Texture tile visibility determination for dynamic texture loading

Three-dimensional scenes have become an important form of content deliverable through the Internet. Standard formats such as Virtual Reality Modeling Language (VRML) make it possible to dynamically download complex scenes from a server directly to a web browser. However, limited bandwidth between servers and clients presents an obstacle to the availability of more complex scenes, since geometry and texture maps for a reasonably complex scene may take many minutes to transfer over a typical telephone modem link. This paper addresses one part of the bandwidth bottleneck, texture transmission. Current display methods transmit an entire texture to the client before it can be used for rendering. We present an alternative method which subdivides each texture into tiles, and dynamically determines on the client which tiles are visible to the user. Texture tiles are requested by the client in an order determined by the number of screen pixels affected by the texture tile, so that texture tiles which affect the greatest number of screen pixels are transmitted first. The client can render images during texture loading using tiles which have already been loaded. The tile visibility calculations take full account of occlusion and multiple texture image resolution levels, and are dynamically recalculated each time a new frame is rendered. We show how a few additions to the standard graphics hardware pipeline can add this capability without radical architecture changes, and with only moderate hardware cost. The addition of this capability makes it practical to use large textures even over relatively slow network connections.