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Path Tracing Michael Fogleman September 2015 a.k.a. sweet graphics

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The Code speakerdeck.com/fogleman github.com/fogleman/pt These Slides

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Path tracing is a realistic rendering algorithm that simulates light bouncing around a scene.

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“Global illumination” takes into account not only the light which comes directly from light sources (direct illumination), but also light rays that are reflected by other surfaces (indirect illumination). “Path tracing” falls under the umbrella of “global illumination” algorithms.

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The “Rendering Equation” Uhh…

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The “Rendering Equation” • Its own light output (emittance), and • The sum total of reflected light from all directions In layman’s terms, an object’s color depends on:

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Monte Carlo • Path tracing is a randomized “Monte Carlo” algorithm • Simulate billions of random light rays bouncing around the scene • Hundreds or thousands of rays per pixel • Random = different results each time you run it • More rays = less noise in the image

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Basic Algorithm • For each pixel: • Cast a ray from the camera and through the pixel • Determine the nearest object in the scene that the ray intersects • Cast shadow ray(s) to determine direct lighting • Recursively cast more rays to determine indirect lighting, until some maximum depth is reached

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Bounces (Recursion Depth)

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Bounces: 0

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Bounces: 1

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Bounces: 2

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Bounces: 3

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Bounces: 4

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Bounces: 8

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Bounces: 16

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Noise

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Iterations: 1

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Iterations: 2

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Iterations: 4

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Iterations: 8

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Iterations: 16

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Iterations: 64

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Materials

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Diffuse Specular Glossy Tinted Clear Mirror

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Shapes • Spheres • Cubes • Triangles • Triangle Meshes • OBJ • STL

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k-d tree

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Textures

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Examples

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How does this differ from other rendering techniques?

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OpenGL

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Also OpenGL

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Live Coding Demo