13871 - Show layers in hidden pieces (to owner) correctly. (#13872)

* Add Beanshell performance health warning to Text Label trait (#13737)

* Add performance health warning. Remove Beanshell preference advice as it is not relevant here, except specifically the bit on leading zeros. Generic advice on Beanshell vs Legacy is given in the general section on expressions.

* Slight text mod.

(cherry picked from commit 044cf1e)

* 13871 - Show layers in hidden pieces (to owner) correctly.

---------

Co-authored-by: Mark Benson <[email protected]>
Co-authored-by: Brent <[email protected]>

vassal-app/src/main/java/VASSAL/counters/Hideable.java

@@ -31,6 +31,7 @@
 import VASSAL.i18n.TranslatablePiece;
 import VASSAL.tools.NamedKeyStroke;
 import VASSAL.tools.SequenceEncoder;
+import VASSAL.tools.image.ImageUtils;
 
 import javax.swing.KeyStroke;
 import java.awt.AlphaComposite;
@@ -42,6 +43,7 @@
 import java.awt.Rectangle;
 import java.awt.Shape;
 import java.awt.geom.AffineTransform;
+import java.awt.image.BufferedImage;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -66,6 +68,11 @@ public class Hideable extends Decorator implements TranslatablePiece {
   protected KeyCommand hideCommand;
   protected String description = "";
 
+  // Cache the Hidden image that is shown to the owner. Only re-generate when Zoom or piece state changes.
+  protected BufferedImage cachedImage;
+  protected double cachedZoom = -1d;
+  protected String cachedState = "";
+
   @Override
   public void setProperty(Object key, Object val) {
     if (HIDDEN_BY.equals(key)) {
@@ -210,14 +217,48 @@ public void draw(Graphics g, int x, int y, Component obs, double zoom) {
         g2d.fill(t.createTransformedShape(piece.getShape()));
       }
 
-      final Composite oldComposite = g2d.getComposite();
-      g2d.setComposite(
-        AlphaComposite.getInstance(AlphaComposite.SRC_OVER, transparency)
-      );
-      piece.draw(g, x, y, obs, zoom);
-      g2d.setComposite(oldComposite);
+      // Determine piece bounds at current zoom
+      final Rectangle bounds = piece.getShape().getBounds();
+      final int w = (int) Math.ceil(bounds.width * zoom);
+      final int h = (int) Math.ceil(bounds.height * zoom);
+
+      // If there's nothing visible at this zoom, skip
+      if (w <= 0 || h <= 0) {
+        return;
+      }
+
+      final String visibleState = (String) piece.getProperty(Properties.VISIBLE_STATE);
+      if (cachedImage == null || zoom != cachedZoom || ! cachedState.equals(visibleState)) {
+
+        // Create an in-memory cached image and draw piece fully opaque
+        cachedImage = ImageUtils.createCompatibleTranslucentImage(w, h);
+        cachedZoom = zoom;
+        cachedState = visibleState;
+
+        final Graphics2D cg = cachedImage.createGraphics();
+        try {
+          cg.scale(zoom, zoom);
+          cg.translate(-bounds.x, -bounds.y);
+
+          piece.draw(cg, 0, 0, obs, 1.0); // Fully opaque
+        }
+        finally {
+          cg.dispose();
+        }
+      }
+
+      // Apply the appropriate transparency to the overall image
+      final Composite oldComp = g2d.getComposite();
+      g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, transparency));
+
+      final int drawX = x + (int) Math.round(bounds.x * zoom);
+      final int drawY = y + (int) Math.round(bounds.y * zoom);
+      g2d.drawImage(cachedImage, drawX, drawY, obs);
+
+      g2d.setComposite(oldComp);
     }
     else {
+      // Normal draw at the end
       piece.draw(g, x, y, obs, zoom);
     }
   }
@@ -419,4 +460,4 @@ public List<NamedKeyStroke> getNamedKeyStrokeList() {
   public List<String> getMenuTextList() {
     return List.of(command);
   }
-}
+}