GSWall: A Scalable Tiled-Display Wall

Nirnimesh (homepage)

Tiled displays can provide high resolution and large display area. Cluster-based tiled displays are cost-effective and scalable. Chromium is a popular software API used to build such displays; Chromium based tiled displays tend to be network-limited affecting the scalability in the number of nodes and the ability to handle large environment models. This thesis presents a tiled Display Wall setup based on a client-server architecture, with the server managing all the aspects leaving the clients with rendering as their sole responsibility. Our system uses off-the-shelf graphics hardware and standard ethernet net- work. High-level scene structure and hierarchy of a scene graph (OpenSceneGraph) is used by a central server to minimize network load. The view-frustums of the rendering nodes are treated hierarchically as well. A novel algorithm combines the object hierarchy of the scene graph with the hierarchy of frustums to determine the optimal process of unfolding the hierarchies so as to minimize the number of computations involved. Visible parts of the scene graph are transmitted and cached by the clients to take advantage of temporal coherence. The server, following a push-philosophy, is able to exploit the high degree of overlap in the computation space for each rendering node to avoid concurrent redundant com- putations. We use a multicast oriented protocol for data-transmission to the clients, making the system scalable. Geometry push philosophy from the server helps keep the clients in sync with one another and facilitates the pipelining of the constituent stages. Distributed rendering allows the display wall to be able to render scenes which are otherwise too bulky for any of the individual rendering nodes. No node, including the server, needs to render the entire environment, making our system suitable for interactive rendering of massive models. We show performance measures for the different underlying aspects of our display wall. The display wall application is implemented as a library-intercept mechanism to seam- lessly render any OpenSceneGraph-based graphics application to a tiled-display wall without the need of modification, recompilation or even relinking. This makes our display wall easy to use for several already existing applications. Our studies show that the server and network loads grow sub-linearly with the number of tiles. This makes our scheme suitable for the construction of very large-resolution displays.

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