diff --git a/Source/Core/Map/Sector.cs b/Source/Core/Map/Sector.cs
index d6cf0ba1..a6759cca 100755
--- a/Source/Core/Map/Sector.cs
+++ b/Source/Core/Map/Sector.cs
@@ -87,6 +87,7 @@ namespace CodeImp.DoomBuilder.Map
 		//mxd. Rendering
 		private Color4 fogcolor;
 		private SectorFogMode fogmode;
+        private int lastProcessed;
 
 		//mxd. Slopes
 		private Vector3D floorslope;
@@ -142,6 +143,7 @@ namespace CodeImp.DoomBuilder.Map
 		public float FloorSlopeOffset { get { return flooroffset; } set { BeforePropsChange(); flooroffset = value; updateneeded = true; } }
 		public Vector3D CeilSlope { get { return ceilslope; } set { BeforePropsChange(); ceilslope = value; updateneeded = true; } }
 		public float CeilSlopeOffset { get { return ceiloffset; } set { BeforePropsChange(); ceiloffset = value; updateneeded = true; } }
+        internal int LastProcessed { get { return lastProcessed; } set { lastProcessed = value; } }
 
 		#endregion
 
diff --git a/Source/Core/Map/Sidedef.cs b/Source/Core/Map/Sidedef.cs
index 63e07abf..35d1adba 100755
--- a/Source/Core/Map/Sidedef.cs
+++ b/Source/Core/Map/Sidedef.cs
@@ -57,6 +57,9 @@ namespace CodeImp.DoomBuilder.Map
 
 		// Clone
 		private int serializedindex;
+
+        // Rendering
+        private int lastProcessed;
 		
 		#endregion
 
@@ -78,6 +81,7 @@ namespace CodeImp.DoomBuilder.Map
 		public long LongMiddleTexture { get { return longtexnamemid; } }
 		public long LongLowTexture { get { return longtexnamelow; } }
 		internal int SerializedIndex { get { return serializedindex; } set { serializedindex = value; } }
+        internal int LastProcessed { get { return lastProcessed; } set { lastProcessed = value; } }
 		
 		#endregion
 
diff --git a/Source/Core/Map/Thing.cs b/Source/Core/Map/Thing.cs
index 8b650093..660fa26b 100755
--- a/Source/Core/Map/Thing.cs
+++ b/Source/Core/Map/Thing.cs
@@ -86,11 +86,14 @@ namespace CodeImp.DoomBuilder.Map
 		private bool fixedsize;
 		private bool directional; //mxd. If true, we need to render an arrow
 
-		#endregion
+        // Rendering
+        private int lastProcessed;
 
-		#region ================== Properties
+        #endregion
 
-		public MapSet Map { get { return map; } }
+        #region ================== Properties
+
+        public MapSet Map { get { return map; } }
 		public int Type { get { return type; } set { BeforePropsChange(); type = value; } } //mxd
         public GZGeneral.LightData DynamicLightType { get { return dynamiclighttype; } internal set { BeforePropsChange(); dynamiclighttype = value; } }
 		public Vector3D Position { get { return pos; } }
@@ -116,13 +119,14 @@ namespace CodeImp.DoomBuilder.Map
 		public ThingRenderMode RenderMode { get { return rendermode; } } //mxd
 		public bool IsDirectional { get { return directional; } } //mxd
 		public bool Highlighted { get { return highlighted; } set { highlighted = value; } } //mxd
+        internal int LastProcessed { get { return lastProcessed; } set { lastProcessed = value; } }
 
-		#endregion
+        #endregion
 
-		#region ================== Constructor / Disposer
+        #region ================== Constructor / Disposer
 
