fix a pixelDensity() issue w/ default display

core/src/processing/awt/ShimAWT.java

@@ -129,16 +129,34 @@ public class ShimAWT implements PConstants {
 
 
   private int displayDensityImpl(int display) {
-    if (display > 0 && display <= displayDevices.length) {
-      GraphicsConfiguration graphicsConfig =
-        displayDevices[display - 1].getDefaultConfiguration();
+    GraphicsConfiguration graphicsConfig = null;
+
+    if (display == -1) {  // the default display
+      GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
+      graphicsConfig = ge.getDefaultScreenDevice().getDefaultConfiguration();
+
+    } else if (display == SPAN) {
+      // walk through all displays, go with lowest common denominator
+      for (int i = 0; i < displayDevices.length; i++) {
+        if (displayDensityImpl(i) == 1) {
+          return 1;
+        }
+      }
+      return 2;  // everyone is density 2
+
+    } else if (display <= displayDevices.length) {
+      graphicsConfig = displayDevices[display - 1].getDefaultConfiguration();
+    }
+
+    if (graphicsConfig == null) {
+      System.err.println("Display " + display + " does not exist, " +
+        "returning 1 for displayDensity(" + display + ")");
+      return 1;  // not the end of the world, so don't throw a RuntimeException
+
+    } else {
       AffineTransform tx = graphicsConfig.getDefaultTransform();
       return (int) Math.round(tx.getScaleX());
     }
-
-    System.err.println("Display " + display + " does not exist, " +
-                       "returning 1 for displayDensity(" + display + ")");
-    return 1;  // not the end of the world, so don't throw a RuntimeException
   }
 
 

core/todo.txt

@@ -3,8 +3,16 @@ X Updating PApplet to use Java 17 (switch statements, etc)
 X XxxList bug with random() if there are zero elements in the array
 X   now throws ArrayIndexOutOfBoundsException
 X   kinda want to return null, but later getting an NPE is more confusing
+X can't do pixelDensity 2 with fullScreen and Java2D
+X   when using fullScreen(), shows error:
+X   "Display -1 does not exist, returning 1 for displayDensity(-1)"
+X   maybe https://github.com/processing/processing4/issues/487
 
 
+_ need alphabetical ordering for json serialization
+_ use choice() instead of random() for list classes
+_ add choice() as a PApplet method for int values of random()?
+
 _ concurrent StringDict et al
 _   why no concurrent TreemMap? https://stackoverflow.com/a/17656453
 _   https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListMap.html