Rendering on a Budget:
J. T. Klosowski
C. T. Silva
A Framework for Time-Critical Rendering
pages 115-122, October, 1999
We present a technique for optimizing the rendering of high-depth
complexity scenes. Prioritized-Layered Projection (PLP) does this by
rendering an estimation of the visible set for each frame. The novelty
in our work lies in the fact that we do not explicitly compute visible
sets. Instead, our work is based on computing on demand a
priority order for the polygons that maximizes the likelihood of
rendering visible polygons before occluded ones for any given
scene. Given a fixed budget, e.g. time or number of
triangles, our rendering algorithm makes sure to render geometry
respecting the computed priority.
There are two main steps to our technique: (1) an occupancy-based
tessellation of space; and (2) a solidity-based traversal algorithm.
PLP works by computing an occupancy-based tessellation of space, which
tends to have smaller cells where there are more geometric primitives,
e.g., polygons. In this spatial tessellation, each cell is assigned a
solidity value, which is directly proportional to its likelihood of
occluding other cells. In its simplest form, a cell's solidity value
is directly proportional to the number of polygons contained within
it. During our traversal algorithm, cells are marked for projection,
and the geometric primitives contained within them actually
rendered. The traversal algorithm makes use of the cells' solidity,
and other view-dependent information to determine the ordering in
which to project cells. By tailoring the traversal algorithm to the
occupancy-based tessellation, we can achieve very good frame rates
with low preprocessing and rendering costs.
In this paper, we describe our technique and its implementation in
detail. We also provide experimental evidence of its performance and
briefly discuss extensions of our algorithm.
Index Terms: Polygon rendering, visibility ordering, occlusion culling
Click on the image to see an animation (1MB) of PLP's traversal
We illustrate the nature of PLP's traversal algorithm in a 2D example.
PLP will render geometry up to a fixed budget (of time or geometry).
The different colors represent:
- White: the input geometry (2D line segments)
- Blue: the spatial tessellation (a Delaunay triangulation)
- Red: the rendered geometry (and view frustum)
- Green: the cells in tessellation considered most likely
visible (whose geometry gets rendered)
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