Previously, Daggerfall Modelling used a one-dimensional array of objects and looped through them to draw scenes. This is fine for small environments but doesn’t scale up very well.  It also makes visibility testing and render batching harder than it needs to be. When it came time to link up the levers and switches, I realised it was time to put in a scene graph.

I decided to use a simple Bounding Volume Hierarchy based around spheres. The beauty of bounding spheres is that you don’t have to worry about axis alignment as you do with boxes. Spheres may not wrap objects quite as tightly, but they’re a lot easier to handle when transformed (rotated, translated, scaled, etc.) as the volume is always the same shape and alignment in 3D space.

On the left are a couple of screen-shots of the bounding volumes, rendered as wireframe spheres. The root node is red, general models are white, and sprites are green. Resources are added to the scene from the top down, with renderable objects like models and sprites in the leaves of the tree. This hierarchy makes it easy to cull non-visible groups – if a node isn’t visible, then none of its children can be visible either. It also simplifies mouse picking and collision as these tests are only performed where necessary. Batching visible polygons by texture becomes easier, which greatly improves rendering times. And finally, linking up chained action records becomes simplified thanks to each scene node being a discrete class aware of its own state.

Certain objects in Daggerfall have action records that describe how this object can move, rotate, etc. An example every Daggerfall player will be familiar with is the throne room in Privateer’s Hold (pictured left). When you throw the switch an action record makes the lever rotate, which chains to another action record to make the platform rise, which finally chains to the throne to make it rise also. The end result is you throw the switch and the platform rises (along with the throne and the player).

If you open up the screenshot to the left, you will see a red line going from switch, to platform, to throne. This is the action chain linking the objects together. The next screenshot shows the same linkage in Mantellan Crux – from the axe on the floating island, to the crossbow, to the giant sword. At some point, I will number the nodes so it becomes easier to visualise where action chains begin and end.

In Daggerfall Modelling Beta 1 it will be possible to trigger action chains and watch the animations run. There are other actions, such as teleporting the player or casting spells, but I am only going to support action that cause things to move around the scene.

Once gravity and collision are implemented, you will be able to explore dungeons from a first-person perspective with the ability to operate doors and platforms. You can also just turn off collision and gravity to fly around the scene with total freedom.

The renderer in XNALibrary can plug in components that add functionality. This is quite basic at the moment, but will be extended down the road as needed.

Currently, the add-ins are a billboard manager for rendering sprites like trees, animals, NPCs, and a sky manager for drawing the background sky in location exteriors. You can see these components in action to the left.