track/serato/tags: Add conversion functions for Serato's track colors

src/track/serato/tags.cpp

@@ -2,6 +2,64 @@
 
 namespace mixxx {
 
+RgbColor::optional_t SeratoTags::colorFromStoredTrackColor(RgbColor color) {
+    // Serato stores Track colors differently from how they are displayed in
+    // the library column. Instead of the color from the library view, the
+    // value from the color picker is stored instead (which is different).
+    // To make sure that the track looks the same in both Mixxx' and Serato's
+    // libraries, we need to convert between the two values.
+    //
+    // See this for details:
+    // https://github.com/Holzhaus/serato-tags/blob/master/docs/colors.md#track-colors
+
+    quint32 value = static_cast<quint32>(color);
+
+    if (color == 0xFFFFFF) {
+        return RgbColor::nullopt();
+    }
+
+    if (color == 0x999999) {
+        return RgbColor::optional(0x090909);
+    }
+
+    if (color == 0x000000) {
+        return RgbColor::optional(0x333333);
+    }
+
+    value = (value < 0x666666) ? value + 0x99999A : value - 0x666666;
+    return RgbColor::optional(value);
+}
+
+RgbColor SeratoTags::colorToStoredTrackColor(RgbColor::optional_t color) {
+    if (!color) {
+        return RgbColor(0xFFFFFF);
+    }
+
+    quint32 value = static_cast<quint32>(*color);
+
+    if (value == 0x090909) {
+        return RgbColor(0x999999);
+    }
+
+    if (value == 0x333333) {
+        return RgbColor(0x000000);
+    }
+
+    // Special case: 0x999999 and 0x99999a are not representable as Serato
+    // track color We'll just modify them a little, so that the look the
+    // same in Serato.
+    if (value == 0x999999) {
+        return RgbColor(0x999998);
+    }
+
+    if (value == 0x99999a) {
+        return RgbColor(0x99999b);
+    }
+
+    value = (value < 0x99999A) ? value + 0x666666 : value - 0x99999A;
+    return RgbColor(value);
+}
+
 RgbColor::optional_t SeratoTags::getTrackColor() const {
     RgbColor::optional_t color = m_seratoMarkers.getTrackColor();
 
@@ -10,6 +68,10 @@ RgbColor::optional_t SeratoTags::getTrackColor() const {
         color = m_seratoMarkers2.getTrackColor();
     }
 
+    if (color) {
+        color = SeratoTags::colorFromStoredTrackColor(*color);
+    }
+
     return color;
 }
 

src/track/serato/tags.h

@@ -15,6 +15,9 @@ class SeratoTags final {
 
     SeratoTags() = default;
 
+    static RgbColor colorToStoredTrackColor(RgbColor::optional_t color);
+    static RgbColor::optional_t colorFromStoredTrackColor(RgbColor color);
+
     bool isEmpty() const {
         return m_seratoMarkers.isEmpty() && m_seratoMarkers2.isEmpty();
     }