vello_cpu: Add u8 fast path for some blend modes #1653
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| // Copyright 2025 the Vello Authors | ||
| // SPDX-License-Identifier: Apache-2.0 OR MIT | ||
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| use crate::fine::{Splat4thExt, highp, u8_to_f32}; | ||
| use crate::peniko::{BlendMode, Mix}; | ||
| use vello_common::fearless_simd::*; | ||
| use vello_common::util::{Div255Ext, f32_to_u8, normalized_mul_u8x32}; | ||
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| // TODO: Make sure this vectorizes properly (also the f32 pipeline) by inlining if needed. | ||
| pub(crate) fn mix<S: Simd>(src_c: u8x32<S>, bg_c: u8x32<S>, blend_mode: BlendMode) -> u8x32<S> { | ||
| if let Some(res) = try_u8_mix(blend_mode, src_c, bg_c) { | ||
| return res; | ||
| } | ||
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| // Fallback for blend modes that aren't supported in u8. | ||
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| let to_f32 = |val: u8x32<S>| { | ||
| let (a, b) = src_c.simd.split_u8x32(val); | ||
| let mut a = u8_to_f32(a); | ||
| let mut b = u8_to_f32(b); | ||
| a *= f32x16::splat(src_c.simd, 1.0 / 255.0); | ||
| b *= f32x16::splat(src_c.simd, 1.0 / 255.0); | ||
| (a, b) | ||
| }; | ||
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| let to_u8 = |val1: f32x16<S>, val2: f32x16<S>| { | ||
| let val1 = | ||
| f32_to_u8(f32x16::splat(val1.simd, 255.0).mul_add(val1, f32x16::splat(val1.simd, 0.5))); | ||
| let val2 = | ||
| f32_to_u8(f32x16::splat(val2.simd, 255.0).mul_add(val2, f32x16::splat(val2.simd, 0.5))); | ||
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| val1.simd.combine_u8x16(val1, val2) | ||
| }; | ||
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| let (mut src_1, mut src_2) = to_f32(src_c); | ||
| let (bg_1, bg_2) = to_f32(bg_c); | ||
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| src_1 = highp::blend::mix(src_1, bg_1, blend_mode); | ||
| src_2 = highp::blend::mix(src_2, bg_2, blend_mode); | ||
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| to_u8(src_1, src_2) | ||
| } | ||
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| fn try_u8_mix<S: Simd>(blend_mode: BlendMode, src_c: u8x32<S>, bg_c: u8x32<S>) -> Option<u8x32<S>> { | ||
| // We implement the u8 fast path for blend modes that | ||
| // 1) are separable. | ||
| // 2) don't have too many divisions, since integer normalization is | ||
| // relatively expensive. | ||
| // In the future, it's possible to do further experimentation to see whether | ||
| // some more blend modes are worth doing in integer space. | ||
| Some(match blend_mode.mix { | ||
| Mix::Normal => src_c, | ||
| Mix::Multiply => Multiply::mix(src_c, bg_c), | ||
| Mix::Screen => Screen::mix(src_c, bg_c), | ||
| Mix::Overlay => Overlay::mix(src_c, bg_c), | ||
| Mix::Darken => Darken::mix(src_c, bg_c), | ||
| Mix::Lighten => Lighten::mix(src_c, bg_c), | ||
| Mix::HardLight => HardLight::mix(src_c, bg_c), | ||
| Mix::Difference => Difference::mix(src_c, bg_c), | ||
| Mix::Exclusion => Exclusion::mix(src_c, bg_c), | ||
| Mix::ColorDodge | ||
| | Mix::ColorBurn | ||
| | Mix::SoftLight | ||
| | Mix::Luminosity | ||
| | Mix::Color | ||
| | Mix::Hue | ||
| | Mix::Saturation => return None, | ||
| }) | ||
| } | ||
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| macro_rules! u8_mix { | ||
| ($name:ident, $calc:expr) => { | ||
| struct $name; | ||
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| impl $name { | ||
