ttools: use static instances for plot modes

Plot Modes as used in various plot types are now taken from static
members of the ShapeMode class rather than a new (stateless) instance
each time, which is a bit tidier and makes it easier to distinguish
whether two modes (hence Plotters) are the same.

ttools/src/main/uk/ac/starlink/ttools/plot2/geom/SphereDataGeom.java

@@ -24,7 +24,7 @@ public class SphereDataGeom implements DataGeom {
     /**
      * Private singleton constructor.
      */
-    public SphereDataGeom() {
+    private SphereDataGeom() {
     }
 
     /**

ttools/src/main/uk/ac/starlink/ttools/plot2/geom/TimePlotType.java

@@ -48,8 +48,8 @@ public Plotter[] getPlotters() {
                                 false, StyleKeys.ERROR_SHAPE_1D );
         return new Plotter[] {
             new LinePlotter(),
-            ShapePlotter.createFlatPlotter( MarkForm.SINGLE ),
-            ShapePlotter.createFlatPlotter( errorForm ),
+            ShapePlotter.createFlat2dPlotter( MarkForm.SINGLE ),
+            ShapePlotter.createFlat2dPlotter( errorForm ),
             new SpectrogramPlotter( TimeDataGeom.T_COORD ),
             new LabelPlotter(),
             FunctionPlotter.PLANE,

ttools/src/main/uk/ac/starlink/ttools/plot2/layer/ShapeMode.java

@@ -54,6 +54,7 @@
  * @since    19 Feb 2013
  */
 public abstract class ShapeMode implements ModePlotter.Mode {
+
     private final String name_;
     private final Icon icon_;
     private final Coord[] extraCoords_;
@@ -70,34 +71,50 @@ public abstract class ShapeMode implements ModePlotter.Mode {
      */
     private static final int NO_BINS = Integer.MAX_VALUE;
 
-    /**
-     * List of modes suitable for use with 2D plotting.
-     */
+    /** Auto density mode, no user settings. */
+    public static final ShapeMode AUTO = new AutoDensityMode();
+
+    /** Simple flat mode for use with 2D plots.  */
+    public static final ShapeMode FLAT2D = new FlatMode( false, BIN_THRESH_2D );
+
+    /** Simple flat mode for use with 3D plots. */
+    public static final ShapeMode FLAT3D = new FlatMode( false, NO_BINS );
+
+    /** Transparency with automatic adjustment of opacity level. */
+    public static final ShapeMode TRANSLUCENT = new AutoTransparentMode();
+
+    /** Transparency with explicit opacity setting, suitable for 2D plots. */
+    public static final ShapeMode TRANSPARENT2D = new FlatMode( true,
+                                                                BIN_THRESH_2D );
+
+    /** Transparency with explicit opacity setting, suitable for 3D plots. */
+    public static final ShapeMode TRANSPARENT3D = new FlatMode( true, NO_BINS );
+
+    /** Configurable density mode. */
+    public static final ShapeMode DENSITY = new CustomDensityMode();
+
+    /** Aux variable colouring mode. */
+    public static final ShapeMode AUX = new AuxShadingMode( true );
+
+    /** List of modes suitable for use with 2D plotting. */
     public static final ShapeMode[] MODES_2D = new ShapeMode[] {
-        new AutoDensityMode(),
-        new FlatMode( false, BIN_THRESH_2D ),
-        new AutoTransparentMode(),
-        new FlatMode( true, BIN_THRESH_2D ),
-        new CustomDensityMode(),
-        new AuxShadingMode( true ),
+        AUTO,
+        FLAT2D,
+        TRANSLUCENT,
+        TRANSPARENT2D,
+        DENSITY,
+        AUX,
     };
 
-    /**
-     * List of modes suitable for use with 3D plotting.
-     */
+    /** List of modes suitable for use with 3D plotting. */
     public static final ShapeMode[] MODES_3D = new ShapeMode[] {
-        new FlatMode( false, NO_BINS ),
-        new AutoTransparentMode(),
-        new FlatMode( true, NO_BINS ),
-        new CustomDensityMode(),
-        new AuxShadingMode( true ),
+        FLAT3D,
+        TRANSLUCENT,
+        TRANSPARENT3D,
+        DENSITY,
+        AUX,
     };
 
-    /**
-     * Simple flat mode.
-     */
-    public static final ShapeMode FLAT = new FlatMode( false, NO_BINS );
-
     /**
      * Constructor.
      *

ttools/src/main/uk/ac/starlink/ttools/plot2/layer/ShapePlotter.java

@@ -111,14 +111,16 @@ public static ShapeModePlotter[] createShapePlotters( ShapeForm[] forms,
     }
 
     /**
-     * Creates a single ShapePlotter using mode flat.
-     * It is not intended for use with other plotters of the same form.
+     * Creates a single ShapePlotter using mode flat.  Suitable for
+     * 2d plot types only.
+     * The returned object is not a {@link ModePlotter}, so will not be
+     * ganged together with other ShapePlotters.
      *
      * @param   form   shape form
-     * @return   new plotter
+     * @return   new 2d plotter
      */
-    public static ShapePlotter createFlatPlotter( ShapeForm form ) {
-        return new ShapePlotter( form.getFormName(), form, ShapeMode.FLAT );
+    public static ShapePlotter createFlat2dPlotter( ShapeForm form ) {
+        return new ShapePlotter( form.getFormName(), form, ShapeMode.FLAT2D );
     }
 
     /**