anchor.diff:                   Content.staticModelSurface Gen.name
                       [Entity.SurfaceIndex == 1
                        Entity.StaticModel <== field --|> fun field world -> snd (Field.getFieldModelDescriptorsAndAssetTag field world)
  -                     Entity.RenderStyle == Forward 1.0f]]]]
  +                     Entity.RenderStyle == Forward -1.0f]]]]
   
       // here we create the scenery in an imperative fashion
       // NOTE: performance goal: 60fps, current: 57fps.
  
positive.code:                     texCoordses.[u+2] <- v2 texCoordX2 texCoordY2
                      texCoordses.[u+3] <- v2 texCoordX texCoordY
                      texCoordses.[u+4] <- v2 texCoordX2 texCoordY2
                      texCoordses.[u+5] <- v2 texCoordX texCoordY
                  | None -> ()
  
          // make normals array
  
negative.code:                     let tileId = tile.Gid - tileSet.FirstGid
                      let columns = tileSet.Columns.Value
                      let rows = tileSet.TileCount.Value / columns
                      let tileX = tileId % tileSet.Columns.Value
                      let tileY = tileId / tileSet.Columns.Value
                      let texCoordX = single tileX / single columns
                      let texCoordY = single tileY / single rows
                      let texCoordX2 = texCoordX + single tileSet.TileWidth / single tileSet.Image.Width.Value
  