Game Development Reference
In-Depth Information
6
II
Progressive Screen-Space
Multichannel Surface Voxelization
Athanasios Gaitatzes and Georgios Papaioannou
6.1
Introduction
An increasing number of techniques for real-time global illumination effects rely
on volume data. Such representations allow the fast, out-of-order access to spa-
tial data from any deferred shading graphics pipeline stage as in [Thiedemann et
al. 11, Mavridis and Papaioannou 11, Kaplanyan and Dachsbacher 10]. For dy-
namic environments where both the geometry of the scene and the illumination
can arbitrarily change between frames, these calculations must be performed in
real time. However, when the per frame time budget is limited due to other,
more important operations that must take place while maintaining a high frame
rate, the fidelity of full-scene voxelization has to be traded for less accurate but
faster techniques. This is especially true for video games, where many hun-
dreds of thousands of triangles must be processed in less than 2-3 ms. In this
chapter we present the novel concept of progressive voxelization ,anincremental
image-based volume generation scheme for fully dynamic scenes that addresses
the view-dependency issues of image-based voxelization within the above time
constraints.
Screen-space volume generation methods provide very fast and guaranteed
response times compared to geometry-based techniques but suffer from view-
dependency. More specifically, any technique that is performed entirely in screen
space (as in deferred shading) considers only geometry that has been rendered
into the depth buffer and thus has the following strong limitations: First, it
ignores geometry located outside the field of view. Second, it ignores geometry
that is inside the view frustum but occluded by other objects. Yet these geometry
parts may have a significant influence on the desired final result (see our indirect
illumination case study in this article).
In single-frame screen-space voxelization, volume attributes already available
as fragment data in view-dependent image buffers are transformed and rasterized
 
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