Nightly Forest Scene with Fire

Alex Ehm

CPE 471 - Fall 2016

Final Project

Description

For my final project I created a scene that displays a nightly forest with a fire, in which the user can move freely with a first-person perspective.

Features

Fire

The fire is rendered using a particle system. The particiles are moving upwards with a random velocity per particle, and are moved sideways by a wind velocity. Additionally each particle is moved by a Fractal Noise based on Perlin Noise. The original paper on Perlin Noise gives a very detailed description of Perlin Noise.

Each particle is textured using a alpha texture from a texture atlas containing 16 different textures. The texture is chosen dependent on the progress of the particles lifetime. In addition to that the size of the particles is scaled dependend on the distance of the camera position to the fire, so the fire looks always the same, no matter how far the user is away.

Lighting

One of the key factors to make the scene look nightly is the lighting implementation. There are two different lights in the scene. One is a point light source at the location of the fire and the other is a spotlight that is bound to the users view direction and therefore gives the user the feeling of having a flashlight.

For both light sources the lighting is implemented as Phong shading, including a distance falloff, while the color of each fragment is mixed by its actual color and its color converted to greyscale dependend on the distance falloff. This simulates very well how the human perception works in a dark surrounding.

Additionally the light source in the fire can move around by a small value, to simulate the flickering light a fire would cause in the real world.

Skybox

The scene is enclosed by a skybox displaying a night sky. This is implemented by using OpenGLs cubemap sampler, and is very crucial for the night "feeling" for the user. The cubemap is scaled far bigger than the area in which the user is able to move, so the user can never see the edge where the ground plane is colliding with the cubemap.

Movement

The user can use the WASD-Keys to move in the scene, Spacebar to jump and the mouse to look around.

Screen Capture

Takeaways

• Use a big and well tested library like assimp for loading models. I used tiny obj loader, as I was used to it from the classes, but loading materials and textures with it did not work out with my models.
• Finding good (and free) 3d models is not easy. Most free models are just "teaser models" that are ment to make you buy the the full model pack, and do very often not contain any textures or even materials.
• Having real shadows (not only shading) is curcial for the having a good user experience in an interactive scene. I did not add shadows, as with having the fire as a local lightsource this would at least require omnidirectonal shadow maps.
• Particle systems are not state of the art for rendering fire in real applications. It is a nice project to play around with, but if you are intrested in current methods take a look at NVIDEA Flameworks or one of the many research papers that use a physically-based method to render fire
• Particle systems with a lot of particles need a lot of computing power. With over 2500 particles the framerate of my application dropped under 60 fps, on a system with a Intel Core i7 6700k and a NVIDEA 970M with 6GB GDDR5.

Download

The project can be found on github. The project is build using cmake and requires GLFW and GLEW.

References

Project base code was provided by Zoe Wood.

The Perlin Noise implementations that is used in my project.

The cubemapping tutorial I used.

A very good tutorial on spotlights in OpenGL.