Added //gmask to set a *GLOBAL* mask that affects nearly ALL operations. Now you can confine //sphere to a region or create //walls that do not replace existing blocks.

plugin.yml

@@ -65,6 +65,11 @@ commands:
         description: Modify block change limit
         usage: /<command> <limit>
         permissions: 'worldedit.limit'
+    /gmask:
+        description: Set the global mask
+        usage: /<command> [mask]
+        aliases: ['gmask']
+        permissions: 'worldedit.global-mask'
     /hcyl:
         description: Generate a hollow cylinder
         usage: /<command> <block> <radius> [height] 

src/main/java/com/sk89q/worldedit/EditSession.java

@@ -33,6 +33,7 @@ import com.sk89q.worldedit.regions.*;
 import com.sk89q.worldedit.util.TreeGenerator;
 import com.sk89q.worldedit.bags.*;
 import com.sk89q.worldedit.blocks.*;
+import com.sk89q.worldedit.masks.Mask;
 import com.sk89q.worldedit.patterns.*;
 
 /**
@@ -109,6 +110,11 @@ public class EditSession {
      */
     private Set<Integer> missingBlocks = new HashSet<Integer>();
     
+    /**
+     * Mask to cover operations.
+     */
+    private Mask mask;
+
     /**
      * Construct the object with a maximum number of blocks.
      * 
@@ -162,6 +168,12 @@ public class EditSession {
             return false;
         }
         
+        if (mask != null) {
+            if (!mask.matches(this, pt)) {
+                return false;
+            }
+        }
+        
         int existing = world.getBlockType(pt);
 
         // Clear the container block so that it doesn't drop items
@@ -2245,4 +2257,22 @@ public class EditSession {
     public int getBlockChangeCount() {
         return original.size();
     }
+
+    /**
+     * Get the mask.
+     * 
+     * @return mask, may be null
+     */
+    public Mask getMask() {
+        return mask;
+    }
+
+    /**
+     * Set a mask.
+     * 
+     * @param mask mask or null
+     */
+    public void setMask(Mask mask) {
+        this.mask = mask;
+    }
 }

src/main/java/com/sk89q/worldedit/LocalSession.java

@@ -38,6 +38,7 @@ import com.sk89q.worldedit.cui.CUIPointBasedRegion;
 import com.sk89q.worldedit.cui.CUIEvent;
 import com.sk89q.worldedit.cui.SelectionPointEvent;
 import com.sk89q.worldedit.cui.SelectionShapeEvent;
+import com.sk89q.worldedit.masks.Mask;
 import com.sk89q.worldedit.regions.CuboidRegionSelector;
 import com.sk89q.worldedit.regions.Region;
 import com.sk89q.worldedit.regions.RegionSelector;
@@ -74,6 +75,7 @@ public class LocalSession {
     private boolean beenToldVersion = false;
     private boolean hasCUISupport = false;
     private boolean fastMode = false;
+    private Mask mask;
     private TimeZone timezone = TimeZone.getDefault();
 
     /**
@@ -660,6 +662,7 @@ public class LocalSession {
                 new EditSession(player.getWorld(),
                         getBlockChangeLimit(), blockBag);
         editSession.setFastMode(fastMode);
+        editSession.setMask(mask);
         
         return editSession;
     }
@@ -681,4 +684,22 @@ public class LocalSession {
     public void setFastMode(boolean fastMode) {
         this.fastMode = fastMode;
     }
+
+    /**
+     * Get the mask.
+     * 
+     * @return mask, may be null
+     */
+    public Mask getMask() {
+        return mask;
+    }
+
+    /**
+     * Set a mask.
+     * 
+     * @param mask mask or null
+     */
+    public void setMask(Mask mask) {
+        this.mask = mask;
+    }
 }

src/main/java/com/sk89q/worldedit/commands/GeneralCommands.java

@@ -25,6 +25,7 @@ import com.sk89q.minecraft.util.commands.CommandPermissions;
 import com.sk89q.minecraft.util.commands.NestedCommand;
 import com.sk89q.worldedit.*;
 import com.sk89q.worldedit.blocks.ItemType;
+import com.sk89q.worldedit.masks.Mask;
 
 /**
  * General WorldEdit commands.
@@ -81,6 +82,27 @@ public class GeneralCommands {
         }
     }
 
+    @Command(
+        aliases = {"/gmask", "gmask"},
+        usage = "[mask]",
+        desc = "Set the global mask",
+        min = 0,
+        max = -1
+    )
+    @CommandPermissions({"worldedit.global-mask"})
+    public static void mask(CommandContext args, WorldEdit we,
+            LocalSession session, LocalPlayer player, EditSession editSession)
+            throws WorldEditException {
+        if (args.argsLength() == 0) {
+            session.setMask(null);
+            player.print("Global mask disabled.");
+        } else {
+            Mask mask = we.getBlockMask(player, session, args.getJoinedStrings(0));
+            session.setMask(mask);
+            player.print("Global mask set.");
+        }
+    }
+
     @Command(
         aliases = {"toggleplace"},
         usage = "",