feat: Implement contrast-color function #808
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -1038,6 +1038,9 @@ fn parse_color_function<'i, 't>( | |
| "rgb" | "rgba" => { | ||
| parse_rgb(input, &mut parser) | ||
| }, | ||
| "contrast-color" => { | ||
| input.parse_nested_block(parse_contrast_color) | ||
| }, | ||
| "color-mix" => { | ||
| input.parse_nested_block(parse_color_mix) | ||
| }, | ||
|
|
@@ -1630,6 +1633,21 @@ impl RGBA { | |
| pub fn alpha_f32(&self) -> f32 { | ||
| self.alpha as f32 / 255.0 | ||
| } | ||
|
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||
| /// Returns the [relative luminance](https://www.w3.org/TR/WCAG21/#dfn-relative-luminance) of the color. | ||
| fn relative_luminance(&self) -> f32 { | ||
| fn channel_luminance(channel: f32) -> f32 { | ||
| if channel <= 0.04045 { | ||
| channel / 12.92 | ||
| } else { | ||
| ((channel + 0.055) / 1.055).powf(2.4) | ||
| } | ||
| } | ||
|
|
||
| 0.2126 * channel_luminance(self.red_f32()) | ||
| + 0.7152 * channel_luminance(self.green_f32()) | ||
| + 0.0722 * channel_luminance(self.blue_f32()) | ||
| } | ||
| } | ||
|
|
||
| fn clamp_unit_f32(val: f32) -> u8 { | ||
|
|
@@ -3134,6 +3152,105 @@ where | |
| current.into() | ||
| } | ||
|
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| fn calculate_contrast_color(base_luminance: f32, mut candidates: Vec<CssColor>) -> CssColor { | ||
| if candidates.is_empty() { | ||
| candidates.push(CssColor::RGBA(RGBA::new(0, 0, 0, 1.0))); | ||
| candidates.push(CssColor::RGBA(RGBA::new(255, 255, 255, 1.0))); | ||
| } | ||
|
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||
| fn wcag2_contrast_ratio(l1: f32, l2: f32) -> f32 { | ||
| // https://www.w3.org/TR/WCAG21/#dfn-contrast-ratio | ||
| let l1 = l1 + 0.05; | ||
| let l2 = l2 + 0.05; | ||
|
|
||
| if l1 > l2 { | ||
| l1 / l2 | ||
| } else { | ||
| l2 / l1 | ||
| } | ||
| } | ||
|
|
||
| let mut best_contrast = 0.0; | ||
| let mut best_contrast_index = 0; | ||
|
|
||
| for (i, candidate) in candidates.iter().enumerate() { | ||
| let candidate_luminance = candidate.relative_luminance().unwrap(); | ||
| let contrast = wcag2_contrast_ratio(base_luminance, candidate_luminance); | ||
|
|
||
| if contrast > best_contrast { | ||
| best_contrast = contrast; | ||
| best_contrast_index = i; | ||
| } | ||
| } | ||
|
|
||
| candidates[best_contrast_index].clone() | ||
| } | ||
|
|
||
| fn parse_contrast_color<'i, 't>(input: &mut Parser<'i, 't>) -> Result<CssColor, ParseError<'i, ParserError<'i>>> { | ||
| let base_color = CssColor::parse(input)?; | ||
|
|
||
| let base_luminance = match base_color.relative_luminance() { | ||
| Some(value) => value, | ||
| None => { | ||
| return Err(input.new_custom_error(ParserError::InvalidValue)); | ||
| } | ||
| }; | ||
|
|
||
| let location = input.current_source_location(); | ||
|
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||
| match input.expect_ident() { | ||
| Ok(value) => { | ||
| match_ignore_ascii_case! { value, | ||
| // https://drafts.csswg.org/css-color-5/#contrast-color | ||
| "max" => { | ||
| return Ok(calculate_contrast_color(base_luminance, Vec::new())); | ||
| }, | ||
|
|
||
| // https://github.com/w3c/csswg-drafts/issues/7937 | ||
| #[cfg(feature = "level6")] | ||
| "tbd-bg" | "tbd-fg" => { | ||
| input.expect_ident_matching("wcag2")?; | ||
|
There was a problem hiding this comment. Looks like this is optional in the spec.
Also looks like it can be a function:
|
||
| input.expect_comma()?; | ||
|
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||
| let mut candidates = Vec::new(); | ||
|
|
||
| loop { | ||
| let color = CssColor::parse(input)?; | ||
|
|
||
| if color.relative_luminance().is_none() { | ||
| break Err(input.new_custom_error(ParserError::InvalidValue)); | ||
| } | ||
|
|
||
| candidates.push(color); | ||
|
|
||
| match input.expect_comma() { | ||
| Ok(()) => {} | ||
|
|
||
| Err(BasicParseError { | ||
| kind: BasicParseErrorKind::EndOfInput, | ||
| .. | ||
| }) => break Ok(calculate_contrast_color(base_luminance, candidates)), | ||
|
|
||
| Err(e) => break Err(e.into()), | ||
| } | ||
| } | ||
| }, | ||
|
|
||
| _ => { | ||
| Err(location.new_unexpected_token_error(Token::Ident(value.to_owned()))) | ||
| } | ||
| } | ||
| } | ||
|
|
||
| Err(BasicParseError { | ||
| kind: BasicParseErrorKind::EndOfInput, | ||
| .. | ||
| }) => Ok(calculate_contrast_color(base_luminance, Vec::new())), | ||
|
|
||
| Err(e) => Err(e.into()), | ||
| } | ||
| } | ||
|
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| fn parse_color_mix<'i, 't>(input: &mut Parser<'i, 't>) -> Result<CssColor, ParseError<'i, ParserError<'i>>> { | ||
| input.expect_ident_matching("in")?; | ||
| let method = ColorSpaceName::parse(input)?; | ||
|
|
@@ -3233,6 +3350,19 @@ impl CssColor { | |
| } | ||
| } | ||
|
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| /// Returns the [relative luminance](https://www.w3.org/TR/WCAG21/#dfn-relative-luminance) of the color, if it can be calculated. | ||
| fn relative_luminance(&self) -> Option<f32> { | ||
| match self { | ||
| CssColor::CurrentColor => None, | ||
| CssColor::RGBA(rgba) => Some(rgba.relative_luminance()), | ||
| CssColor::LAB(lab) => Some(RGBA::from(**lab).relative_luminance()), | ||
| CssColor::Predefined(pre) => Some(RGBA::from(**pre).relative_luminance()), | ||
| CssColor::Float(float) => Some(RGBA::from(**float).relative_luminance()), | ||
| CssColor::LightDark(..) => None, | ||
| CssColor::System(_) => None, | ||
| } | ||
| } | ||
|
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| /// Mixes this color with another color, including the specified amount of each. | ||
| /// Implemented according to the [`color-mix()`](https://www.w3.org/TR/css-color-5/#color-mix) function. | ||
| pub fn interpolate<T>( | ||
|
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Rather than a cargo flag, we should use the
draftsoption for this. Then at runtime you could decide, and we can expose this to the JS API. We could accept the spec-level as the value. For example: