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terminal: add w3c luminance formula

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This commit is contained in:
Mitchell Hashimoto
2023-08-30 10:10:45 -07:00
parent 3391908a82
commit 0e8412ec19
1 changed files with 23 additions and 0 deletions
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23
src/terminal/color.zig
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@ -103,6 +103,29 @@ pub const RGB = struct {
return self.r == other.r and self.g == other.g and self.b == other.b;
}
/// Calculates luminance based on the W3C formula. This returns a
/// normalized value between 0 and 1 where 0 is black and 1 is white.
///
/// https://www.w3.org/TR/WCAG20/#relativeluminancedef
pub fn luminance(self: RGB) f64 {
const r_lum = componentLuminance(self.r);
const g_lum = componentLuminance(self.g);
const b_lum = componentLuminance(self.b);
return 0.2126 * r_lum + 0.7152 * g_lum + 0.0722 * b_lum;
}
/// Calculates single-component luminance based on the W3C formula.
///
/// Expects sRGB color space which at the time of writing we don't
/// generally use but it's a good enough approximation until we fix that.
/// https://www.w3.org/TR/WCAG20/#relativeluminancedef
fn componentLuminance(c: u8) f64 {
const c_f64: f64 = @floatFromInt(c);
const normalized: f64 = c_f64 / 255;
if (normalized <= 0.03928) return normalized / 12.92;
return std.math.pow(f64, (normalized + 0.055) / 1.055, 2.4);
}
test "size" {
try std.testing.expectEqual(@as(usize, 24), @bitSizeOf(RGB));
try std.testing.expectEqual(@as(usize, 3), @sizeOf(RGB));