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== Tiled Display ==
ParaView’s parallel architecture makes it possible to visualize massive amounts of data interactively. When the data is of sufficient resolution that parallel processing is necessary for interactive display, it is often the case that high-resolution images are needed to inspect the data in adequate detail. If you have a 2D grid of display devices, you can run ParaView in tiled display mode to take advantage of it.
To put ParaView in tiled display mode, give pvserver (or pvrenderserver) the X and Y dimensions of the 2D grid with the ''--tile-dimensions-x'' (or ''-tdx'') and ''--tile-dimensions-y'' (or ''‑tdy'') arguments. The X and Y dimensions default to 0, which disables tiled display mode. If you set only one of them to a positive value on the command line, the other will be set to 1. In tiled display mode, there must be at least as many server (in client / server mode) or render server (in client / data server / render server mode) nodes as tiles. The example below will create a 3x2 tiled display.
''pvserver -tdx=3 -tdy=2''
Unless you have a high-end display wall, it is likely that each monitor's bezel creates a gap between the images shown in your tiled display. You can compensate for the bezel width by considering them to be like mullions on a window. To do that, specify the size of the gap (in pixels) through the ''--tile-mullion-x'' (''-tmx'') and ''--tile-mullion-y'' (''-tmy'') command line arguments.
The IceT library, which ParaView uses for its image compositing, has custom compositing algorithms that work on tiled displays. Although compositing images for large tiled displays is a compute-intensive process, IceT reduces the overall amount of work by employing custom compositing strategies and removing empty tiles from the computation, as demonstrated in Figure 13.5. If the number of nodes is greater than the number of tiles, then the image compositing work will be divided amongst all the processes in the render server. In general, rendering to a tiled display will perform significantly better if there are many more nodes in the cluster than tiles in the display it drives. It also greatly helps if the geometry to be rendered is spatially distributed. Spatially distributed data is broken into contiguous pieces that are contained in small regions of space and are therefore rendered to smaller areas of the screen. IceT takes advantage of this property to reduce the amount of work required to composite the final images. ParaView includes the D3 filter, which redistributes data amongst the processors to ensure a spatially distributed geometry and thus improves tiled rendering performance.
[[File:ParaView_UsersGuide_TileComposite.png|thumb|center|800px|'''Figure 13.5''' Compositing images for 8 processes on a 4-tile display]]
Unlike other parallel rendering modes, composited images are not delivered to the client. Instead, image compositing is reserved for generating images on the tiled display, and the desktop renders its own images from a lower resolution version of the geometry to display in the UI. In Tiled Display Mode, ParaView automatically decimates the geometry and sends it to the client to make this happen. However, when the data is very large, even a decimated version of the geometry can overwhelm the client. In this case, ParaView will replace the geometry on the client with a bounding box.
You have several controls at run-time over the tiled rendering algorithm that you can tune to maintain interactivity while visualizing very large data on very high-resolution tiled displays. These are located on the Tile Display Parameters section of the Render View / Server page of the application settings dialog. These controls are described in the [[ParaView/ Users_Guide/ Settings | Application Settings]] section of the Appendix.