Collision Testing
Collision testing is done using BoundingObjects, a specific class of Node. There are currently four kinds of BoundingObjects.
- BoundingAABB - An axis-aligned bounding box (or cube). An AABB cannot rotate (or rather, rotating it makes for a differently sized cube that is still axis-aligned).
- BoundingCapsule - A capsule, which can rotate and has a customizeable radius and height.
- BoundingSphere - A 3D sphere, with customizeable radius.
- BoundingTriangles - A triangle mesh, primarily used for terrain or other static objects.
NOTE: Currently, AABB > Triangles and Triangles > Triangles collisions are buggy.
To check for collisions, you simply call BoundingObject.Colliding(otherBounds) to see if an object is intersecting with another. You can also get more detail with BoundingObject.Collision(otherBounds), which returns a Collision struct.
A Collision is the result of at least one intersection between two BoundingObjects. Each Intersection struct contains information regarding an intersection between the two Bounds objects, like the contact point, the collision normal, the slope, and the MTV (or minimum translation vector). You can use the MTV to easily move the intersecting object away from the other object. You can also get a few averaged values from the Collision struct itself.
You can also check against multiple objects at the same time using BoundingObject.CollisionTest() or BoundingObject.CollisionTestVec(). Both of these functions allow you to also check for a collision if a BoundingObject were to move in a specific direction. This can be very useful if you want to check for an object in a specific direction, for example (i.e. check downwards for a floor in a platform game).
While not currently implemented yet, ray testing would also be very useful to add and is on the todo list.
There are two ways to create bounding objects in Tetra3D - one way is to do so in code, by simply creating the desired Node and adding it to the node tree. Assuming you use Blender, the other way is to do so from Blender directly. If you install the Blender Add-on, you can specify the Bounds type of an object in Blender, which will then be instantiated as a child underneath the object when creating the scene. See the Blender Add-on page for more information.
In terms of performance, in descending order of efficiency, bounding collision types can be ranked as follows:
BoundingSphere > BoundingCapsule > BoundingAABB > BoundingTriangles
Being that BoundingSpheres are the most efficient collision shape, if you can use BoundingSpheres for collision testing, do so.
Broadphase collision has been added for AABB+BoundingTriangles, Capsule+BoundingTriangles, and Sphere+BoundingTriangles collision checks. The basic idea behind this is to avoid checking for collision against triangles if they're simply too far away from the colliding object. This is done by checking the colliding object against a broadphase AABB at various grid positions surrounding the triangle mesh; if the colliding object collides with the broadphase AABB object at these positions, then we can check the triangles therein for collision. If not, then we can skip those triangles.
By default, the Broadphase grid is broken up into large squares, each of which are about 20 Blender Units large. Note that the grid divisions don't change in size depending on the triangle mesh's dimensions - the grid's overall size changes to cover the triangle mesh, but the cube's divisions would still be 20 Blender Units large (so if your triangle mesh is 19x10x13 Blender Units, you'll have exactly one 20x20x20 cube. Conversely, if your mesh is 50x10x100, you'll have 3 * 1 * 100 = 300 cubes).
You can customize this, though - if you have, for example, a rather large triangle mesh with relatively few triangles, you might desire a coarser broadphase grid, perhaps one where each cell covers 100 Blender Units, rather than just 20. Having a larger grid would allow you to check a small number of triangles while also not checking a huge number of cubes in the broadphase.
To customize the broadphase settings, you can alter the broadphase grid's cell size, either in code with BoundingTriangles.Broadphase.Resize() (which takes both the desired cell size), or in Blender, by checking the "Custom Broadphase Size" checkbox next to the bounds dropdown and then customizing the grid's cell size. You can turn off the broadphase checks by resizing the broadphase using 0 for both values, or calling BoundingTriangles.DisableBroadphase().
