for additional file types in the voxel data texture. I added
support for 8 bit raw files, but most notably for image sequences.
Image sequences generate the voxel grid by stacking layers of image slices on top
of each other to generate the voxels in the Z axis - the number of slices in the
sequence is the resolution of the voxel grid's Z axis.
i.e. http://mke3.net/blender/devel/rendering/volumetrics/skull_layers.jpg
The image sequence option is particularly useful for loading medical data into
Blender. 3d medical data such as MRIs or CT scans are often stored as DICOM
format image sequences. It's not in Blender's scope to support the DICOM format,
but there are plenty of utilities such as ImageMagick, Photoshop or OsiriX that
can easily convert DICOM files to formats that Blender supports, such as PNG or JPEG.
Here are some example renderings using these file formats to load medical data:
http://vimeo.com/5242961http://vimeo.com/5242989http://vimeo.com/5243228
Currently the 8 bit raw and image sequence formats only support the 'still'
rendering feature.
* Changed the default texture placement to be centred around 0.5,0.5,0.5, rather
than within the 0.0,1.0 cube. This is more consistent with image textures, and it
also means you can easily add a voxel data texture to a default cube without
having to mess around with mapping.
* Added some more extrapolation modes such as Repeat and Extend rather than just clipping
http://mke3.net/blender/devel/rendering/volumetrics/bradybunch.jpg
* Changed the voxel data storage to use MEM_Mapalloc (memory mapped disk cache)
rather than storing in ram, to help cut down memory usage.
* Refactored and cleaned up the code a lot. Now the access and interpolation code
is separated into a separate voxel library inside blenlib. This is now properly
shared between voxel data texture and light cache (previously there was some
duplicated code).
* Made volume light cache support non-cubic voxel grids. Now the resolution
specified in the material properties is used for the longest edge of the volume
object's bounding box, and the shorter edges are proportional (similar to how
resolution is calculated for fluid sim domains).
This is *much* more memory efficient for squashed volume regions like clouds
layer bounding boxes, allowing you to raise the resolution considerably while
still keeping memory usage acceptable.
This changes the effect of the multiple scattering approximation to be more
physically plausible (and easier to use) by making it conserve energy.
Previously, the multiple scattering could show wildly different results
based on the spread settings, often outputting much more light than was put
in (via lamps), which is physically incorrect and made it difficult to use
by requiring a lot of tweaking of the intensity value.
This fixes it to some extent with a simple normalization, where it scales
the light energy after multiple scattering to be the same as what was
previously there in the light cache via single scattering. This means that
using the default intensity of 1.0 should give good results by default,
although you can still use it to tweak the effect.
Note: This will render differently if you've already set up a .blend using
multiple scattering with the old code, so you'll need to tweak older files.
Setting the intensity back to the default 1.0 should be good though.
* Smaller thing - fixed the camera view vector stuff up a bit in light
cache, it now gives much more similar results to non-light cache when using
anisotropic scattering.
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.
* Multithreaded volume light cache
While the render process itself is multithreaded, the light cache pre-process
previously wasn't (painfully noticed this the other week rendering on some
borrowed octocore nodes!). This commit adds threading, similar to the tiled render -
it divides the light cache's voxel grid into 3d parts and renders them with the
available threads.
This makes the most significant difference on shots where the light cache pre-
process is the bottleneck, so shots with either several lights, or a high res light
cache, or both. On this file (3 lights, light cache res 120), on my Core 2 Duo it now
renders in 27 seconds compared to 49 previously.
http://mke3.net/blender/devel/rendering/volumetrics/threaded_cache.jpg
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
