On Thu, Apr 8, 2010 at 8:07 PM, Christopher Wright < [email protected]> wrote:
> > Is there a particular reason why using the example GLSL Vertex Shader > (10.5 Developer Examples), fps severely drops when attempting to shade > objects that are being rendered in a GL wireframe or GL Point mode (I've > tested this with stock Apple code as well as two common 3rd party plugins)? > Is the processing hit a bug or leak, or totally expected? Vertex shading > seems especially pricey in QC. > > Line drawing isn't particularly well-optimized in gl these days (you can > test rendering wireframes without vertex shading at all, and see a > performance hit on even the newest of cards, despite touching very few > pixels at all). Points typically aren't too slow, but they can have other > quirks. Sometimes, mismatched modes (front faces are filled, back faces are > wireframe, or the opposite) will incur an even bigger hit (perhaps because > the GPU has to potentially switch modes for every triangle?) > That makes sense, and I've noted that before. > > Vertex and Fragment shading in QC don't really do much massaging, and it's > render-mode agnostic (it doesn't know or care if you're rendering points, > lines, filled polys, etc), so there shouldn't be any performance > inconsistencies there -- if you find a composition where that's not the > case, I'd be interested to know about it (it's possible that vertex shading > is taking place in software, which would of course provide a nice > performance hit -- QC has no control over that). Make sure you're not > running in Software GL mode, just in case ;) > What I note is that lines and points have worse performance than filled polys. That's where I note the big discrepancy. > > If it was a leak, it'd show up in Instruments and you'd eventually crash. > This has definitely happened, but I haven't looked at it in Instruments. > > When you say "vertex shading seems especially pricey in QC", what are you > comparing it to? > Sorry, I'm not comparing it to another engine, what I'm comparing it to is filled polygons, vs. vertex shading either lines or points. I could have phrased that more articulately. I think you are probably right on about the fact that lines aren't optimized. However, if I was to use Kineme3D and a Noise deformer, along with a wireframe mode, I would likely get WAY better performance than using GLSL Vertex Shading to get my "wiggle", so it couldn't just be the wireframe/line mode that is the issue. That, and occasional crashes with Vertex shading, have made me wonder if there is a bug somewhere. -George Toledo
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