Hi Everybody, I am also deply interested in the topic ;-).
Current VirtualProgram implementation does not complie and relink shaders and programs each time they are applied. They are only generated and linked when certain new mix of shaders is encounterd in VirtualProgram::apply and used for the first time. Then, this set of shaders and corrsponding linked gl program is cached and reused later. Exactly the same case as when new osg::Program is compiled on first use. Difference is that osg::Program can be prebuilt in GLVisitor. Theoretically we could write a code to do the same with VirtuaProgram combinations. It will be much trickier, though... Wojtek Lewandowski ----- Original Message ----- From: Robert Osfield To: OpenSceneGraph Users Sent: Thursday, February 25, 2010 10:59 AM Subject: Re: [osg-users] Shader composition Hi Lilith, On Thu, Feb 25, 2010 at 9:12 AM, Lilith Bryant <[email protected]> wrote: I highly suggest you do some benchmarking on shader compiling/link times. We investigated this a couple of years ago, and found that we couldn't avoid an output glitch (due to compile/link time) whenever we needed a new shader. I agree that performance is critical. When ever I make major changes to the OSG I do lots of benchmarking. In this specific case compilation, linking and uniform changes all have their own performance issues to be mindful of. My expectation for shader composition was that we'd need to do upfront compilation, and linking as much as possible and select between complete programs rather than dynamically doing too much actual shader composition during draw dispatch on each frame. Keeping the CPU overhead of doing selection of which program to make active is also something that I've been pondering about. Keeping this all in check is why I need to spend the time thinking about the design so deeply. Robert. I ------------------------------------------------------------------------------ _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
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