Paul Berry <stereotype...@gmail.com> writes: > On 16 May 2013 11:44, Anuj Phogat <anuj.pho...@gmail.com> wrote: > >> This patch enables ext_framebuffer_multisample_blit_scaled extension >> on intel h/w >= gen6. >> >> Note: Patches for piglit tests to verify this functionality are out >> for review on piglit mailing list. Tests pass for all of the scaling >> factors from 0.1 to 2.4. >> >> Comment from Paul Berry: >> I have some concerns about the image quality of the method you've >> implemented. As I understand it, the primary use case of this extension >> is to allow the client to do multisampled rendering at slightly less >> than screen resolution (e.g. 720p instead of 1080p), and then blit the >> result to the screen in one step while keeping most of the quality >> benefits of multisampling. Since your implementation is effectively >> equivalent to downsampling and then blitting using GL_NEAREST filtering, >> my fear is that it will lead to blocky artifacts that are severe enough >> to negate the benefit of multisampling in the first place. >> >> Before we turn this extension on in the Intel driver, I'd like to look >> at a comparison of: >> >> (1) your technique >> (2) downsampling followed by scaling with GL_LINEAR filtering >> (3) The nVidia implementation, in GL_SCALED_RESOLVE_FASTEST_EXT mode >> (4) The nVidia implementation, in GL_SCALED_RESOLVE_NICEST_EXT mode >> (5) Just rendering the image directly to the single-sampled destination >> buffer >> >> Observation: Image quality is better in cases 2, 3, 4 and 5 as >> compared to case 1. Although extension's implementation meets the >> specification's requirements, using it leads to blocky artifacts >> due to nearest filtering. >> >> I'll work on implementing a better filtering technique in blorp. >> > > Thanks for quoting my comment here. It's good to have context so that we > can continue the discussion. > > My preference would be to go ahead and land patches 1-3 now, but hold patch > 4 back until we've figured out how to get comparable image quality to the > nVidia implementation. It seems like it would be nice to go out of the > gate with our best looking implementation. > > Does that seem reasonable to other folks?
Yeah, I don't think should ship a nearest-filtered-only implementation.
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