Doom9's Forum - View Single Post - Video player Shaders guide (MPC-HC, mpc-BE, mpv)

butterw2 · 22nd July 2020, 17:44

Linear sampling is a performance optimization technique for gpu pixel shader. The idea is to reduce the number of pixel (texture) fetches required by an algorithm by sampling between pixels and exploiting hardware linear interpolation.

a 2-pass pre-resize shader test was performed:
https://github.com/butterw/bShaders/...linearSampling
- pass-1 generate a black and white stripe test motif,
- pass-2 use linear sampling

Expected: interpolation, colored Red
Result: no interpolation (Nearest Neighbor). If the offset is set to 0.5 pixel: produces some rounding artefacts !

Software and hardware setup
- mpc-hc v1.9.6 + EVR-CP. Also tested in mpc-be
- old intel igpu (hd4400), not the latest Win10 + drivers

## Linear Sampling (in hlsl): tex2D(s0, tex + k*p1) where k is non integer
the effect of Nearest Neighbor sampling is to round k.x, k.y to the nearest integer. If k.x or k.y is a half, you then get some rounding artefacts.
While it certainly is possible to get rid of the rounding artefacts, they are a symptom of the larger problem: Linear Sampling not being supported, which has major implications for the math analysis.

Linear sampling is exploited by perf optimized convolution kernel shaders (such as: Luma Sharpen, gaussian blur, etc.). If it isn't supported, the shaders still produce an output, but a suboptimal one. The provided test allows for the user to test whether linear sampling is actually supported.

Edit (linear sampling works in mpv): the same test using rgb32 png input was performed on the same configuration with a glsl shader (mpv video player, vo=gpu), and I'm getting the expected result there !
https://github.com/butterw/bShaders/...linearSampling

Edit2 (hw linear sampling isn't supported in mpc-hc/be): hw linear sampling also not working as expected in mpc-hc/be with mpc-vr as video renderer in dx9 and dx11 modes.
https://github.com/clsid2/mpc-hc/issues/748
This impacts shaders such as LumaSharpen.hlsl

22nd July 2020, 17:44	#6 \| Link
butterw2 Registered User Join Date: Jun 2020 Posts: 303	# mpc-hc/be don't support hw linear sampling Linear sampling is a performance optimization technique for gpu pixel shader. The idea is to reduce the number of pixel (texture) fetches required by an algorithm by sampling between pixels and exploiting hardware linear interpolation. a 2-pass pre-resize shader test was performed: https://github.com/butterw/bShaders/...linearSampling - pass-1 generate a black and white stripe test motif, - pass-2 use linear sampling Expected: interpolation, colored Red Result: no interpolation (Nearest Neighbor). If the offset is set to 0.5 pixel: produces some rounding artefacts ! Software and hardware setup - mpc-hc v1.9.6 + EVR-CP. Also tested in mpc-be - old intel igpu (hd4400), not the latest Win10 + drivers ## Linear Sampling (in hlsl): tex2D(s0, tex + kp1) where k is non integer the effect of Nearest Neighbor sampling is to round k.x, k.y to the nearest integer. If k.x or k.y is a half, you then get some rounding artefacts. While it certainly is possible to get rid of the rounding artefacts, they are a symptom of the larger problem: Linear Sampling not being supported, which has major implications for the math analysis. Linear sampling is exploited by perf optimized convolution kernel shaders (such as: Luma Sharpen, gaussian blur, etc.). If it isn't supported, the shaders still produce an output, but a suboptimal one. The provided test allows for the user to test whether linear sampling is actually supported. Edit (linear sampling works in mpv):* the same test using rgb32 png input was performed on the same configuration with a glsl shader (mpv video player, vo=gpu), and I'm getting the expected result there ! https://github.com/butterw/bShaders/...linearSampling Edit2 (hw linear sampling isn't supported in mpc-hc/be): hw linear sampling also not working as expected in mpc-hc/be with mpc-vr as video renderer in dx9 and dx11 modes. https://github.com/clsid2/mpc-hc/issues/748 This impacts shaders such as LumaSharpen.hlsl __________________ bShaders: realtime Effects/filters for video players Last edited by butterw2; 26th March 2021 at 10:51. Reason: Works as expected in mpv !