| #[inline(always)] | ||
| fn mix<S: Simd>(src_c: u8x32<S>, bg_c: u8x32<S>) -> u8x32<S> { | ||
| let simd = src_c.simd; | ||
| let res = $calc(src_c, bg_c); | ||
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| with_src_alpha(simd, res, src_c) | ||
| } | ||
| } | ||
| }; | ||
| } | ||
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| // Formula for blending is (see https://www.w3.org/TR/compositing-1/#generalformula): | ||
| // Cs' = (1 - Ab) * Cs + Ab * B(Cb, Cs) | ||
| // Since vello_cpu expects premultiplied colors, we need to return: | ||
| // M = As * Cs' | ||
| // = As * ((1 - Ab) * Cs + Ab * B(Cb, Cs)) | ||
| // = As * (1 - Ab) * Cs + As * Ab * B(Cb, Cs) | ||
| // = S * (1 - Ab) + As * Ab * B(Cb, Cs) | ||
| // where S = As * Cs and D = Ab * Cb (so just the premultiplied color). | ||
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| // Multiply: | ||
| // B(Cb, Cs) = Cb * Cs | ||
| // M = S * (1 - Ab) + As * Ab * Cb * Cs | ||
| // = S * (1 - Ab) + S * D | ||
| u8_mix!(Multiply, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| let simd = src_c.simd; | ||
| let one_minus_bg_a = 255 - bg_c.splat_4th(); | ||
| let p1 = normalized_mul_u8x32(src_c, one_minus_bg_a); | ||
| let p2 = normalized_mul_u8x32(src_c, bg_c); | ||
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| simd.narrow_u16x32(p1 + p2) | ||
| }); | ||
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| // Screen: | ||
| // B(Cb, Cs) = Cb + Cs - Cb * Cs | ||
| // M = S * (1 - Ab) + As * D + S * Ab - S * D | ||
| // = S + As * D - S * D | ||
| u8_mix!(Screen, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| let simd = src_c.simd; | ||
| let p1 = normalized_mul_u8x32(src_c.splat_4th(), bg_c); | ||
| let p2 = normalized_mul_u8x32(src_c, bg_c); | ||
| let res = simd.widen_u8x32(src_c) + p1 - p2; | ||
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| simd.narrow_u16x32(res) | ||
| }); | ||
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| // Overlay is hard-light with source and backdrop swapped. | ||
| u8_mix!(Overlay, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| hard_light_inner(src_c, bg_c, bg_c) | ||
| }); | ||
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| // Darken: | ||
| // B(Cb, Cs) = min(Cb, Cs) | ||
| // M = S * (1 - Ab) + min(S * Ab, D * As) | ||
| u8_mix!(Darken, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| let simd = src_c.simd; | ||
| let src_a = src_c.splat_4th(); | ||
| let bg_a = bg_c.splat_4th(); | ||
| let p1 = normalized_mul_u8x32(src_c, 255 - bg_a); | ||
| let p2 = normalized_mul_u8x32(src_c, bg_a).min(normalized_mul_u8x32(bg_c, src_a)); | ||
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| simd.narrow_u16x32(p1 + p2) | ||
| }); | ||
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| // Lighten: | ||
| // B(Cb, Cs) = max(Cb, Cs) | ||
| // M = S * (1 - Ab) + max(S * Ab, D * As) | ||
| u8_mix!(Lighten, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| let simd = src_c.simd; | ||
| let src_a = src_c.splat_4th(); | ||
| let bg_a = bg_c.splat_4th(); | ||
| let p1 = normalized_mul_u8x32(src_c, 255 - bg_a); | ||
| let p2 = normalized_mul_u8x32(src_c, bg_a).max(normalized_mul_u8x32(bg_c, src_a)); | ||
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| simd.narrow_u16x32(p1 + p2) | ||
| }); | ||
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| // Hard-light: | ||
| // if Cs <= 0.5: B(Cb, Cs) = 2 * Cb * Cs | ||
| // otherwise: B(Cb, Cs) = 1 - 2 * (1 - Cb) * (1 - Cs) | ||
