1. Honours Graphics 2008 Session 6

2. Today’s focus Terrain rendering Heightfield generation Level-of-detail for terrain

3. Terrain

4. Terrain, cont. Typically only requires a 2D data set (height field) for rendering purposes Height fields often generated randomly, or pertubed from basic design Rendered using block or continuous level- of-detail algorithms

5. Height fields

6. Height field generation Different approaches to height field generation Includes algorithms that are based on recursive faults, circular alevation, midpoint displacement Often followed by a post-processing step to create a sense of erosion

7. Midpoint displacement

8. Heightfield post-processing Simulated erosion, eliminate artifacts, etc.

9. Terrain rendering Terrain data sets can exceed gigabytes of data, covering millions of data points The large volume of data requires effective level-of-detail handling to reduce to manageable subsets Comes in block or continuous LOD variants

10. Terrain rendering, cont.

11. Block LOD

12. Block LOD, cont.

14. LOD metrics For a LOD scheme it is necessary to define some metric by which the required detail level can be determined Simplest LOD metric: things that are further away require less detail

15. LOD metrics, cont. Typical basic LOD metric considers distance, as well as variance of the underlying structure Variance describes the structural complexity – flat surfaces have a low variance; while complex, articulated surfaces have a high variance

16. LOD metrics, cont. Any number of additional metrics can be considered, for example: FOV metric Silhouette metric Line of Sight metric Actor / entity metric PVS metric

17. Continuous LOD A number of algorithms exist that can create continuously varying level of detail meshes on a per-frame basis In literature sometimes known as TINs (triangulated irregular networks) Includes among others work by Lindstrom, Röttger, and Duchaineau

18. Continuous LOD, cont. Duchaineau, famously, created ROAM Functions by imposing a triangular binary tree on the terrain data and performing split and merge operations on the tree

19. Continuous LOD, cont. ROAM is a frame-coherent algorithm Results from the prior frame can be incrementally changed for the current frame Requires little change in view from prior frame – but reduces computational overhead to 2 to 5% of full computation

20. Continuous LOD, cont. Diamond terrain algorithm, by Hakl Improves on ROAM by changing the underlying structure from a triangle binary tree to a triangle quadtree

21. Continuous LOD, cont. Improves hardware friendliness through generating a mesh that is more tri-strip friendly Requires half the split / merge operations to achieve the same detail level as ROAM

23. Homework Implement a random heightfield generator and display it at various degrees of refinement using a quadtree Due for session 7 …and… project

24. Project Primary project for the course 40% of final mark Implement a traversable terrain renderer, should be able to do the following: LOD scheme FOV culling Sky Due for last session of course