Do background contrast fallback at runtime

When a theme doesn't supply background contrast values, we take an educated guess based on whether it's a dark or light theme.
We didn't update the values when switching only color schemes at runtime (when theme follows it).
This lead to washed out Plasma popup and panel backgrounds. Instead, compute the fallback value at runtime.
Also, while at it, update complimentary colorscheme as well, which was forgotten here.

BUG: 401142

Differential Revision: https://phabricator.kde.org/D18487

src/plasma/private/theme_p.cpp

@@ -71,9 +71,9 @@ ThemePrivate::ThemePrivate(QObject *parent)
       useGlobal(true),
       hasWallpapers(false),
       fixedName(false),
-      backgroundContrast(0),
+      backgroundContrast(qQNaN()),
-      backgroundIntensity(0),
+      backgroundIntensity(qQNaN()),
-      backgroundSaturation(0),
+      backgroundSaturation(qQNaN()),
       backgroundContrastEnabled(true),
       apiMajor(1),
       apiMinor(0),
@@ -728,23 +728,9 @@ void ThemePrivate::processContrastSettings(KConfigBase *metadata)
         cg = KConfigGroup(metadata, "ContrastEffect");
         backgroundContrastEnabled = cg.readEntry("enabled", false);
 
-        //if (backgroundContrastEnabled) {
+        backgroundContrast = cg.readEntry("contrast", qQNaN());
-        // Make up sensible default values, based on the background color
+        backgroundIntensity = cg.readEntry("intensity", qQNaN());
-        // This works for a light theme -- lighting up the background
+        backgroundSaturation = cg.readEntry("saturation", qQNaN());
-        qreal _contrast = 0.3;
-        qreal _intensity = 1.9;
-        qreal _saturation = 1.7;
-
-        // If we're using a dark background color, darken the background
-        if (qGray(color(Plasma::Theme::BackgroundColor).rgb()) < 127) {
-            _contrast = 0.45;
-            _intensity = 0.45;
-            _saturation = 1.7;
-        }
-        backgroundContrast = cg.readEntry("contrast", _contrast);
-        backgroundIntensity = cg.readEntry("intensity", _intensity);
-        backgroundSaturation = cg.readEntry("saturation", _saturation);
-        //}
     } else {
         backgroundContrastEnabled = false;
     }

src/plasma/theme.cpp

@@ -477,16 +477,36 @@ bool Theme::backgroundContrastEnabled() const
 
 qreal Theme::backgroundContrast() const
 {
+    if (qIsNaN(d->backgroundContrast)) {
+        // Make up sensible default values, based on the background color
+        // If we're using a dark background color, darken the background
+        if (qGray(color(Plasma::Theme::BackgroundColor).rgb()) < 127) {
+            return 0.45;
+        // for a light theme lighten up the background
+        } else {
+            return 0.3;
+        }
+    }
     return d->backgroundContrast;
 }
 
 qreal Theme::backgroundIntensity() const
 {
+    if (qIsNaN(d->backgroundIntensity)) {
+        if (qGray(color(Plasma::Theme::BackgroundColor).rgb()) < 127) {
+            return 0.45;
+        } else {
+            return 1.9;
+        }
+    }
     return d->backgroundIntensity;
 }
 
 qreal Theme::backgroundSaturation() const
 {
+    if (qIsNaN(d->backgroundSaturation)) {
+        return 1.7;
+    }
     return d->backgroundSaturation;
 }