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Diffstat (limited to 'servo/components/style/color/mix.rs')
| -rw-r--r-- | servo/components/style/color/mix.rs | 475 |
1 files changed, 475 insertions, 0 deletions
diff --git a/servo/components/style/color/mix.rs b/servo/components/style/color/mix.rs new file mode 100644 index 0000000000..455d025265 --- /dev/null +++ b/servo/components/style/color/mix.rs @@ -0,0 +1,475 @@ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at https://mozilla.org/MPL/2.0/. */ + +//! Color mixing/interpolation. + +use super::{AbsoluteColor, ColorComponents, ColorFlags, ColorSpace}; +use crate::parser::{Parse, ParserContext}; +use cssparser::Parser; +use std::fmt::{self, Write}; +use style_traits::{CssWriter, ParseError, ToCss}; + +/// A hue-interpolation-method as defined in [1]. +/// +/// [1]: https://drafts.csswg.org/css-color-4/#typedef-hue-interpolation-method +#[derive( + Clone, + Copy, + Debug, + Eq, + MallocSizeOf, + Parse, + PartialEq, + ToAnimatedValue, + ToComputedValue, + ToCss, + ToResolvedValue, + ToShmem, +)] +#[repr(u8)] +pub enum HueInterpolationMethod { + /// https://drafts.csswg.org/css-color-4/#shorter + Shorter, + /// https://drafts.csswg.org/css-color-4/#longer + Longer, + /// https://drafts.csswg.org/css-color-4/#increasing + Increasing, + /// https://drafts.csswg.org/css-color-4/#decreasing + Decreasing, + /// https://drafts.csswg.org/css-color-4/#specified + Specified, +} + +/// https://drafts.csswg.org/css-color-4/#color-interpolation-method +#[derive( + Clone, + Copy, + Debug, + Eq, + MallocSizeOf, + PartialEq, + ToShmem, + ToAnimatedValue, + ToComputedValue, + ToResolvedValue, +)] +#[repr(C)] +pub struct ColorInterpolationMethod { + /// The color-space the interpolation should be done in. + pub space: ColorSpace, + /// The hue interpolation method. + pub hue: HueInterpolationMethod, +} + +impl ColorInterpolationMethod { + /// Returns the srgb interpolation method. + pub const fn srgb() -> Self { + Self { + space: ColorSpace::Srgb, + hue: HueInterpolationMethod::Shorter, + } + } + + /// Return the oklab interpolation method used for default color + /// interpolcation. + pub const fn oklab() -> Self { + Self { + space: ColorSpace::Oklab, + hue: HueInterpolationMethod::Shorter, + } + } + + /// Decides the best method for interpolating between the given colors. + /// https://drafts.csswg.org/css-color-4/#interpolation-space + pub fn best_interpolation_between(left: &AbsoluteColor, right: &AbsoluteColor) -> Self { + // The preferred color space to use for interpolating colors is Oklab. + // However, if either of the colors are in legacy rgb(), hsl() or hwb(), + // then interpolation is done in sRGB. + if !left.is_legacy_color() || !right.is_legacy_color() { + Self::oklab() + } else { + Self::srgb() + } + } +} + +impl Parse for ColorInterpolationMethod { + fn parse<'i, 't>( + _: &ParserContext, + input: &mut Parser<'i, 't>, + ) -> Result<Self, ParseError<'i>> { + input.expect_ident_matching("in")?; + let space = ColorSpace::parse(input)?; + // https://drafts.csswg.org/css-color-4/#hue-interpolation + // Unless otherwise specified, if no specific hue interpolation + // algorithm is selected by the host syntax, the default is shorter. + let hue = if space.is_polar() { + input + .try_parse(|input| -> Result<_, ParseError<'i>> { + let hue = HueInterpolationMethod::parse(input)?; + input.expect_ident_matching("hue")?; + Ok(hue) + }) + .unwrap_or(HueInterpolationMethod::Shorter) + } else { + HueInterpolationMethod::Shorter + }; + Ok(Self { space, hue }) + } +} + +impl ToCss for ColorInterpolationMethod { + fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result + where + W: Write, + { + dest.write_str("in ")?; + self.space.to_css(dest)?; + if self.hue != HueInterpolationMethod::Shorter { + dest.write_char(' ')?; + self.hue.to_css(dest)?; + dest.write_str(" hue")?; + } + Ok(()) + } +} + +/// Mix two colors into one. +pub fn mix( + interpolation: ColorInterpolationMethod, + left_color: &AbsoluteColor, + mut left_weight: f32, + right_color: &AbsoluteColor, + mut right_weight: f32, + normalize_weights: bool, +) -> AbsoluteColor { + // https://drafts.csswg.org/css-color-5/#color-mix-percent-norm + let mut alpha_multiplier = 1.0; + if normalize_weights { + let sum = left_weight + right_weight; + if sum != 1.0 { + let scale = 1.0 / sum; + left_weight *= scale; + right_weight *= scale; + if sum < 1.0 { + alpha_multiplier = sum; + } + } + } + + mix_in( + interpolation.space, + left_color, + left_weight, + right_color, + right_weight, + interpolation.hue, + alpha_multiplier, + ) +} + +/// What the outcome of each component should be in a mix result. +#[derive(Clone, Copy)] +#[repr(u8)] +enum ComponentMixOutcome { + /// Mix the left and right sides to give the result. + Mix, + /// Carry the left side forward to the result. + UseLeft, + /// Carry the right side forward to the result. + UseRight, + /// The resulting component should also be none. + None, +} + +impl ComponentMixOutcome { + fn from_colors( + left: &AbsoluteColor, + right: &AbsoluteColor, + flags_to_check: ColorFlags, + ) -> Self { + match ( + left.flags.contains(flags_to_check), + right.flags.contains(flags_to_check), + ) { + (true, true) => Self::None, + (true, false) => Self::UseRight, + (false, true) => Self::UseLeft, + (false, false) => Self::Mix, + } + } +} + +fn mix_in( + color_space: ColorSpace, + left_color: &AbsoluteColor, + left_weight: f32, + right_color: &AbsoluteColor, + right_weight: f32, + hue_interpolation: HueInterpolationMethod, + alpha_multiplier: f32, +) -> AbsoluteColor { + let outcomes = [ + ComponentMixOutcome::from_colors(left_color, right_color, ColorFlags::C1_IS_NONE), + ComponentMixOutcome::from_colors(left_color, right_color, ColorFlags::C2_IS_NONE), + ComponentMixOutcome::from_colors(left_color, right_color, ColorFlags::C3_IS_NONE), + ComponentMixOutcome::from_colors(left_color, right_color, ColorFlags::ALPHA_IS_NONE), + ]; + + // Convert both colors into the interpolation color space. + let left = left_color.to_color_space(color_space); + let left = left.raw_components(); + + let right = right_color.to_color_space(color_space); + let right = right.raw_components(); + + let (result, result_flags) = interpolate_premultiplied( + &left, + left_weight, + &right, + right_weight, + color_space.hue_index(), + hue_interpolation, + &outcomes, + ); + + let alpha = if alpha_multiplier != 1.0 { + result[3] * alpha_multiplier + } else { + result[3] + }; + + // FIXME: In rare cases we end up with 0.999995 in the alpha channel, + // so we reduce the precision to avoid serializing to + // rgba(?, ?, ?, 1). This is not ideal, so we should look into + // ways to avoid it. Maybe pre-multiply all color components and + // then divide after calculations? + let alpha = (alpha * 1000.0).round() / 1000.0; + + let mut result = AbsoluteColor::new( + color_space, + ColorComponents(result[0], result[1], result[2]), + alpha, + ); + + result.flags = result_flags; + // If both sides are legacy RGB, then the result stays in legacy RGB. + if !left_color.is_legacy_color() || !right_color.is_legacy_color() { + result.flags.insert(ColorFlags::AS_COLOR_FUNCTION); + } + + result +} + +fn interpolate_premultiplied_component( + left: f32, + left_weight: f32, + left_alpha: f32, + right: f32, + right_weight: f32, + right_alpha: f32, +) -> f32 { + left * left_weight * left_alpha + right * right_weight * right_alpha +} + +// Normalize hue into [0, 360) +#[inline] +fn normalize_hue(v: f32) -> f32 { + v - 360. * (v / 360.).floor() +} + +fn adjust_hue(left: &mut f32, right: &mut f32, hue_interpolation: HueInterpolationMethod) { + // Adjust the hue angle as per + // https://drafts.csswg.org/css-color/#hue-interpolation. + // + // If both hue angles are NAN, they should be set to 0. Otherwise, if a + // single hue angle is NAN, it should use the other hue angle. + if left.is_nan() { + if right.is_nan() { + *left = 0.; + *right = 0.; + } else { + *left = *right; + } + } else if right.is_nan() { + *right = *left; + } + + if hue_interpolation == HueInterpolationMethod::Specified { + // Angles are not adjusted. They are interpolated like any other + // component. + return; + } + + *left = normalize_hue(*left); + *right = normalize_hue(*right); + + match hue_interpolation { + // https://drafts.csswg.org/css-color/#shorter + HueInterpolationMethod::Shorter => { + let delta = *right - *left; + + if delta > 180. { + *left += 360.; + } else if delta < -180. { + *right += 360.; + } + }, + // https://drafts.csswg.org/css-color/#longer + HueInterpolationMethod::Longer => { + let delta = *right - *left; + if 0. < delta && delta < 180. { + *left += 360.; + } else if -180. < delta && delta < 0. { + *right += 360.; + } + }, + // https://drafts.csswg.org/css-color/#increasing + HueInterpolationMethod::Increasing => { + if *right < *left { + *right += 360.; + } + }, + // https://drafts.csswg.org/css-color/#decreasing + HueInterpolationMethod::Decreasing => { + if *left < *right { + *left += 360.; + } + }, + HueInterpolationMethod::Specified => unreachable!("Handled above"), + } +} + +fn interpolate_hue( + mut left: f32, + left_weight: f32, + mut right: f32, + right_weight: f32, + hue_interpolation: HueInterpolationMethod, +) -> f32 { + adjust_hue(&mut left, &mut right, hue_interpolation); + left * left_weight + right * right_weight +} + +struct InterpolatedAlpha { + /// The adjusted left alpha value. + left: f32, + /// The adjusted right alpha value. + right: f32, + /// The interpolated alpha value. + interpolated: f32, + /// Whether the alpha component should be `none`. + is_none: bool, +} + +fn interpolate_alpha( + left: f32, + left_weight: f32, + right: f32, + right_weight: f32, + outcome: ComponentMixOutcome, +) -> InterpolatedAlpha { + // <https://drafts.csswg.org/css-color-4/#interpolation-missing> + let mut result = match outcome { + ComponentMixOutcome::Mix => { + let interpolated = left * left_weight + right * right_weight; + InterpolatedAlpha { + left, + right, + interpolated, + is_none: false, + } + }, + ComponentMixOutcome::UseLeft => InterpolatedAlpha { + left, + right: left, + interpolated: left, + is_none: false, + }, + ComponentMixOutcome::UseRight => InterpolatedAlpha { + left: right, + right, + interpolated: right, + is_none: false, + }, + ComponentMixOutcome::None => InterpolatedAlpha { + left: 1.0, + right: 1.0, + interpolated: 0.0, + is_none: true, + }, + }; + + // Clip all alpha values to [0.0..1.0]. + result.left = result.left.clamp(0.0, 1.0); + result.right = result.right.clamp(0.0, 1.0); + result.interpolated = result.interpolated.clamp(0.0, 1.0); + + result +} + +fn interpolate_premultiplied( + left: &[f32; 4], + left_weight: f32, + right: &[f32; 4], + right_weight: f32, + hue_index: Option<usize>, + hue_interpolation: HueInterpolationMethod, + outcomes: &[ComponentMixOutcome; 4], +) -> ([f32; 4], ColorFlags) { + let alpha = interpolate_alpha(left[3], left_weight, right[3], right_weight, outcomes[3]); + let mut flags = if alpha.is_none { + ColorFlags::ALPHA_IS_NONE + } else { + ColorFlags::empty() + }; + + let mut result = [0.; 4]; + + for i in 0..3 { + match outcomes[i] { + ComponentMixOutcome::Mix => { + let is_hue = hue_index == Some(i); + result[i] = if is_hue { + normalize_hue(interpolate_hue( + left[i], + left_weight, + right[i], + right_weight, + hue_interpolation, + )) + } else { + let interpolated = interpolate_premultiplied_component( + left[i], + left_weight, + alpha.left, + right[i], + right_weight, + alpha.right, + ); + + if alpha.interpolated == 0.0 { + interpolated + } else { + interpolated / alpha.interpolated + } + }; + }, + ComponentMixOutcome::UseLeft => result[i] = left[i], + ComponentMixOutcome::UseRight => result[i] = right[i], + ComponentMixOutcome::None => { + result[i] = 0.0; + match i { + 0 => flags.insert(ColorFlags::C1_IS_NONE), + 1 => flags.insert(ColorFlags::C2_IS_NONE), + 2 => flags.insert(ColorFlags::C3_IS_NONE), + _ => unreachable!(), + } + }, + } + } + result[3] = alpha.interpolated; + + (result, flags) +} |