4 ms·

Ray tracing enjoys a ridiculous amount of inherent parallelism. That's not much of an advantage though, since rasterisers also enjoy a ridiculous amount of inhe

by gsg 14y ago

Ray tracing enjoys a ridiculous amount of inherent parallelism. That's not much of an advantage though, since rasterisers also enjoy a ridiculous amount of inherent parallelism. Large scale "render farms" that exploit both already exist and are in commercial use in the VFX industry.

danwills 14y ago
I work in the VFX industry, and I agree. We often need to make a choice between a rasterisation-like method - which in VFX usually means micropolygon rendering like Pixar's REYES algorithm - or a raytracing-based method, like SideFX Mantra's Phsically-Based-Rendering. It is also possible to hybridize the two, which usually means casting rays in order to shade micropolygons. Both approaches have their own advantages. There are some tools that allow you to render a frame quickly by using many hosts to parallelise the task. This is usually only practical when the data that generates the frame is relatively small, in other words not gigabytes of fluid simulation voxels. It's also not realtime, by any stretch! A renderfarm is usually not technologically any different to local rendering on a workstation. We generally don't parallelize across hosts within a single frame, but at least you can render lots of frames simultaneously! Another thing that doesn't seem to have been mentioned on this post is that raytracing can be accelerated massively (where applicable) by using instancing. A single object can be used many times in a scene, only differing in its transformation. This allows the geometry to be stored in ram once and re-used, incoming rays that are incident on an instance's bounding box can simply be transformed into the local space of the instance. Of course this is of no help in an extremely complex scene full of unique objects, but in practice you can make great savings (and create very complex scenes that are cheap to raytrace) this way.
- Tloewald 14y ago
  Minor note: as far as I am aware (i do not write 3d engines for a living but have written games and small 3d libraries for my own use) instancing works fine with both (all?) rendering approaches in just the same way.
  - MrScruff 14y ago
    The benefits of instancing are felt more keenly in ray tracing because of the need to keep geometry in memory. If you're just dealing with direct lighting it's very easy to load and discard geometry as required as you rasterize the frame. One you start casting secondary rays you end up having to keep more of the scene in memory in order to shade a particular surface, since the lighting contribution from other geo can't be localised.
- duaneb 14y ago
  > Another thing that doesn't seem to have been mentioned on this post is that raytracing can be accelerated massively (where applicable) by using instancing. A single object can be used many times in a scene, only differing in its transformation. This allows the geometry to be stored in ram once and re-used, incoming rays that are incident on an instance's bounding box can simply be transformed into the local space of the instance. Of course this is of no help in an extremely complex scene full of unique objects, but in practice you can make great savings (and create very complex scenes that are cheap to raytrace) this way. You're also forgetting about the flip-side. A classic benefit of scanline renderers was that a scene could be split into multiple parts, which (via a z-buffer) could then be combined without any further rendering. A raytracer, on the other hand, has to have access to the whole scene (if you consider reflections, which make culling objects essentially impossible) to calculate any given pixel sample. I don't know whether this is still an issue, but for a while it was a barrier to raytracing scenes on a Pixar level.

by gsg 14y ago

danwills 14y ago

I work in the VFX industry, and I agree. We often need to make a choice between a rasterisation-like method - which in VFX usually means micropolygon rendering like Pixar's REYES algorithm - or a raytracing-based method, like SideFX Mantra's Phsically-Based-Rendering. It is also possible to hybridize the two, which usually means casting rays in order to shade micropolygons. Both approaches have their own advantages. There are some tools that allow you to render a frame quickly by using many hosts to parallelise the task. This is usually only practical when the data that generates the frame is relatively small, in other words not gigabytes of fluid simulation voxels. It's also not realtime, by any stretch! A renderfarm is usually not technologically any different to local rendering on a workstation. We generally don't parallelize across hosts within a single frame, but at least you can render lots of frames simultaneously! Another thing that doesn't seem to have been mentioned on this post is that raytracing can be accelerated massively (where applicable) by using instancing. A single object can be used many times in a scene, only differing in its transformation. This allows the geometry to be stored in ram once and re-used, incoming rays that are incident on an instance's bounding box can simply be transformed into the local space of the instance. Of course this is of no help in an extremely complex scene full of unique objects, but in practice you can make great savings (and create very complex scenes that are cheap to raytrace) this way.

Tloewald 14y ago
Minor note: as far as I am aware (i do not write 3d engines for a living but have written games and small 3d libraries for my own use) instancing works fine with both (all?) rendering approaches in just the same way.
- MrScruff 14y ago
  The benefits of instancing are felt more keenly in ray tracing because of the need to keep geometry in memory. If you're just dealing with direct lighting it's very easy to load and discard geometry as required as you rasterize the frame. One you start casting secondary rays you end up having to keep more of the scene in memory in order to shade a particular surface, since the lighting contribution from other geo can't be localised.
duaneb 14y ago
> Another thing that doesn't seem to have been mentioned on this post is that raytracing can be accelerated massively (where applicable) by using instancing. A single object can be used many times in a scene, only differing in its transformation. This allows the geometry to be stored in ram once and re-used, incoming rays that are incident on an instance's bounding box can simply be transformed into the local space of the instance. Of course this is of no help in an extremely complex scene full of unique objects, but in practice you can make great savings (and create very complex scenes that are cheap to raytrace) this way. You're also forgetting about the flip-side. A classic benefit of scanline renderers was that a scene could be split into multiple parts, which (via a z-buffer) could then be combined without any further rendering. A raytracer, on the other hand, has to have access to the whole scene (if you consider reflections, which make culling objects essentially impossible) to calculate any given pixel sample. I don't know whether this is still an issue, but for a while it was a barrier to raytracing scenes on a Pixar level.