OGRE
1.11.6
Object-Oriented Graphics Rendering Engine
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Welcome to the Volume Component of OGRE. It is a component to render volumes. It can handle any volume data but featurewise has a tedency towards terrains. The terrain aspect means, that it's all about huge meshes being displayed with high performance via a level of detail mechanism. Thanks to volume rendering, caves, cliffes, holes and similar geometry can be displayed. Also constructive solid geometry gets easy.
A dense list of the features:
This documentation is only intended for the usage of the Volume Component, not the algorithms which make it work. If you want to get to know the theory behind it, you can read the articles on this page: http://volume-gfx.com/
Here is an example loading the volume scene from a configuration file. The configuration file must be findable by the resource system of course. Only "OgreVolumeChunk.h" has to be included.
The first line creates the volume chunk which is the MovableObject holding the Volume-Root. Next, a SceneNode is created where the volume(-tree) is attached to. And lastly, the volume is loaded from the configuration file "volumeTerrain.cfg". mSceneMgr is the SceneManager who should show the volume. Later, when you don't need it anymore, you have to free the volumeRoot Chunk via OGRE_DELETE.
This example skips the configuration file and loads a simple CSG-Scene: An union of a 3D Texture and a sphere with 5 LOD levels. It also setups a material LOD system. First, create a sphere with the radius 5 at the coordinates 128, 150, 128:
Now a 3D texture from "volumeTerrainBig.dds" which has the world dimensions 256, 256, 256. The next flag indicates that the trilinear interpolation of the value-selection should be activated. We switch off the trilinear interpolation and the sobel filter of the normal for the sake of faster loading times:
Now combine them:
Set the general parameters, see the comments for their meaning:
Create the root-chunk and load now. The two vectors define the area to be scanned in the volume-source. The following integer determines the amount of LOD-levels.
Now setup the global volume material:
When you want to integrate the volume triangles in a physics engine for example, you need to hand over the exact triangles. For this scenario, the ChunkParameters hold a pointer to a ''MeshBuilderCallback'' and a number ''lodCallbackLod''. The first is an interface with a single function ''trianglesReady'' which is called, when the triangles of a chunk are ready. The chunks are chosen via the ''lodCallbackLod''. If you build a volume with 3 LOD levels and you want the triangles of the highest detail level, you set this parameter to 3. Example:
And using it like this:
Or in case of loading from a configuration file:
You might have seen, that a pointer to a SimpleRenderable is handed in, too. This is actually the Chunk whose triangles are loaded. It's parent class is used to not create a circular dependency. You might get the triangle data from it, too by getting the Renderoperation.
When you want to do something exactly on the volume surface, you can cast rays and find their first intersection point. Behold that the triangle representation might be slightly different than the actual volume surface. And you have to scale the ray origin just like the volume. Here is an example which uses the negative z-axis of the camera as ray as it might be done like in an ego-shooter:
A usecase is realtime editing of volume terrain as seen as in the sample. Let's union the terrain with a sphere of the radius 2.5 and the center 123/123/123. volumeRoot is the Chunk instance with which the terrain was initially loaded. The factor 1.5 is just to have a save border arround the sphere which also gets updated. The rest of the parameters are 5 LOD levels and a volume mesh covering an area of 384^3.