Avoid poor choices for point colors.

Also adjusts the point size to account for the fact that it now has a border.

common/gal/color4d.cpp

@@ -503,6 +503,14 @@ const COLOR4D COLOR4D::BLACK( 0, 0, 0, 1 );
 const COLOR4D COLOR4D::CLEAR( 1, 0, 1, 0 );
 
 
+int COLOR4D::Distance( const COLOR4D& other ) const
+{
+    return ( r - other.r ) * ( r - other.r )
+            + ( g - other.g ) * ( g - other.g )
+            + ( b - other.b ) * ( b - other.b );
+}
+
+
 EDA_COLOR_T COLOR4D::FindNearestLegacyColor( int aR, int aG, int aB )
 {
     EDA_COLOR_T candidate = EDA_COLOR_T::BLACK;

common/tool/edit_points.cpp

@@ -247,9 +247,24 @@ void EDIT_POINTS::ViewDraw( int aLayer, KIGFX::VIEW* aView ) const
     auto gal = aView->GetGAL();
 
     KIGFX::RENDER_SETTINGS* settings = aView->GetPainter()->GetSettings();
+    KIGFX::COLOR4D          drawColor = settings->GetLayerColor( LAYER_AUX_ITEMS );
+
+    // Don't assume LAYER_AUX_ITEMS is always a good choice.  Compare with background.
+    if( aView->GetGAL()->GetClearColor().Distance( drawColor ) < 0.5 )
+        drawColor.Invert();
+
+    // Linear darkening doesn't fit well with human color perception, and there's no guarantee
+    // that there's enough room for contrast either.
+    KIGFX::COLOR4D bgColor;
+    double         brightness = drawColor.GetBrightness();
+
+    if( brightness > 0.5 )
+        bgColor = drawColor.Darkened( 0.3 ).WithAlpha( 0.8 );
+    else if( brightness > 0.2 )
+        bgColor = drawColor.Darkened( 0.6 ).WithAlpha( 0.8 );
+    else
+        bgColor = drawColor.Brightened( 0.3 ).WithAlpha( 0.8 );
 
-    KIGFX::COLOR4D drawColor      = settings->GetLayerColor( LAYER_AUX_ITEMS );
-    KIGFX::COLOR4D bgColor        = drawColor.Darkened( 0.3 ).WithAlpha( 0.8 );
     KIGFX::COLOR4D highlightColor = settings->GetLayerColor( LAYER_SELECT_OVERLAY );
 
     gal->SetFillColor( drawColor );

include/gal/color4d.h

@@ -357,6 +357,11 @@ public:
      */
     void FromHSV( double aInH, double aInS, double aInV );
 
+    /**
+     * Returns the distance (in RGB space) between two colors.
+     */
+    int Distance( const COLOR4D& other ) const;
+
     /**
      * Returns a legacy color ID that is closest to the given 8-bit RGB values.
      */

include/tool/edit_points.h

@@ -183,7 +183,7 @@ public:
     }
 
     ///< Single point size in pixels
-    static const int POINT_SIZE = 10;
+    static const int POINT_SIZE = 8;
 
     ///< Border size when not hovering
     static const int BORDER_SIZE = 2;