By default, generate new layer colors from a random selection

in a preset palette

The palette is packaged as resources/new_layer_colors.gpl

TODO: allow users to set a different palette

python/core/qgscolorschemeregistry.sip.in

@@ -50,6 +50,13 @@ Adds all default color schemes to this color scheme.
 .. seealso:: :py:func:`addColorScheme`
 
 .. seealso:: :py:func:`addUserSchemes`
+%End
+
+    void initStyleScheme();
+%Docstring
+Initializes the default random style color scheme for the user.
+
+.. versionadded:: 3.2
 %End
 
     void addUserSchemes();

src/core/qgsapplication.cpp

@@ -271,6 +271,9 @@ void QgsApplication::init( QString profileFolder )
   // so we read actual value in main.cpp
   ABISYM( mMaxThreads ) = -1;
 
+  colorSchemeRegistry()->addDefaultSchemes();
+  colorSchemeRegistry()->initStyleScheme();
+
   ABISYM( mInitialized ) = true;
 }
 
@@ -1718,7 +1721,6 @@ QgsApplication::ApplicationMembers::ApplicationMembers()
   mFieldFormatterRegistry = new QgsFieldFormatterRegistry();
   mSvgCache = new QgsSvgCache();
   mColorSchemeRegistry = new QgsColorSchemeRegistry();
-  mColorSchemeRegistry->addDefaultSchemes();
   mPaintEffectRegistry = new QgsPaintEffectRegistry();
   mSymbolLayerRegistry = new QgsSymbolLayerRegistry();
   mRendererRegistry = new QgsRendererRegistry();

src/core/qgscolorschemeregistry.cpp

@@ -51,6 +51,17 @@ void QgsColorSchemeRegistry::addDefaultSchemes()
   addUserSchemes();
 }
 
+void QgsColorSchemeRegistry::initStyleScheme()
+{
+  QString stylePalette = QgsApplication::pkgDataPath() + QStringLiteral( "/resources/new_layer_colors.gpl" );
+  if ( QFileInfo::exists( stylePalette ) )
+  {
+    QgsUserColorScheme *scheme = new QgsUserColorScheme( stylePalette );
+    addColorScheme( scheme );
+    setRandomStyleColorScheme( scheme );
+  }
+}
+
 void QgsColorSchemeRegistry::addUserSchemes()
 {
   QString palettesDir = QgsApplication::qgisSettingsDirPath() + "/palettes";

src/core/qgscolorschemeregistry.h

@@ -58,6 +58,12 @@ class CORE_EXPORT QgsColorSchemeRegistry
      */
     void addDefaultSchemes();
 
+    /**
+     * Initializes the default random style color scheme for the user.
+     * \since QGIS 3.2
+     */
+    void initStyleScheme();
+
     /**
      * Creates schemes for all gpl palettes in the user's palettes folder.
      * \see populateFromInstance

tests/src/core/testqgscolorschemeregistry.cpp

@@ -104,7 +104,8 @@ class TestQgsColorSchemeRegistry : public QObject
 
 void TestQgsColorSchemeRegistry::initTestCase()
 {
-
+  QgsApplication::init();
+  QgsApplication::initQgis();
 }
 
 void TestQgsColorSchemeRegistry::cleanupTestCase()
@@ -249,6 +250,8 @@ void TestQgsColorSchemeRegistry::fetchRandomStyleColor()
     QVERIFY( registry->fetchRandomStyleColor().isValid() );
   }
 
+  // we expect the default application color scheme registry to have a randomStyleColorScheme set
+  QVERIFY( QgsApplication::colorSchemeRegistry()->randomStyleColorScheme() );
 }
 
 QGSTEST_MAIN( TestQgsColorSchemeRegistry )