Honours Graphics 2008 Session 6

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

Terrain

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

Height fields

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

Midpoint displacement

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

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

Terrain rendering, cont.

Block LOD

Block LOD, cont.

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

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

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

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

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

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

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

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

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

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