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fix(sensors): keep text contrast against the real background #5

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228 changes: 228 additions & 0 deletions sensors/contrast.vala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,228 @@
namespace SensorsContrast {
public const double TARGET_PREFERRED = 7.0;
public const double TARGET_MINIMUM = 4.5;

public struct Color {
public double r;
public double g;
public double b;
public double a;

public Color(double r, double g, double b, double a = 1.0) {
this.r = r;
this.g = g;
this.b = b;
this.a = a;
}

public string to_hex() {
return "#%02x%02x%02x".printf(to_byte(r), to_byte(g), to_byte(b));
}
}

private uint to_byte(double v) {
return (uint) Math.round(v.clamp(0.0, 1.0) * 255.0);
}

private double linearize(double c) {
return c <= 0.04045 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
}

public double relative_luminance(Color c) {
return 0.2126 * linearize(c.r) + 0.7152 * linearize(c.g) + 0.0722 * linearize(c.b);
}

public double contrast_ratio(Color a, Color b) {
double la = relative_luminance(a);
double lb = relative_luminance(b);
double hi = double.max(la, lb);
double lo = double.min(la, lb);
return (hi + 0.05) / (lo + 0.05);
}

public Color composite(Color fg, Color under) {
double a = fg.a.clamp(0.0, 1.0);
return Color(fg.r * a + under.r * (1.0 - a),
fg.g * a + under.g * (1.0 - a),
fg.b * a + under.b * (1.0 - a), 1.0);
}

public Color mix(Color from, Color to, double t) {
return Color(from.r + (to.r - from.r) * t,
from.g + (to.g - from.g) * t,
from.b + (to.b - from.b) * t, 1.0);
}

public Color near_black() {
return Color(0.08, 0.08, 0.08);
}

public Color near_white() {
return Color(0.96, 0.96, 0.96);
}

public Color scrim_for(Color theme_bg) {
bool dark = relative_luminance(theme_bg) < 0.4;
return dark ? Color(0.09, 0.09, 0.10) : Color(0.96, 0.96, 0.97);
}

public Color neutral_for(Color bg) {
Color dark = near_black();
Color light = near_white();
Color best = contrast_ratio(dark, bg) >= contrast_ratio(light, bg) ? dark : light;
if (contrast_ratio(best, bg) >= TARGET_PREFERRED) {
return best;
}
Color black = Color(0.0, 0.0, 0.0);
Color white = Color(1.0, 1.0, 1.0);
return contrast_ratio(black, bg) >= contrast_ratio(white, bg) ? black : white;
}

private void to_hsl(Color c, out double h, out double s, out double l) {
double mx = double.max(c.r, double.max(c.g, c.b));
double mn = double.min(c.r, double.min(c.g, c.b));
double d = mx - mn;
l = (mx + mn) / 2.0;
h = 0.0;
s = 0.0;
if (d < 1e-9) {
return;
}
s = d / (1.0 - Math.fabs(2.0 * l - 1.0));
if (mx == c.r) {
h = ((c.g - c.b) / d) % 6.0;
} else if (mx == c.g) {
h = (c.b - c.r) / d + 2.0;
} else {
h = (c.r - c.g) / d + 4.0;
}
h = h * 60.0;
if (h < 0.0) {
h += 360.0;
}
}

private Color from_hsl(double h, double s, double l) {
double c = (1.0 - Math.fabs(2.0 * l - 1.0)) * s;
double x = c * (1.0 - Math.fabs((h / 60.0) % 2.0 - 1.0));
double m = l - c / 2.0;
double r = 0.0, g = 0.0, b = 0.0;
if (h < 60.0) { r = c; g = x; }
else if (h < 120.0) { r = x; g = c; }
else if (h < 180.0) { g = c; b = x; }
else if (h < 240.0) { g = x; b = c; }
else if (h < 300.0) { r = x; b = c; }
else { r = c; b = x; }
return Color(r + m, g + m, b + m);
}

