[JENKINS-22686] Don't use fixed pixel count for label distance.

Instead, use a distance of 0.5x the width/height of the label.

This improves appearance in combination with JENKINS-22688 for
different font sizes.

core/src/main/java/hudson/util/NoOverlapCategoryAxis.java

@@ -46,12 +46,6 @@ import java.util.*;
  * @author Kohsuke Kawaguchi
  */
 public class NoOverlapCategoryAxis extends CategoryAxis {
-
-    /**
-     * Minimum distance between labels.
-     */
-    private static final double MIN_DISTANCE = 6.0;
-
     public NoOverlapCategoryAxis(String label) {
         super(label);
     }
@@ -147,10 +141,10 @@ public class NoOverlapCategoryAxis extends CategoryAxis {
                     }
                     r = bounds.getBounds2D();
                     // add margins in all directions
-                    r.add(r.getMaxX() + MIN_DISTANCE, r.getCenterY());
-                    r.add(r.getMinX() - MIN_DISTANCE, r.getCenterY());
-                    r.add(r.getCenterX(), r.getMinY() - MIN_DISTANCE);
-                    r.add(r.getCenterX(), r.getMaxX() + MIN_DISTANCE);
+                    r.add(r.getMaxX() + r.getWidth()/2, r.getCenterY());
+                    r.add(r.getMinX() - r.getWidth()/2, r.getCenterY());
+                    r.add(r.getCenterX(), r.getMinY() - r.getHeight()/2);
+                    r.add(r.getCenterX(), r.getMaxX() + r.getHeight()/2);
                 }
 
                 categoryIndex++;