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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Goodbye to a nasty scaling bug</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Today I sorted out an issue that prevented going beyond 220,000 or so faces per mesh part. As the mesh size increases past that, performance first falls of a cliff by orders of magnitude, then large parts of the mesh start flashing on and off, then the whole machine becomes unresponsive. Maybe some kind of massive memory leak in kernel. Fortunately, when I kill the world engine the machine comes back to life after a while. But this is a Bad Thing[tm] by any standard. Surely I am not the only one rendering element arrays of this size on the open source OpenGL stack? </p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">OK, maybe I am, or at least it is a small club. Anyway, this morning I finally succeeded in developing a workaround after fretting about this for the last few months. Conceptually the fix is simple: when I compile a half edge mesh into OpenGL drawarrays form, I now split the mesh into parts smaller than 4 MB. This is a little messy because the splitting happens deep inside the triangle mesh compiler, which already qualifies as deeply arcane. But the patch came out small and the results are better than excellent. Now we can render multiple compiled meshes of well over a million triangles each and it's exceptionally efficient. I'm really excited about this.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Unicode character glyphs</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Another goody landed this weekend: Unicode glyph glyph support. This opens up a wealth of beautiful character outlines to exercise the new triangulation code, and just be generally lovely. I rendered some Kanji characters for Hirofumi's entertainment:</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> http://phunq.net/files/shiny85.png ('full year' kanji) </p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> http://phunq.net/files/shiny86.png ('happy' kanji)</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">The second image is over 1.5 million triangles and renders at a solid 60 FPS on this low end, fanless GPU. I haven't yet determined how high this scales, but most probably a lot higher. So breakthrough is the word for it.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Now I am happy with baseline render performance and can put that aside for a while. To recap, high performance rendering is achieved with a mesh compiler that converts from halfedge mesh form to efficient triangle strips. First we model the mesh, including possibly subdividing it, then compile it for 3D viewing. Compiling is fast, about 1 microsecond per triangle, so a million triangle mesh takes about a second to compile, after which it renders smooth as silk.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Faster, better, bigger</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Most of the mesh compile time is spent calculating vertex normals for smooth shading. There are some big optimizations possible here, without sacrificing accuracy, so down the road we may see a factor of four or more improvement at the cost of more down and dirty work on the mesh compiler. And way down the road, we might do this job on the GPU using hundreds of processors in parallel. With that, mesh compiling should be essentially instantaneous for meshes of the complexity we see here.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">For now, tricks are needed to make interactive editing operations seem fast, because even one second per frame is too slow for an artist to work comfortably . I'm starting to think now about what those tricks might be. Because editing these subdivision meshes interactively is not that far away, and that is the last major piece we need for a game designer to create a full suite of 3D mesh assets for a respectable simulation game. In an upcoming post I will talk more about the "loop modeling" approach I have in mind for organic meshes.</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Regards,</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Daniel</p>
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