keep track of when the state of a kate overlay changes, so one may

 decide not to render it again when it is not necessary

src/com/fluendo/jtiger/Item.java

@@ -40,6 +40,8 @@ public class Item {
   private float region_w;
   private float region_h;
 
+  private boolean dirty = true;
+
   /**
    * Create a new item from a Kate event.
    */
@@ -55,6 +57,8 @@ public class Item {
         text = null;
       }
     }
+
+    dirty = false; /* not dirty yet, inactive */
   }
 
   /**
@@ -81,6 +85,8 @@ public class Item {
 
     width = img_width;
     height = img_height;
+
+    dirty = true;
   }
 
   /**
@@ -90,13 +96,18 @@ public class Item {
   public boolean update(Component c, Image img, double t) {
     com.fluendo.jkate.Event ev = kin.ev;
     if (ev == null) return false;
-    if (t >= ev.end_time) return false;
 
-    if (t < ev.start_time) {
+    /* early out if we're not within the lifetime of the event */
+    if (t < ev.start_time) return true;
+    if (t >= ev.end_time) {
       alive = false;
+      dirty = true;
+      return false; /* we're done, and will get destroyed */
     }
-    else {
+
+    if (!alive) {
       alive = true;
+      dirty = true;
     }
 
     Dimension d = new Dimension(img.getWidth(null), img.getHeight(null));
@@ -134,6 +145,8 @@ public class Item {
     setupRegion(c, img);
     renderBackground(c, img);
     renderText(img);
+
+    dirty = false;
   }
 
   /**
@@ -209,4 +222,8 @@ public class Item {
 
     g.dispose();
   }
+
+  public boolean isDirty() {
+    return dirty;
+  }
 }

src/com/fluendo/jtiger/Renderer.java

@@ -25,12 +25,14 @@ import java.awt.*;
 
 public class Renderer {
   private Vector items = new Vector();
+  private boolean dirty = true;
 
   /**
    * Add a new event to the renderer.
    */
   public void add(com.fluendo.jkate.Event ev) {
     items.addElement(new Item(ev));
+    dirty = true;
   }
 
   /**
@@ -42,8 +44,14 @@ public class Renderer {
       boolean ret = ((Item)items.elementAt(n)).update(c, img, t);
       if (!ret) {
         items.removeElementAt(n);
+        dirty = true;
         --n;
       }
+      else {
+        if (((Item)items.elementAt(n)).isDirty()) {
+          dirty = true;
+        }
+      }
     }
     if (items.size() == 0)
       return 1;
@@ -65,6 +73,12 @@ public class Renderer {
       ((Item)items.elementAt(n)).render(c, img);
     }
 
+    dirty = false;
+
     return img;
   }
+
+  public boolean isDirty() {
+    return dirty;
+  }
 }