Regression Curves: Use a contrast color for the regression curves

Use a list of predefined colors, and select the color with the larges RGB difference to the source curve. This will ensure that we avoid ending up with fully white or fully black curves, unable to see.

ApplicationLibCode/Application/Tools/RiaColorTools.cpp

@@ -136,6 +136,30 @@ cvf::Color3f RiaColorTools::fromQColorTo3f( QColor color )
     return cvf::Color3f( color.redF(), color.greenF(), color.blueF() );
 }
 
+//--------------------------------------------------------------------------------------------------
+/// Find the color with larges distance to the given color based on RGB distance
+//--------------------------------------------------------------------------------------------------
+cvf::Color3f RiaColorTools::selectContrastColorFromCandiates( cvf::Color3f color, const cvf::Color3fArray& candidates )
+{
+    if ( candidates.size() == 0 ) return color;
+
+    float        maxDiff       = 0.0f;
+    cvf::Color3f selectedColor = color;
+
+    for ( const auto& candidate : candidates )
+    {
+        const auto diff = std::fabs( color.r() - candidate.r() ) + std::fabs( color.g() - candidate.g() ) +
+                          std::fabs( color.b() - candidate.b() );
+        if ( diff > maxDiff )
+        {
+            maxDiff       = diff;
+            selectedColor = candidate;
+        }
+    }
+
+    return selectedColor;
+}
+
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------

ApplicationLibCode/Application/Tools/RiaColorTools.h

@@ -42,6 +42,8 @@ public:
     static QColor       toQColor( cvf::Color4f color );
     static cvf::Color3f fromQColorTo3f( QColor );
 
+    static cvf::Color3f selectContrastColorFromCandiates( cvf::Color3f color, const cvf::Color3fArray& candidates );
+
     static QColor       textColor();
     static cvf::Color3f textColor3f();