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[CIS565 2015F] Ray Marching

GLSL Ray Marching

University of Pennsylvania, CIS 565: GPU Programming and Architecture, Project 5

  • Guan Sun
  • Tested on: Google Chrome 46.0.2490.71(64-bit) on Mac OS X Yosemite 10.10.5, Intel Core i7 @ 2.3GHz 8GB, GeForce GT 650M 1024MB (Personal Laptop)

Live on Shadertoy

Acknowledgements

This Shadertoy uses material from the following resources:

  • {McGuire} Morgan McGuire, Williams College. Numerical Methods for Ray Tracing Implicitly Defined Surfaces (2014). PDF
  • {iq-prim} Iñigo Quílez. Raymarching Primitives (2013). Shadertoy
  • {iq-terr} Iñigo Quílez. Terrain Raymarching (2007). Article
  • {iq-rwwtt} Iñigo Quílez. Rendering Worlds with Two Triangles with raytracing on the GPU (2008). Slides
  • {Ashima} Ashima Arts, Ian McEwan, Stefan Gustavson. webgl-noise. GitHub

Project Description:

In this project, a WebGL ray marcher is implemented in an online shader editor Shadertoy using GLSL. The implemented features include,

  • Two ray marching methods
    • Naive ray marching (fixed step size) {McGuire 4}
    • Sphere tracing (step size varies based on signed distance field) {McGuire 6}
  • 4 different distance estimators {McGuire 7} {iq-prim}
    • With normal computation {McGuire 8}
  • One simple lighting computation (Lambert).
  • Soft shadowing using secondary rays {iq-prim} {iq-rwwtt p55}
  • Union operator {McGuire 11.1}
  • Debug views
    • Distance to surface for each pixel
    • Normal direction

Redering result

Debug views

  • Depth view

  • Normal view

Analysis

I implemented both naive ray marching and sphere tracing, the perfomance of them are,

  • Naive ray marching: 18.5 FPS
  • Sphere tracing: 57.3 FPS

It is clear that sphere tracing has a much better rendering perfomance, the reason is it uses a singed distance funtion to adjust the size of each step of the ray cast, thus need much fewer iterations than the naive ray marching which use a fixed step size.