-		// Constructor
-		internal Thing(MapSet map, int listindex)
+        // Constructor
+        internal Thing(MapSet map, int listindex)
 		{
 			// Initialize
 			this.elementtype = MapElementType.THING; //mxd
diff --git a/Source/Core/VisualModes/VisualMode.cs b/Source/Core/VisualModes/VisualMode.cs
index 16ddbc9d..049eb8f9 100755
--- a/Source/Core/VisualModes/VisualMode.cs
+++ b/Source/Core/VisualModes/VisualMode.cs
@@ -73,8 +73,8 @@ namespace CodeImp.DoomBuilder.VisualModes
 		protected Dictionary<Thing, VisualThing> allthings;
 		protected Dictionary<Sector, VisualSector> allsectors;
 		protected List<VisualBlockEntry> visibleblocks;
-		protected Dictionary<Thing, VisualThing> visiblethings;
-		protected Dictionary<Sector, VisualSector> visiblesectors;
+		protected List<VisualThing> visiblethings;
+		protected List<VisualSector> visiblesectors;
 		protected List<VisualGeometry> visiblegeometry;
 		
 		#endregion
@@ -104,9 +104,9 @@ namespace CodeImp.DoomBuilder.VisualModes
 			this.allsectors = new Dictionary<Sector, VisualSector>(General.Map.Map.Sectors.Count);
 			this.allthings = new Dictionary<Thing, VisualThing>(General.Map.Map.Things.Count);
 			this.visibleblocks = new List<VisualBlockEntry>();
-			this.visiblesectors = new Dictionary<Sector, VisualSector>(50);
+			this.visiblesectors = new List<VisualSector>(50);
 			this.visiblegeometry = new List<VisualGeometry>(200);
-			this.visiblethings = new Dictionary<Thing, VisualThing>(100);
+			this.visiblethings = new List<VisualThing>(100);
 			this.processgeometry = true;
 			this.processthings = true;
 			this.vertices = new Dictionary<Vertex, VisualVertexPair>(); //mxd
@@ -518,9 +518,9 @@ namespace CodeImp.DoomBuilder.VisualModes
 			Vector2D campos2d = General.Map.VisualCamera.Position;
 			
 			// Make collections
-			visiblesectors = new Dictionary<Sector, VisualSector>(visiblesectors.Count);
-			visiblegeometry = new List<VisualGeometry>(visiblegeometry.Capacity);
-			visiblethings = new Dictionary<Thing, VisualThing>(visiblethings.Count);
+			visiblesectors = new List<VisualSector>(visiblesectors.Count * 2);
+			visiblegeometry = new List<VisualGeometry>(visiblegeometry.Count * 2);
+			visiblethings = new List<VisualThing>(visiblethings.Count * 2);
 
 			// Get the blocks within view range
 			visibleblocks = blockmap.GetFrustumRange(renderer.Frustum2D);
@@ -534,7 +534,7 @@ namespace CodeImp.DoomBuilder.VisualModes
 					foreach(Linedef ld in block.Lines)
 					{
 						// Line not already processed?
-						if (ld.LastProcessed != lastProcessed)//if(!visiblelines.Contains(ld))
+						if (ld.LastProcessed != lastProcessed)
 						{
                             // Add line if not added yet
                             ld.LastProcessed = lastProcessed;
@@ -560,6 +560,10 @@ namespace CodeImp.DoomBuilder.VisualModes
 					// Things
 					foreach(Thing t in block.Things)
 					{
+                        if (t.LastProcessed == lastProcessed) continue;
+
+                        t.LastProcessed = lastProcessed;
+
 						// Not filtered out?
 						if(!General.Map.ThingsFilter.IsThingVisible(t)) continue;
 
@@ -575,9 +579,9 @@ namespace CodeImp.DoomBuilder.VisualModes
 							allthings[t] = vt;
 						}
 
-						if(vt != null && !visiblethings.ContainsKey(vt.Thing))
+						if(vt != null)
 						{
-							visiblethings[vt.Thing] = vt;
+							visiblethings.Add(vt);
 						}
 					}
 				}
@@ -630,7 +634,13 @@ namespace CodeImp.DoomBuilder.VisualModes
 		// This finds and adds visible sectors
 		private void ProcessSidedefCulling(Sidedef sd)
 		{
-			VisualSector vs;
+            // Do nothing if we already added it.
+			if (sd.LastProcessed == lastProcessed)
+                return;
+
+            sd.LastProcessed = lastProcessed;
+
+            VisualSector vs;
 			
