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Ray Tracing

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Photo-Realism

Created by David Derman – CISC 440

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Created by Jan Oberlaender – CISC 640

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Created by Jan Oberlaender – CISC 640

5Created by Donald Hyatt http://www.tjhsst.edu/~dhyatt/superap/povray.html

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RAY Tracing

Ray Tracing :

Ray tracing is a method for calculating the path of waves or particles through a system.

RAY

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Sun Ray

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Types of Rays

Ray tracing in Physics:

Which is used for analyzing optical and other systems.

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Types of Rays

Ray tracing Graphics :which is used for

3D image generation

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Ray tracing Graphics

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How it Works

Ray Tracing :technique use for

generating an 3-D image by Tracing the path of Light through Pixels in an Image Plane and simulating the effects of its encounters with virtual objects.

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Introduction

Ray Tracing based rendering method for generating realistic images on the computer.

In ray tracing, a ray of light is traced in a forward and backwards direction.

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Overview

Forward Ray tracing Rays from light source

bounce of objects before reaching the camera

Computational wastage

Backward Ray tracing Track only those rays

that finally made it to the camera

Courtesy: Angel

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Ray Tracing

We start from the eye or camera and trace the ray through a pixel in the image plane into the scene and determine what it intersects.

The pixel is then set to the color values returned by the ray.

If the ray misses all objects, then that pixel is shaded the background color.

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Ray Tracing

Sometimes a ray misses all objects

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Ray Tracing (contd.)

Sometimes a ray hits an object

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Ray Tracing (contd.)

Sometimes Ray intersect point`s and Reflect Back To Light Source.

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Ray Tracing (contd.)

Shadow rays intersect another objectFirst intersection point in shadow of the

second object

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Ray Tracing (contd.)

Reflected ray generated at point of intersection

Tested with all the objects in the scene

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Ray Tracing (contd.)

Local illumination model applied at the point of intersection

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Ray Tracing (contd.)

Transparent objectGenerate a transmitted ray and test against

all objects in the scene

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Effects Of Ray on Object

When Ray Hit the Surface of an Object it produce different effect`s.

Reflection.Refraction/Transmission.Shadow

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Reflection

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Reflection

Created by David Derman – CISC 440

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Reflection

Created by David Derman – CISC 440

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Reflection

Created by David Derman – CISC 440

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Reflection

Created by David Derman – CISC 440

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Refraction

Bending of light rays as it crosses interface between media having different refractive indices

Snell’s Law

c1,c2 – Refractive

index

2211 sinsin cc

Courtesy F.S. Hill, “Computer Graphics using OpenGL”

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Refraction

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Refraction

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Adding shadows

Shadow Feelers :

A shadow feeler is a ray sent from a point u on the surface of an object towards a light source to determine whether the light is visible from the point u or whether it is occluded by intervening objects.

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Shadow Feeler

If the shadow feeler hits an object before reaching the light, then the light is presumed to be occluded by the object so that the point is in a shadow.

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Shadow Effects

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Angle Dependent Reflection

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Angle Of incident

<180

<90

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Ray object intersection

Equation of a ray “S” is the starting point and “c” is the direction of the

ray, t is angle Given a surface in implicit form F(x,y,z)

plane: sphere: cylinder:

All points on the surface satisfy F(x,y,z)=0

ttr cS

1,, 222 zyxzyxF

101,, 22 zyxzyxF

ddczbyaxzyxF xn,,

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Ray Tracing Algorithm Begin tracing.

Construct a ray through each pixel in the scene. Pixel color = result of tracing the ray

Tracing the ray Find intersection of ray with closest object in the

scene. Compute intersection point and normal at the

intersection point. Shade the point.

Shade the point For each light…

Determine if point is in shadow relative to light source. Using illumination model, determine color at the intersection

point.

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Ray Tracing Algorithminteger i, j;

ray r; { defines starting point and direction of ray }

point eyePt, hitPt;shape pointer hitObjP;real array I [XMIN .. XMAX, YMIN .. YMAX];

for i:=YMIN to YMAX do

for j:=XMIN to XMAX do

begin

ComputeRay (i,j,r);FirstIntersection1 (r,hitPt,hitN,hitObjP);

if hitObjP π nil

then I[i,j] := Shade (eyePt,nil,hitPt,hitN,hitObjP,1)

else I[i,j] := background

end;procedure ComputeRay (integer i, j; ref ray r)

{Computes the ray r (in world coordinates) from the eye defined by the (i,j)th pixel} procedure FirstIntersection1 (ray r; ref point hitPt, hitN; ref shape pointer hitObjP)

{Returns a pointer hitObjP to the closest object intersected by the ray r, the point hitPt

on that object where the ray intersects it, and the surface normal hitN at that point.Use bounding boxes for projected objects in view plane to speed up computation} .