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Comment by pmorici | Hacker News Reader

Anyone have any insight as to why Disney would build a separate rending engine when they own Pixar and could use their renderman engine?

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Because until last year when Pixar released PRMan 19 RIS, PRMan was not that good at ray tracing / path tracing - the REYES method of rendering and shading didn't scale as well for big complex scenes when global illumination and raytraced light occlusion was done.

The RSL shading language was also causing a rather large overhead of shading time as it was an interpreted language that could no longer amortise its runtime cost over a shading grid of points using SSE - in path tracing, you generally shade one point at a time per ray vertex, although you can batch them up in some cases (but without significant ray re-ordering and deferring, after the first bounce this becomes less and less useful).

Disney also use Ptex for texturing, which doesn't really like incoherent shading points, so that was another reason to put effort into doing large scale re-ordering of rays and batching them up.

The REYES algorithm isn't really the problem, you can just generate an acceleration structure and shade each shading point using ray tracing [1]. The REYES algorithm is just an algorithm that generates shading points and determines in which pixels those points are visible, it puts no restrictions on how you shade those points. The downside to mixing REYES and ray tracing is that you have to keep two representations of the geometry in memory, but that doesn't mean you can't combine the two.

The main problem with RenderMan before version 19 was that it didn't have a good acceleration structure and that you basically had to implement a path tracer in RSL on your own. Pixar wrote a path tracer in RSL for Monster's University, so Disney could have just used that. I doubt that they would write their own renderer if they could have just asked Pixar to implement a better acceleration structure in PRMan, so there were obviously different reasons too.

I think Ptex was an important reason for them to write their own renderer, as they seem to put a lot of focus on textures in their paper on the architecture of Hyperion [2]. Hyperion's architecture also allows them to use packet tracing and to load and subdivide geometry on demand, which is also really great.

[1] http://www.realtimerendering.com/resources/RTNews/html/rtnv1...

[2] https://disney-animation.s3.amazonaws.com/uploads/production...

It was the problem, because doing REYES hiding you suffer the huge "overdrawing" issue, where you need to set the shading rate per object in the scene based on its size on screen such that it doesn't get too much shading. If it had too much shading (the shading rate was too low), many more rays will be sent. And this is because REYES shades stuff before it sees if it's visible, whereas raytracing from the camera (with the raytrace hider in PRMan) only shades the points which are visible, so it scales much more on complex scenes (when GI comes into the picture - without GI REYES can cope easily as it pages everything).

This article[1] implies that there's a lot of cross-pollination with regard to computer graphics research and technology within the movie/VFX industry. So my guess is a bit of friendly competition that keeps spurring new innovation (similar to the browser wars).

[1] http://www.fxguide.com/featured/disneys-new-production-rende...

Not backed by an article, but I'd assume there's also the factor of needing a new or different capability for an upcoming project, which would prompt the technicians to try something different without affecting in-flight projects. They can always share some of Hyperion with Pixar when Pixar is at a point to change things.

This is mostly due to the two companies being run completely separately. Resources are not shared between the two because Disney Animation is unionized where Pixar is not. It can get messy when you take non union work from Pixar and use Union work at Disney Animation and vice versa.

The real answer to this is basically that the two companies aren't all that integrated, even today. At the same time, renderman was still using ray tracing as part of it's hybrid REYES architecture.

Even so, they could have made it with renderman. Presentations saying 'this wouldn't have been possible' are more marketing than reality. It was more likely to be a combination of the right time to pitch creating a new ray tracer to see how much could be gained through batching while also having a renderer they could control and make sure was modern.

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