diff options
Diffstat (limited to 'colors.c')
| -rw-r--r-- | colors.c | 30 |
1 files changed, 30 insertions, 0 deletions
@@ -169,3 +169,33 @@ u32 color_apply_opacity(u32 color, float opacity) { opacity = clampf(opacity, 0.0f, 1.0f); return (color & 0xffffff00) | (u32)((color & 0xff) * opacity); } + + +static float color_relative_luminance(const float rgb[3]) { + // see https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef + float c[3]; + for (int i = 0; i < 3; ++i) { + const float x = rgb[i]; + c[i] = x <= 0.03928f ? x * (1.0f / 12.92f) : powf((x + 0.055f) * (1.0f / 1.055f), 2.4f); + } + return 0.2126f * c[0] + 0.7152f * c[1] + 0.0722f * c[2]; +} + +float color_contrast_ratio(const float rgb1[3], const float rgb2[3]) { + // see https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef + float l1 = color_relative_luminance(rgb1); + float l2 = color_relative_luminance(rgb2); + if (l1 < l2) { + float temp = l1; + l1 = l2; + l2 = temp; + } + return (l1 + 0.05f) / (l2 + 0.05f); +} + +float color_contrast_ratio_u32(u32 color1, u32 color2) { + float rgb1[4], rgb2[4]; + rgba_u32_to_floats(color1, rgb1); + rgba_u32_to_floats(color2, rgb2); + return color_contrast_ratio(rgb1, rgb2); +} |