Transcript Kein Folientitel

Hardware-Accelerated
Terrain Rendering
by Adaptive Slicing
Stefan Roettger and Thomas Ertl
Visualization and Interactive Systems Group, University of Stuttgart
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Outline of the Talk
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Previous work by Sim Dietrich (NVIDIA)
Terrain slicing approach
Rasterization of horizontally aligned slices
Rasterization of arbitrary slices
Adaptive determination of number of slices
Hybrid approach (slicing / polygonal rendering)
Results
Conclusion
Visualization and Interactive Systems Group, University of Stuttgart
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Previous Work
• NVIDIA white paper by Sim
Dietrich
• Store elevation in alpha
channel of texture map
• Render set of horizontally
aligned slices
• Use alpha test to render only
the solid parts of the terrain
• Artifacts for low view points
Visualization and Interactive Systems Group, University of Stuttgart
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Terrain Slicing
• Solution: Render
arbitrary x-,y-, or zaligned slices
• Assign elevation as
primary alpha
• Use texture combiners
to subtract texture alpha
from primary alpha
• Enable alpha test to cut
off pixels with alpha>0
Visualization and Interactive Systems Group, University of Stuttgart
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Sub-Pixel Exactness
• Split terrain into several tiles
• Foreach tile:
– Determine whether x-,y-,
or z-slices are needed
– Estimate the number of
parallel slices to achieve
sub-pixel exactness (by
screen space projection of
inter-slice distance)
– Rasterize the slices
Visualization and Interactive Systems Group, University of Stuttgart
Page 5
Hybrid Approach
• Use a hierarchical quadtree representation
of the terrain to optimally adapt the number
of drawn slices to the viewing distance
• At each node check whether slicing of the
actual node or the four children is faster
cost = #slices (#pixels + #vertices)
• At each leave node check whether terrain
slicing or polygon rendering would be
faster and choose the appropriate method
Visualization and Interactive Systems Group, University of Stuttgart
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Results
• Approximately 30 fps on a PC with GeForce2 MX (640x480)
• CPU is offloaded efficiently (load<24%)
Slices
Triangles
Visualization and Interactive Systems Group, University of Stuttgart
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Conclusion
• Rendering performance
depends mainly on screen
size (rasterization bound)
• Rendering performance does
not depend on the size of the
height field
• Algorithmic complexity is
low in comparison to C-LOD
approaches
• Well suited for displacement
maps or small radar views
Aquanox
Visualization and Interactive Systems Group, University of Stuttgart
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Fin
Questions?
http://wwwvis.informatik.uni-stuttgart.de/~roettger
Visualization and Interactive Systems Group, University of Stuttgart
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