Added MisoUtil.getTileHash(), made both SceneBlock and AutoFringer use

it to pick random tiles based on x/y location.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@2622 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/miso/client/SceneBlock.java

@@ -1,5 +1,5 @@
 //
-// $Id: SceneBlock.java,v 1.16 2003/05/23 19:35:11 mdb Exp $
+// $Id: SceneBlock.java,v 1.17 2003/05/29 01:58:06 ray Exp $
 
 package com.threerings.miso.client;
 
@@ -206,10 +206,8 @@ public class SceneBlock
     {
         BaseTile tile = _base[index(tx, ty)];
         if (tile == null && _defset != null) {
-            long seed = ((tx^ty) ^ multiplier) & mask;
-            long hash = (seed * multiplier + addend) & mask;
-            int tidx = (int)((hash >> 10) % _defset.getTileCount());
-            tile = (BaseTile)_defset.getTile(tidx);
+            tile = (BaseTile)_defset.getTile(
+                MisoUtil.getTileHash(tx, ty) % _defset.getTileCount());
         }
         return tile;
     }

src/java/com/threerings/miso/tile/AutoFringer.java

@@ -1,5 +1,5 @@
 //
-// $Id: AutoFringer.java,v 1.23 2003/05/29 01:04:58 ray Exp $
+// $Id: AutoFringer.java,v 1.24 2003/05/29 01:58:06 ray Exp $
 
 package com.threerings.miso.tile;
 
@@ -33,6 +33,7 @@ import com.threerings.media.image.ImageManager;
 import com.threerings.media.image.Mirage;
 
 import com.threerings.miso.data.MisoSceneModel;
+import com.threerings.miso.util.MisoUtil;
 
 /**
  * Automatically fringes a scene according to the rules in the supplied
@@ -110,16 +111,7 @@ public class AutoFringer
             }
         }
 
-        return composeFringeTile(frecs, masks, generateHashValue(col, row));
-    }
-
-    /**
-     * Create a hash value for picking which fringe to use for a particular
-     * tile.
-     */
-    protected int generateHashValue (int col, int row)
-    {
-        return col ^ row;
+        return composeFringeTile(frecs, masks, MisoUtil.getTileHash(col, row));
     }
 
     /**

src/java/com/threerings/miso/tile/FringeConfiguration.java

@@ -1,5 +1,5 @@
 //
-// $Id: FringeConfiguration.java,v 1.14 2003/05/29 01:04:58 ray Exp $
+// $Id: FringeConfiguration.java,v 1.15 2003/05/29 01:58:06 ray Exp $
 
 package com.threerings.miso.tile;
 
@@ -122,10 +122,8 @@ public class FringeConfiguration implements Serializable
     public FringeTileSetRecord getFringe (int baseset, int hashValue)
     {
         FringeRecord f = (FringeRecord) _frecs.get(baseset);
-
-        int size = f.tilesets.size();
-        int pick = Math.abs(hashValue) % size;
-        return (FringeTileSetRecord) f.tilesets.get(pick);
+        return (FringeTileSetRecord) f.tilesets.get(
+            hashValue % f.tilesets.size());
     }
 
     /** The mapping from base tileset id to fringerecord. */

src/java/com/threerings/miso/util/MisoUtil.java

@@ -1,5 +1,5 @@
 //
-// $Id: MisoUtil.java,v 1.21 2003/04/19 22:40:34 mdb Exp $
+// $Id: MisoUtil.java,v 1.22 2003/05/29 01:58:06 ray Exp $
 
 package com.threerings.miso.util;
 
@@ -156,6 +156,19 @@ public class MisoUtil
         return dir;
     }
 
+    /**
+     * Compute some hash value for "randomizing" tileset picks
+     * based on x and y coordinates.
+     *
+     * @return a positive, seemingly random number based on x and y.
+     */
+    public static int getTileHash (int x, int y)
+    {
+        long seed = ((x ^ y) ^ MULTIPLIER) & MASK;
+        long hash = (seed * MULTIPLIER + ADDEND) & MASK;
+        return (int) (hash >>> 30);
+    }
+
     /**
      * Returns the tile coordinate of the given full coordinate.
      */
@@ -503,4 +516,8 @@ public class MisoUtil
 
     /** Multiplication factor to embed tile coords in full coords. */
     protected static final int FULL_TILE_FACTOR = 100;
+
+    protected static final long MULTIPLIER = 0x5DEECE66DL;
+    protected static final long ADDEND = 0xBL;
+    protected static final long MASK = (1L << 48) - 1;
 }