Re: [Mypaint-discuss] brushlib with GPU
On 7 October 2013 00:36, brdavs brd...@yahoo.com wrote: Hi Jon, Thank you very much for your kind reply. You are welcome. I'm keeping the mypaint-discuss mailing list CC'ed so others can follow as well. I have several questions / comments: 1. Why do you think that OpenCL is a better solution than doing it purely in OpenGL? One problem I see is that if you are drawing a lot of small dabs, OpenCL will probably be very inefficient, because you won't be doing much work for each dab. You'll be launching a kernel a lot which is not negligible. OpenCL is a more general programming model, hence it will probably be easier to translate existing code and concepts in a meaningful way. Also, I've programmed GPUs in this manner before (using CUDA) - where as I've never done non-trivial OpenGL. If one can make it work in OpenGL/GLSL, that would probably be ideal. Both from performance and availability perspective. Any ideas how to realize the algorithm there would be very welcomed! In addition to a surface backend, you will likely want a way to display the surface on screen - so that is the other thing that needs implementing. This could/should be OpenGL based, using the OpenCL+OpenGL interoperability if the surf backend is in OpenCL. For making full advantage of such a backend in MyPaint itself, one would also have to implement layers etc. on the GPU side. 2. Even if you can batch a bunch of dabs together, the dabs will overlap and you would have to resort to atomic operations (slower) for proper blending. The CPU backend has an operations queue in which dabs are batched, in a tile-wise manner. See operationsqueue.c and mypaint-tiledsurface.c No concurrency is attempted between individual dabs, ordering is preserved by the queue. Threads work on individual tiles, with no syncronization necessary between them. On the GPU one would ideally like that every (output) pixel is computed concurrently without sync. One could perhaps apply the same queuing principle, but probably use a vector for the depth - and store the queue suitable for consumption by individual thread warps (16/32 on GPUs I am used to). But, starting with the naive one-kernel-per-dab approach is probably the best. Once we have that we can think of smarter ways of doing things. 3. Is there a super simple working example of the brushlib painting a (hardwired) stroke with a configurable brush? I would be interested in trying a few simple things in OpenCL (no tiling, etc.) and would be good to have a simple starting point in C/C++ and a reference implementation. Sadly the minimal.c example is broken right now. The API usage as shown is fine, its just the simple surface that is borked - wrong buffer stride handling in the backend. I will have a look at fixing it up later, but I would not wait for it. For GPU things, you'll need a lot of additional scaffolding (OpenCL setup etc), so maybe copy minimal.c and start adding that. I suggest you put the code in a subdirectory as it will have extra dependencies, for instance brushlib/cl/. BlackInk seems to have a very impressive paint engine inplemented on the GPU: http://www.bleank.com/BlackInk-a115.html Marko -- Jon Nordby - www.jonnor.com ___ Mypaint-discuss mailing list Mypaint-discuss@gna.org https://mail.gna.org/listinfo/mypaint-discuss
Re: [Mypaint-discuss] brushlib with GPU
If I could suggest, using OpenGL ES instead of OpenGL should make it more portable. Most platform hardware accelerate OpenGL ES, only few accelerate OpenGL. This is a video comparaison on the cubieboard2 (finally managed to use HDMI-dvi output, recorded with a camera), at the left glmark (OpenGL), at the right glmark_es2 (OpenGL ES): I don't think every advanced functions of OpenGL are needed in the case of MyPaint. http://popolon.org/cubieboard/demos_video.201310/glmark_glmark-es.720.m4v OpenVG is another solution, as everything is 2D vector graphic in mypaint. LibEGL is the common interface for both: http://www.khronos.org/egl/ Regards, Popolon Le 2013-10-05 14:02, Jon Nordby a écrit : Hi Marko, I do not know if anyone has actually tried to implement a GPU backend - but it is something I've given quite a bit of thought. The idea is briefly documented in brushlib/PERFORMANCE https://gitorious.org/mypaint/mypaint/source/master:brushlib/PERFORMANCE Blending of the dab onto the surface is the responsibility of the MyPaintSurface backend. For the normal CPU tiled version, that code is found in brushlib/mypaint-tiled-surface.c and brushlib/brushmodes.c. Search for draw_dab_pixels_ In addition to a surface backend, you will likely want a way to display the surface on screen - so that is the other thing that needs implementing. This could/should be OpenGL based, using the OpenCL+OpenGL interoperability if the surf backend is in OpenCL. For making full advantage of such a backend in MyPaint itself, one would also have to implement layers etc. on the GPU side. On 4 October 2013 23:30, brdavs brd...@yahoo.com wrote: Hi, I have been browsing through brush engine in mypaint. I am wondering if anybody has tried to implement the backend in OpenGL/OpenCL. If I understand correctly, the only thing that is needed to get brush engine working is to implement GPU-backed MyPaintSurface with appropriate methods. Correct? One thing that is not immediately obvious to me is where does blending occur. Namely, when you draw a dab where does the blending occur? It seems that one would want that to be done on the GPU as well. Is there anything else that would have to be rewritten to take advantage of the GPU? Thanks, Marko ___ Mypaint-discuss mailing list Mypaint-discuss@gna.org https://mail.gna.org/listinfo/mypaint-discuss
Re: [Mypaint-discuss] brushlib with GPU
Hi Marko, I do not know if anyone has actually tried to implement a GPU backend - but it is something I've given quite a bit of thought. The idea is briefly documented in brushlib/PERFORMANCE https://gitorious.org/mypaint/mypaint/source/master:brushlib/PERFORMANCE Blending of the dab onto the surface is the responsibility of the MyPaintSurface backend. For the normal CPU tiled version, that code is found in brushlib/mypaint-tiled-surface.c and brushlib/brushmodes.c. Search for draw_dab_pixels_ In addition to a surface backend, you will likely want a way to display the surface on screen - so that is the other thing that needs implementing. This could/should be OpenGL based, using the OpenCL+OpenGL interoperability if the surf backend is in OpenCL. For making full advantage of such a backend in MyPaint itself, one would also have to implement layers etc. on the GPU side. On 4 October 2013 23:30, brdavs brd...@yahoo.com wrote: Hi, I have been browsing through brush engine in mypaint. I am wondering if anybody has tried to implement the backend in OpenGL/OpenCL. If I understand correctly, the only thing that is needed to get brush engine working is to implement GPU-backed MyPaintSurface with appropriate methods. Correct? One thing that is not immediately obvious to me is where does blending occur. Namely, when you draw a dab where does the blending occur? It seems that one would want that to be done on the GPU as well. Is there anything else that would have to be rewritten to take advantage of the GPU? Thanks, Marko -- Jon Nordby - www.jonnor.com ___ Mypaint-discuss mailing list Mypaint-discuss@gna.org https://mail.gna.org/listinfo/mypaint-discuss
