Ray TracingMike MerchantNicholas Hilbert

What is Ray Tracing?

Color•Image plane (pixels) are determined by

the color of the light ray that passes through that pixel. (Ultimately… determining the color of each pixel is the point of ray tracing)

Types of Ray Tracing - Forwards•Simulates real life (aka Photon Tracing)•Accurately determines color of each

object•Highly inefficient

Types of Ray Tracing - Backwards•Emits 1 ray from the viewer to each pixel

on the screen and tracks its path•No unnecessary rays for simple ray tracer

(1080p screen = 2,073,600 rays… not too bad)

•Still time consuming

Complexity is O(heightscreen *

widthscreen * numobjects)

REFLECTION + REFRACTIONREFLECTIONREFRACTION

Recursively Reflecting/Refracting Rays• Create a tree of rays: root note is the original ray, each node

is a reflected/refracted ray, and all leaves are non-reflected/non-refracted rays… go until a depth limit is reached or there are no more nodes

((Same complexity as before)number of reflected/refracted rays)

Current Overview

Problems •Time Consuming:

▫Impossible for real-time graphics▫Takes time to calculate closest object

through ray (usually involves the dreaded square root function)

•Aliasing•Image has perfect reflection (unnatural)

Anti-Aliasing •Ray tracing gives a color for all points on

image… but a square pixel contains an infinite number of points which might not all be the same color

•Shoot more rays at each pixel (random or not) then filter the result and color the pixel accordingly

Distributed Ray Tracing – Monte Carlo Ray Tracing•Light can bounce off in many directions at

one point•Can add real world effects, such as:

GlossSoft ShadowsFocus

Finished Overview• Complicated Ray Tracer is able to simulate an image in real life…

but must require lots of calculations

• Add more rays that intersect at a point (for distributed ray tracing)

Accelerated Ray Tracing•Adaptive depth control

▫Decrease the depth of possible recursion for reflected/refracted rays

•Only keep rays needed for basic image▫Remove features mentioned in the last few

slides•Bounding Volumes•“Embarrassingly parallel”

Bounding Volumes• Bind objects together into

bigger objects▫ If ray doesn’t hit bounded

object, it won’t hit objects inside either

▫ Also used for single objects

Embarrassingly parallel•Wikipedia: “… an embarrassingly parallel

workload, is one for which little or no effort is required to separate the problem into a number of parallel tasks”

•Only need scene and a ray to calculate pixel’s color

Finale•Questions?