Overhang Terrain Scene Manager for OGRE, a volume-rendered paged terrain library featuring Transvoxel
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Example Resetting camera position to origin and setting the light source to a… Jun 8, 2014
OhTSM
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README.md

README.md

OverhangTerrainSceneManager (OhTSM) - Volume Rendered Terrain Paging Engine

Version: 0.2a Contributors: Jonathan Neufeld (http://www.extollit.com) Original Author: Martin Enge (martin.enge@gmail.com) Credit: Transvoxel by Eric Lengyel (http://www.terathon.com/voxels/)

Description

This is a volumetric terrain rendering library that supports paging. It is based on the old OverhangTerrainSceneManager library originally written by Martin Enge. It has been modified to use the Transvoxel algorithm for multi- resolution isosurface stitching. If you are familiar with legacy OverhangTerrainSceneManager see CHANGES (below).

NOTE: Please review the KNOWN ISSUES (below) before using this library

MODULES

Example(OhTSM)

This is a sample application that demonstrates the OverhangTerrainSceneManager library with simple waveform-generated terrain using a straight blue material. Click with the left mouse-button to dig and right mouse-button to build. Use the keys W.A.S.D. to move around the scene.

OhTSM

This is the OverhangTerrainSceneManager library. Files in the "Core Sources" and "Core Headers" folders are internal APIs whereas the "Header Files" and "Source Files" folders are meant to be public-facing.

CHANGES

There are many difference from this version of OverhangTerrainSceneManager from the legacy version originally written by Martin Enge. More than 90% of the codebase has been rewritten to facilitate the use of Transvoxel and concurrent page loading.

  • There are no height-map terrain renderables anymore, heightmaps are converted into voxel data and isosurfaces are extracted from them. This was necessary to overcome the impossibly complex challenges of multi- resolution stitching between isosurfaces and non-isosurface renderables.
  • IsoSurfaceBuilder has been completely rewritten to use Transvoxel
  • Code for plugging into an editor has been dropped
  • Terrain material logic has been dropped, library users are fully responsible for supplying materials for the terrain
  • Dynamic WorkQueue-based terrain paging and serialization
  • The scene manager no longer inherits from OctreeSceneManager, the octree doesn't play nice with dynamic paged terrain
  • Voxel data is preserved for each isosurface and compressed using RLE compression rather than relying on dynamically populating a singleton voxel grid from meta objects for each query, which would be prohibitively expensive
  • Isosurface metadata is preserved for fast generation of multiple resolutions
  • New vertices from new stitch configurations of the same resolution for an isosurface are appended to the same hardware vertex buffer rather than replacing its contents completely
  • Geomorphing has been dropped
  • Metaball voxelization algorithm uses a different formula than the one recommended by Geiss (http://www.geisswerks.com/ryan/BLOBS/blobs.html)

KNOWN ISSUES

(09-Jun-2014)

  • Geometry batching improved, now only one vertex and index buffer per surface

(10-May-2013)

  • Only ray scene queries are supported, other types of scene queries are not implemented yet
  • Some shading problems along transition cell seams due to incorrect normal calculation
  • Geometry batching is rather high resulting in a choppy render frame rate
  • Only metaballs are currently supported for volumetric deformation
  • Volumetric deformation performance is inconsistent possibly related to geometry batching, it is fastest for example when digging straight downward and beneath the ground some
  • Geomorphing between resolutions is not supported
  • Some cracks appear between two adjacent surfaces when the LOD difference between them is greater than one, this is due to a simplistic LOD calculation algorithm
  • Gradient normal calculation is the only reliable method for producing geometry with the least shading artefacts, weighted average and average normal calculation does not take into account adjacent isosurface geometries
  • Transition cell geometry erratic and current implementation of Transvoxel's response to this (Lengyel p.39) actually makes the problem worse
  • Threading and concurrency has had only limited testing, race conditions may exist
  • Adding meta objects to the scene may touch more terrain pages than is necessary
  • No versioning or CRC check on terrain serialization / deserialization
  • Clean-up is a little klunky, Ogre::WorkQueue doesn't appear to support waiting on task completion
  • Texture-coordinates are not properly implemented, most obvious solution is to employ (expensive) triplanar texturing
  • Ray queries sometimes fail, unclear why this is, behavior is inconsistent
  • Material-per-tile not tested, might even be non-functional
  • Loading or changing main top-level configuration options during runtime has no impact on the scene, there is no business logic to re-initialize the scene and/or dependencies
  • Iteration through meta-fragments is not public-facing, only used for internal purposes
  • Meta balls do not account for terrain group origin

INSTALLATION

Prerequisites:

  • OGRE 1.7
  • Visual Studio 2010

A good understanding of and familiarity with the OGRE SDK is a prerequisite to using this library. OverhangTerrainSceneManager was built against OGRE v1.7. The Visual Studio development environment depends on the settings of the following environment variables each of which points to a path on disk:

  • DXSDK_DIR: Location of your DirectX SDK
  • BOOST_HOME: C++ Boost library used by OGRE
  • OGRE_SRC: OGRE source files and includes including "lib/Debug" and "lib/Release" subfolders
  • OGRE_DEPS: Home directory of OGRE dependencies including "lib/Debug" and "lib/Release" subfolders