Kein Folientitel

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Hardware-Accelerated Terrain Rendering by
Adaptive Slicing
Stefan Roettger and Thomas Ertl
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Outline of the Talk

• 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

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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

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Terrain Slicing

• Solution Render arbitrary x-,y-, or z-aligned
  slices
• Assign elevation as primary alpha
• Use texture combiners to subtract texture alpha
  from primary alpha
• Enable alpha test to cut off pixels with alphagt0

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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

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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

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Results

• Approximately 30 fps on a PC with GeForce2 MX
  (640x480)
• CPU is offloaded efficiently (loadlt24)

Slices
Triangles
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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
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Fin
Questions?
http//wwwvis.informatik.uni-stuttgart.de/roettge
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