“La mina del diablo”

Posted: July 14, 2011 in Computer Graphics, Physics & Simulation

Abstract

This was a project for my Masters in Computer Graphics, Games and Virtual Reality at URJC.

We were asked to develop some sort of mine train real-time animation from scratch. It had to feature dinamically-generated tunnel bumps with Perlin noise, on-board camera view and three rendering modes: Polygon fill, Wireframe and Points. We chose OpenSceneGraph for the job.

Design tools

As a big fan of rollercoasters I had spent hours on the NoLimits Rollercoaster Simulator which has a quite mature coaster editor. There’s plenty of coasters made with NoLimits around the net, most of them are reconstructions of real ones.

I thought it could be a good idea to be able to load coaster models in NoLimits (.nltrack) format as it would allow us to design the track and the scene in a visual way using the NL Editor.

The .nltrack format is binary and not documented. It contains the shape of the track as control points of cubic Bezier curves. It also contains info about the colors, supports, external .3DS objects and info about the general appearance of the rollercoaster.

Using Hexplorer and the NL editor itself I was able to figure out the control points and the location/scaling/rotation of the external 3D models. Later I discovered that there’s a library called libnltrack, which helped a lot.

My pal Danny modeled a couple of rooms, an outdoor scene and a lot of mine props (barrels, shovels, …). Then he imported them into the editor and laid out a coaster track passing trough all of the scene.

Coaster geometry

Correct generation of the rails and the crossbeams for the track was a bit of a challenge, and it needed to be efficient!.

I came up with a solution based on the concept of a “slider”, a virtual train which can be placed at any place around the track (just specifying how many kilometers away from the origin (the station) it would be), and it returns three orthonormal vectors forming a base which was then used to transform vertices to the train’s POV.

By using two sliders, one ahead of the other one can set vertices back and forth to form triangle strips in order to generate perfectly stitched cylinders. I ran into a couple of problems when the track was almost vertical but I finally managed to solve them.

Upon startup, the geometry for the whole coaster is generated. The engine generates about 15 meters of track per geode, this way OpenSceneGraph is able to cull the out-of-sight track segments efficiently. Besides, two levels of detail are generated based on the distance to the camera.

As for the crossbeams, it’s just a .3ds model which is repeatedly placed along the track.

Tunnels

The program generates a 256×256 grayscale perlin noise texture which is then used as a displacement mapping for a cylinder mesh generated around the track on load time.

The editor is able to mark segments as ‘tunnel’ easily turning tunnels on or of in a per-segment basis.

The meshes are also segmented for better culling and stitched together. They have a diffuse rock and floor texture applied.

Train

The train is a .3DS model by Danny which has a slider assigned to it and its animated following an extremely simple phyisics scheme based on the potential energy of the train. It has a spotlight on the front so the track, rooms and tunnels are illuminated as the train goes trhough. Moreover the illumination of the train mesh is switched from the sunlight to the spotlight based on wether it’s in a tunnel or not.

Effects

A skydome, lens flare (props to Tomás), and OSG’s impementation of shadow mapping were added in.

Audio and others

In the last minute before the deadline, supports for the track were generated as regularly-placed cylinders, but unfortunately that wasn’t there yet at the time the screenshots and the videos were taken.

A white noise audio file is played with a pitch and volume proportional to the train speed.

To be done

Due to the tight timing constraints we were subject to I was forced to leave a lot of things to be done, among them:

– Per-pixel lighting.

– Post-processing effects (vignette and HDR)

 

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Comments
  1. Ercan Akyürek says:

    If you want better track models and more, check this tutorial out: http://www.youtube.com/watch?v=YCLQ1j_EAmU

    – Ercan (libnltrack creator)

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