[Bf-cycles] Shape Key drivers - bug of sorts

Ben Dansie bendansie at hotmail.com
Sun Sep 18 06:05:45 CEST 2011

Hi all,

I couldn't remember if there was a more official/appropriate place to post about bugs yet, but I've found one in recent builds. I can't remember which build revision this became a problem with sorry. The issue is to do with viewport rendering mode and shape key drivers. When a shapekey driver (or multiple) is present, the bvh is forced to rebuild constantly when in Static, or the transformations are constantly sent to the device after the first pass with Dynamic, making a pass 1, update transform, pass 1, update transform loop of sorts. When rendering with f12, this isn't an issue.

To make a repeatable test case in a new file:

Select a suzanne in default .blend fileAdd a shape key (basis) and add another key. Don't even need to change the mesh aroundAdd a driver to that new key. Don't even need to set the driver to do anything, just add one.
Run viewport renderer - easier to test the problem with Dynamic BVH

Don't know any code to figure out what the culprit is exactly (like
 a despgraph or whatever), but it would appear that the driver being on 
the mesh is forcing the constant updates, thus forcing Cycles to 
constantly update.

I'm not trying to animate with the viewport render turned on or anything crazy like that. :) But previewing materials on a character set up for animation as an example causes the issue.

Running Windows 7 64bit with a GTX 460 (cuda), but this happens with gpu and cpu, so I doubt it is device related.

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