 			// Find the visualsector and make it if needed
 			if(allsectors.ContainsKey(sd.Sector))
@@ -647,12 +657,12 @@ namespace CodeImp.DoomBuilder.VisualModes
 			
 			if(vs != null)
 			{
-				// Add to visible sectors if not added yet
-				if(!visiblesectors.ContainsKey(sd.Sector))
-				{
-					visiblesectors.Add(sd.Sector, vs);
-					visiblegeometry.AddRange(vs.FixedGeometry);
-				}
+                if (sd.Sector.LastProcessed != lastProcessed)
+                {
+                    sd.Sector.LastProcessed = lastProcessed;
+                    visiblesectors.Add(vs);
+                    visiblegeometry.AddRange(vs.FixedGeometry);
+                }
 				
 				// Add sidedef geometry
 				visiblegeometry.AddRange(vs.GetSidedefGeometry(sd));
@@ -805,7 +815,7 @@ namespace CodeImp.DoomBuilder.VisualModes
 			}
 			
 			// Add all the visible things
-			foreach(VisualThing vt in visiblethings.Values) pickables.Add(vt);
+			foreach(VisualThing vt in visiblethings) pickables.Add(vt);
 
 			//mxd. And all visual vertices
 			if(General.Map.UDMF && General.Settings.GZShowVisualVertices) 
diff --git a/Source/Plugins/BuilderModes/VisualModes/BaseVisualMode.cs b/Source/Plugins/BuilderModes/VisualModes/BaseVisualMode.cs
index 05a49bb9..01d1f065 100755
--- a/Source/Plugins/BuilderModes/VisualModes/BaseVisualMode.cs
+++ b/Source/Plugins/BuilderModes/VisualModes/BaseVisualMode.cs
@@ -1340,7 +1340,7 @@ namespace CodeImp.DoomBuilder.BuilderModes
 					renderer.DrawThingCages = ((BuilderPlug.Me.ShowVisualThings & 2) != 0);
 					
 					// Render all visible things
-					foreach(VisualThing t in visiblethings.Values)
+					foreach(VisualThing t in visiblethings)
 						renderer.AddThingGeometry(t);
 				}
 
@@ -1551,9 +1551,9 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			if(sectordata != null && sectordata.Count > 0) RebuildElementData();
 
 			//mxd. As well as geometry...
-			foreach(KeyValuePair<Sector, VisualSector> group in visiblesectors)
+			foreach(VisualSector sector in visiblesectors)
 			{
-				BaseVisualSector vs = (BaseVisualSector)group.Value;
+				BaseVisualSector vs = (BaseVisualSector)sector;
 				if(vs != null) vs.Rebuild();
 			}
 
@@ -1572,9 +1572,9 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			if(sectordata != null && sectordata.Count > 0) RebuildElementData();
 
 			//mxd. As well as geometry...
-			foreach(KeyValuePair<Sector, VisualSector> group in visiblesectors) 
+			foreach(VisualSector sector in visiblesectors) 
 			{
-				BaseVisualSector vs = (BaseVisualSector)group.Value;
+				BaseVisualSector vs = (BaseVisualSector)sector;
 				if(vs != null) vs.Rebuild();
 			}
 
@@ -3264,7 +3264,7 @@ namespace CodeImp.DoomBuilder.BuilderModes
             foreach (IVisualEventReceiver i in objs)
             {
                 if (i is BaseVisualThing)
-                    visiblethings.Remove(((BaseVisualThing)i).Thing); // [ZZ] if any
+                    visiblethings.Remove((BaseVisualThing)i); // [ZZ] if any
                 i.OnDelete();
             }
             PostAction();
@@ -3305,7 +3305,7 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			foreach(IVisualEventReceiver i in objs) 
 			{
 				BaseVisualThing thing = (BaseVisualThing)i;
-                visiblethings.Remove(thing.Thing); // [ZZ] if any
+                visiblethings.Remove(thing); // [ZZ] if any
                 thing.Thing.Fields.BeforeFieldsChange();
 				thing.Thing.Dispose();
 				thing.Dispose();