That's an interesting idea! llvmpipe rasterization is complicated and very optimized, so changing llvmpipe's rasterizer to spit out MSAA coverages is very hard. I think that a good way to approach this is to:
1) continue to do single sample rasterization, but adjust the line coeffs of the triangles edges (in llvmpipe rasterizer code known as plane coefficients) to do conservative rasterization (ie, so that any fragment that intersects a triangle is covered) when MSAA is enabled. See https://developer.nvidia.com/content/dont-be-conservative-conservative-rasterization 2) once inside the fragment shader, compute SampleMaskIn from the unadjusted vertex positions, using the desired number of samples (and corresponding sample pattern) None of this would be throwaway work: the SampleMaskIn are correct and could be used for full MSAA support in the future too, and the conservative rasterization could be a feature on its own right too eventually. Jose ________________________________ From: mesa-dev <mesa-dev-boun...@lists.freedesktop.org> on behalf of Marek Olšák <mar...@gmail.com> Sent: Wednesday, January 6, 2021 05:57 To: Brian Paul <bri...@vmware.com> Cc: mesa-dev@lists.freedesktop.org <mesa-dev@lists.freedesktop.org>; mesa-us...@lists.freedesktop.org <mesa-us...@lists.freedesktop.org> Subject: Re: [Mesa-dev] Fwd: [Mesa-users] Issues with removal of classic OSMesa Hi, llvmpipe could implement line and polygon smoothing by rasterizing in MSAA and passing the coverage to SampleMaskIn in the fragment shader, but doing Z/S tests and color writes and everything else single-sampled. Then, FragColor.a *= bitcount(SampleMaskIn) / (float)num_samples. It's roughly what OpenGL requires. There is at least one other gallium driver that does that. Marek On Mon, Jan 4, 2021 at 3:02 PM Brian Paul <bri...@vmware.com<mailto:bri...@vmware.com>> wrote: Hi Andreas, I'm forwarding your message to the mesa-dev list for better visibility. BTW, when you say "antialiasing" below, what exactly do you mean? -Brian -------- Forwarded Message -------- Subject: [Mesa-users] Issues with removal of classic OSMesa Date: Thu, 31 Dec 2020 12:56:04 +0100 From: Andreas Fänger <a.faen...@e-sign.com<mailto:a.faen...@e-sign.com>> To: mesa-us...@lists.freedesktop.org<mailto:mesa-us...@lists.freedesktop.org> Hi, I've just seen that classic OSMesa has been removed (again) from Mesa3D a few weeks ago with this commit "mesa: Retire classic OSMesa". We are still actively using classical OSMesa for high quality rendering of still images in a headless environment with no GPU support (server-based rendering on windows and linux) Unfortunately, none of the alternative software renderers provide all the features that we require, which is antialiasing and anisotropic filtering. The current state is (correct me if I'm wrong) * softpipe: anisotropic filtering is supported, no antialiasing * llvmpipe: no anisotropic filtering, has MSAA * openswr: no anisotropic filtering, has MSAA, no OSMesa interface (?) We had hoped that classical OSMesa is only removed when there is a full replacement after the discussions in 2016 when OSMesa was about to be removed for the first time https://lists.freedesktop.org/archives/mesa-dev/2016-March/109665.html<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Farchives%2Fmesa-dev%2F2016-March%2F109665.html&data=04%7C01%7Cjfonseca%40vmware.com%7C38811048f7d4434b32cc08d8b208137f%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637455095057094583%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=HjIWy%2B4Mip6TkKYWUEuix41bPSgHUzZqgzwnBnjtBWA%3D&reserved=0> https://lists.freedesktop.org/archives/mesa-users/2016-March/001132.html<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Farchives%2Fmesa-users%2F2016-March%2F001132.html&data=04%7C01%7Cjfonseca%40vmware.com%7C38811048f7d4434b32cc08d8b208137f%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637455095057094583%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=nSZ3ZSfFRt8Z06avVzILOg4TipMkZ9CLyGMONcOkZxk%3D&reserved=0> and the commit that reverted the removal http://cgit.freedesktop.org/mesa/mesa/commit/?id=9601815b4be886f4d92bf74916de98f3bdb7275c<https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fcgit.freedesktop.org%2Fmesa%2Fmesa%2Fcommit%2F%3Fid%3D9601815b4be886f4d92bf74916de98f3bdb7275c&data=04%7C01%7Cjfonseca%40vmware.com%7C38811048f7d4434b32cc08d8b208137f%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637455095057104572%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=DufgWCKsN0v1nvTnT9VmyRkTSWiksioEYKIabLO%2BDvI%3D&reserved=0> Are there any plans to enhance the renderers so that at least one of them is providing both anisotropic filtering and antialiasing? As far as I know, anisotropic texture filtering is also one of the OpenGL 4.6 requirements. In 2016 I was told that there are only very few developers involved in llvmpipe and that chances are not high that someone is going to port the softpipe anisotropic filtering implementation as llvmpipe is much more complex. Is there any change in that situation? If there are no such plans, is there any chance of reverting this commit again so that classical OSMesa is available for windows and linux in mesa >20? Regards, Andreas Fänger _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org<mailto:mesa-dev@lists.freedesktop.org> https://lists.freedesktop.org/mailman/listinfo/mesa-dev<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Fmailman%2Flistinfo%2Fmesa-dev&data=04%7C01%7Cjfonseca%40vmware.com%7C38811048f7d4434b32cc08d8b208137f%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637455095057104572%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=kU2Sz0FyTbVjirPOPsjm6hGVjJJuLg5qeCB93NnNuJk%3D&reserved=0>
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