Added mechanism by which the sprite manager can be informed that the view

on which its sprites are rendered was scrolled so that it can generate the
appropriate dirty rectangles or update its sprite's positions.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@1045 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/media/sprite/SpriteManager.java

@@ -1,5 +1,5 @@
 //
-// $Id: SpriteManager.java,v 1.23 2002/02/19 07:41:36 mdb Exp $
+// $Id: SpriteManager.java,v 1.24 2002/02/19 19:55:14 mdb Exp $
 
 package com.threerings.media.sprite;
 
@@ -50,6 +50,40 @@ public class SpriteManager
         _ty = ty;
     }
 
+    /**
+     * Lets the sprite manager know that the view is about to scroll by
+     * the specified offsets. It can update the positions of its sprites
+     * if they are tracking the scrolled view, or generate dirty regions
+     * for the sprites that remain in place (meaning they move relative to
+     * the scrolling view). Regions invalidated by the scrolled sprites
+     * should be appended to the supplied invalid rectangles list.
+     */
+    public void viewWillScroll (int dx, int dy, List invalidRects)
+    {
+        // presently all sprites move relative to the scrolling view
+        int size = _sprites.size();
+        for (int i = 0; i < size; i++) {
+            Sprite sprite = (Sprite)_sprites.get(i);
+            Rectangle dirty = new Rectangle(sprite.getBounds());
+
+            // expand the rectangle to contain the scrolled regions
+            int ex = dirty.x - dx, ey = dirty.y - dy;
+            if (dx < 0) {
+                ex += dirty.width;
+            }
+            if (dy < 0) {
+                ey += dirty.height;
+            }
+            dirty.add(ex, ey);
+
+            // translate the rectangle according to our viewport offset
+            dirty.translate(-_tx, -_ty);
+
+            // append it to the list
+            invalidRects.add(dirty);
+        }
+    }
+
     /**
      * Add a rectangle to the dirty rectangle list.
      *