| u8_mix!(HardLight, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| hard_light_inner(src_c, bg_c, src_c) | ||
| }); | ||
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| // Difference: | ||
| // B(Cb, Cs) = abs(Cb - Cs) | ||
| // M = S * (1 - Ab) + abs(S * Ab - D * As) | ||
| u8_mix!(Difference, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| let simd = src_c.simd; | ||
| let src_a = src_c.splat_4th(); | ||
| let bg_a = bg_c.splat_4th(); | ||
| let p1 = normalized_mul_u8x32(src_c, 255 - bg_a); | ||
| let p2 = normalized_mul_u8x32(src_c, bg_a); | ||
| let p3 = normalized_mul_u8x32(bg_c, src_a); | ||
| let diff = p2.max(p3) - p2.min(p3); | ||
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| simd.narrow_u16x32(p1 + diff) | ||
| }); | ||
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| // Exclusion: | ||
| // B(Cb, Cs) = Cb + Cs - 2 * Cb * Cs | ||
| // M = S * (1 - Ab) + As * D + S * Ab - 2 * S * D | ||
| // = S + As * D - 2 * S * D | ||
| u8_mix!(Exclusion, |src_c: u8x32<S>, bg_c: u8x32<S>| { | ||
| let simd = src_c.simd; | ||
| let p1 = normalized_mul_u8x32(src_c.splat_4th(), bg_c); | ||
| let p2 = normalized_mul_u8x32(src_c, bg_c); | ||
| let res = simd.widen_u8x32(src_c) + p1; | ||
| let sub = p2 + p2; | ||
| let res = simd.select_u16x32(res.simd_ge(sub), res - sub, u16x32::splat(simd, 0)); | ||
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| simd.narrow_u16x32(res) | ||
| }); | ||
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| #[inline(always)] | ||
| fn hard_light_inner<S: Simd>(src_c: u8x32<S>, bg_c: u8x32<S>, condition: u8x32<S>) -> u8x32<S> { | ||
| let simd = src_c.simd; | ||
| let src = simd.widen_u8x32(src_c); | ||
| let bg = simd.widen_u8x32(bg_c); | ||
| let src_a = simd.widen_u8x32(src_c.splat_4th()); | ||
| let bg_a = simd.widen_u8x32(bg_c.splat_4th()); | ||
| let condition_a = simd.widen_u8x32(condition.splat_4th()); | ||
| let condition = simd.widen_u8x32(condition); | ||
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| let base = src * (255 - bg_a); | ||
| // Multiply branch: As * Ab * 2 * Cb * Cs = 2 * S * D. | ||
| let multiply = 2 * src * bg; | ||
| // Screen branch: As * Ab * (1 - 2 * (1 - Cb) * (1 - Cs)) | ||
| // = As * Ab - 2 * (As - S) * (Ab - D). | ||
| let screen = src_a * bg_a - 2 * (src_a - src) * (bg_a - bg); | ||
| let blended = simd.select_u16x32( | ||
| // The spec condition is `Cs <= 0.5` but on unpremultiplied color. | ||
| // Since `Cs = S / As`, we avoid division by multiplying both sides | ||
| // by alpha: `Cs <= 0.5` => `S <= 0.5 * As` => `2 * S <= As`. | ||
| (condition + condition).simd_le(condition_a), | ||
| multiply, | ||
| screen, | ||
| ); | ||
| let res = (base + blended).div_255(); | ||
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| simd.narrow_u16x32(res) | ||
| } | ||
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| #[inline(always)] | ||
| fn with_src_alpha<S: Simd>(simd: S, rgb: u8x32<S>, src_c: u8x32<S>) -> u8x32<S> { | ||
| let alpha_mask = u32x8::splat(simd, u32::from_ne_bytes([0, 0, 0, 255])).to_bytes(); | ||
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| (rgb & !alpha_mask) | (src_c & alpha_mask) | ||
| } | ||
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Would it make sense to add
#[inline(always)]here?There was a problem hiding this comment.
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Yes, but I will do this in a follow-up since we need to fix this up in a couple of places anyway (see #1579).
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Will add a TODO.