44 lines
2.2 KiB
Plaintext
44 lines
2.2 KiB
Plaintext
/**
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******************************************************************************
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* Xenia : Xbox 360 Emulator Research Project *
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******************************************************************************
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* Copyright 2022 Ben Vanik. All rights reserved. *
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* Released under the BSD license - see LICENSE in the root for more details. *
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******************************************************************************
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*/
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#ifndef XENIA_UI_SHADERS_DITHER_8BPC_XESLI_
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#define XENIA_UI_SHADERS_DITHER_8BPC_XESLI_
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#include "xesl.xesli"
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#include "noise.xesli"
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xesl_staticConst float xe_dither_8bpc_noise[] = {
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// The conversion to 8bpc in the fixed-function output-merger is done as
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// floor(saturate(color) * 255.0 + 0.5). This dithering function effectively
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// replaces that 0.5 offset, done for rounding to the nearest, with the noise.
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// To do that, first, 0.5/255 needs to be subtracted from the color, and
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// then the noise value `[0, 255/256] / 255` from xe_dither_8bpc_noise needs
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// to be added. However, due to rounding (because division by 255.0 is
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// inexact), subtracting 0.5/255 from exact 8-bit integer color values
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// (including, for instance, 1.0, or 255/255) may result in the result being
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// smaller than the original exact 8-bit value where the noise value is 0. So,
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// remapping the noise to the `[0.5/256, 255.5/256] / 255` range. Another way
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// of preventing rounding issues is doing it manually and returning only exact
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// integer 8-bit color values divided by 255, but that would assume that the
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// render target is specifically 8bpc, so it's better to avoid that in case
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// the window system, for instance, provides a 10bpc render target (for which
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// dithering is still done here for more consistency between displays, but
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// some addition precision would still be desirable).
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XeBlueNoise16x16Values0Until256(1.0 / 256.0 / 255.0,
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(-0.5 + 0.5 / 256.0) / 255.0)
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};
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float XeDitherOffset8bpc(xesl_uint2 pixel_coord) {
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pixel_coord &= 15u;
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return xe_dither_8bpc_noise[pixel_coord.y * 16u + pixel_coord.x];
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}
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#endif // XENIA_UI_SHADERS_DITHER_8BPC_XESLI_
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