Post on 17-Dec-2015
David Luebke 1/19/99
CS 551/651: CS 551/651: Advanced Computer GraphicsAdvanced Computer Graphics
David LuebkeDavid Luebke
cs551dl@cs.virginia.educs551dl@cs.virginia.edu
http://www.cs.virginia.edu/~cs551dlhttp://www.cs.virginia.edu/~cs551dl
David Luebke 1/19/99
AdministriviaAdministrivia
Hand out syllabusHand out syllabus– Instructor/TA coordinatesInstructor/TA coordinates– Topic listTopic list– PrereqsPrereqs– TextbookTextbook– AssignmentsAssignments– Grading & Honor CodeGrading & Honor Code
David Luebke 1/19/99
AdministriviaAdministrivia
Hand out bio sheetHand out bio sheet– Front: for me to calibrate the courseFront: for me to calibrate the course– Back: for me to get to know youBack: for me to get to know you
Realistically, you should probably Realistically, you should probably have 3’s and 4’s on the front sectionshave 3’s and 4’s on the front sections
David Luebke 1/19/99
Questions?Questions?
David Luebke 1/19/99
RealismRealism
What is not realistic about the What is not realistic about the following images?following images?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism?Realism?
David Luebke 1/19/99
Realism…Realism…
A big part of realism is realistic A big part of realism is realistic lightinglighting
Is OpenGL’s lighting model realistic?Is OpenGL’s lighting model realistic?– Empirical specular termEmpirical specular term– ““Ambient” termAmbient” term– No shadowsNo shadows– No surface interreflectionNo surface interreflection
Crude light-surface interaction model
Strictly local illumination model
David Luebke 1/19/99
Global IlluminationGlobal Illumination
Realistic lighting is Realistic lighting is globalglobal, not local, not local– Surfaces shadow each otherSurfaces shadow each other– Surfaces illuminate each otherSurfaces illuminate each other
So realistic graphics = So realistic graphics = simulationsimulation Two long-time approachesTwo long-time approaches
– Ray-tracing: simulate light-ray opticsRay-tracing: simulate light-ray optics– Radiosity: simulate physics of light Radiosity: simulate physics of light
transfertransfer
David Luebke 1/19/99
Ray TracingRay Tracing
Powerful, elegant idea that unified:Powerful, elegant idea that unified:– Hidden surface determinationHidden surface determination– ShadowsShadows– Reflective surfacesReflective surfaces
Read Chapter 8 Read Chapter 8 (Browse 8.3.1-8.3.6)(Browse 8.3.1-8.3.6)
David Luebke 1/19/99
Ray Tracing OverviewRay Tracing Overview
To determine visible surfaces at To determine visible surfaces at each pixel:each pixel:– Cast a ray from the eyepoint through Cast a ray from the eyepoint through
the center of the pixelthe center of the pixel– Intersect the ray with all objects in the Intersect the ray with all objects in the
scenescene– Whatever it hits first is the visible objectWhatever it hits first is the visible object
This is called This is called ray castingray casting
David Luebke 1/19/99
Ray CastingRay Casting
An example:An example:
ScreenEyepoint Scene
David Luebke 1/19/99
Recursive Ray TracingRecursive Ray Tracing
Obvious extension: Obvious extension: – Spawn additional rays off reflective Spawn additional rays off reflective
surfacessurfaces– Spawn transmitted rays through Spawn transmitted rays through
transparent surfacestransparent surfaces Leads to Leads to recursiverecursive
ray tracingray tracing
Primary Ray
Secondary Rays
David Luebke 1/19/99
Recursive Ray TracingRecursive Ray Tracing
Slightly less obvious extension:Slightly less obvious extension:– Trace a ray from point of intersection to Trace a ray from point of intersection to
light sourcelight source– If ray hits anything before light source, If ray hits anything before light source,
object is in shadowobject is in shadow– These are called These are called shadow raysshadow rays
David Luebke 1/19/99
Ray Tracing OverviewRay Tracing Overview
Ray tracing is simpleRay tracing is simple– No clipping, perspective projection No clipping, perspective projection
matrices, scan conversion of polygonsmatrices, scan conversion of polygons Ray tracing is powerfulRay tracing is powerful
– Reflection, refraction, shadowsReflection, refraction, shadows
David Luebke 1/19/99
Ray Tracing OverviewRay Tracing Overview
So why don’t we use ray tracing for So why don’t we use ray tracing for all our computer graphics needs?all our computer graphics needs?
Ray tracing is Ray tracing is slowslow– Complexity proportional to # of pixelsComplexity proportional to # of pixels– Typical screen ~ 1,000,000 pixelsTypical screen ~ 1,000,000 pixels– Typical scene « 1,000,000 polygonsTypical scene « 1,000,000 polygons
David Luebke 1/19/99
Where We’re GoingWhere We’re Going
Next 2-3 lectures: Basic ray tracingNext 2-3 lectures: Basic ray tracing– Casting primary rays, intersection Casting primary rays, intersection
tests, speedup techniques, etc.tests, speedup techniques, etc.– Exercise 1Exercise 1: RSRT: RSRT
2-3 lecture digression: Antialiasing2-3 lecture digression: Antialiasing– Signal theory, sampling, A-buffer, etc.Signal theory, sampling, A-buffer, etc.– Assignment 1Assignment 1: Sampling strategies: Sampling strategies
1-2 lectures: advanced ray tracing1-2 lectures: advanced ray tracing