public Color ensure_contrast(Color fg, Color bg, double target) {
if (contrast_ratio(fg, bg) >= target) {
return Color(fg.r, fg.g, fg.b);
}
double h, s, l;
to_hsl(fg, out h, out s, out l);
double extreme = contrast_ratio(near_black(), bg) >= contrast_ratio(near_white(), bg)
? 0.0 : 1.0;
if (contrast_ratio(from_hsl(h, s, extreme), bg) < target) {
return from_hsl(h, s, extreme);
}
double near = l;
double far = extreme;
for (int i = 0; i < 24; i++) {
double mid = (near + far) / 2.0;
if (contrast_ratio(from_hsl(h, s, mid), bg) >= target) {
far = mid;
} else {
near = mid;
}
}
return from_hsl(h, s, far);
}

public Color best_contrast(Color fg, Color bg) {
Color strong = ensure_contrast(fg, bg, TARGET_PREFERRED);
if (contrast_ratio(strong, bg) >= TARGET_PREFERRED) {
return strong;
}
return ensure_contrast(fg, bg, TARGET_MINIMUM);
}

public Color muted_for(Color neutral, Color bg) {
Color result = neutral;
for (int i = 1; i <= 20; i++) {
Color candidate = mix(neutral, bg, i / 40.0);
if (contrast_ratio(candidate, bg) < 5.0) {
break;
}
result = candidate;
}
return result;
}

public Color fallback_for(string role, bool dark_background) {
switch (role) {
case "error":
return dark_background ? Color(1.0, 0.45, 0.42) : Color(0.70, 0.06, 0.08);
case "warning":
return dark_background ? Color(1.0, 0.72, 0.25) : Color(0.60, 0.33, 0.0);
case "accent":
return dark_background ? Color(0.55, 0.75, 1.0) : Color(0.05, 0.30, 0.72);
default:
return dark_background ? Color(0.45, 0.90, 0.55) : Color(0.05, 0.42, 0.15);
}
}

public Color median_by_luminance(Color[] samples) {
if (samples.length == 0) {
return Color(0.5, 0.5, 0.5);
}
int n = samples.length;
double[] lum = new double[n];
int[] order = new int[n];
for (int i = 0; i < n; i++) {
lum[i] = relative_luminance(samples[i]);
order[i] = i;
}
for (int i = 1; i < n; i++) {
int key = order[i];
int j = i - 1;
while (j >= 0 && lum[order[j]] > lum[key]) {
order[j + 1] = order[j];
j--;
}
order[j + 1] = key;
}
return samples[order[n / 2]];
}

public class Palette : Object {
public Color bg;
public Color neutral;
public Color muted;
public Color ok;
public Color hot;
public Color crit;
public Color accent;

public Palette(Color bg, Color? theme_ok, Color? theme_hot, Color? theme_crit, Color? theme_accent) {
this.bg = bg;
bool dark = relative_luminance(bg) < 0.18;
neutral = neutral_for(bg);
muted = muted_for(neutral, bg);
ok = best_contrast(theme_ok ?? fallback_for("success", dark), bg);
hot = best_contrast(theme_hot ?? fallback_for("warning", dark), bg);
crit = best_contrast(theme_crit ?? fallback_for("error", dark), bg);
accent = best_contrast(theme_accent ?? fallback_for("accent", dark), bg);
}

public bool equals(Palette other) {
return bg.to_hex() == other.bg.to_hex()
&& neutral.to_hex() == other.neutral.to_hex()
&& ok.to_hex() == other.ok.to_hex()
&& hot.to_hex() == other.hot.to_hex()
&& crit.to_hex() == other.crit.to_hex()
&& accent.to_hex() == other.accent.to_hex();
}
}
}
8 changes: 8 additions & 0 deletions sensors/meson.build
View file
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
shared_module('sensors',
'sensors.vala',
'contrast.vala',
dependencies: [dependency('gtk4'), libsingularity_dep, system_dep, dependency('libpeas-2'), meson.get_compiler('c').find_library('m')],
c_args: ['-DGETTEXT_PACKAGE="singularity-desktop"'],
install: true,
Expand All @@ -13,3 +14,10 @@ configure_file(
install: true,
install_dir: get_option('libdir') / 'singularity/plugins/sensors'
)

contrast_test = executable('sensors-contrast-test',
'contrast.vala', 'tests/contrast-test.vala',
dependencies: [dependency('glib-2.0'), dependency('gobject-2.0'), meson.get_compiler('c').find_library('m')],
install: false
)
test('sensors-contrast', contrast_test)
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