David Luebke1/19/99 CS 551/651: Advanced Computer Graphics David Luebke

David Luebke1/19/99 Administrivia Hand out syllabus Hand out syllabus –Instructor/TA coordinates –Topic list –Prereqs –Textbook –Assignments –Grading & Honor Code

David Luebke1/19/99 Administrivia Hand out bio sheet Hand out bio sheet –Front: for me to calibrate the course –Back: for me to get to know you Realistically, you should probably have 3’s and 4’s on the front sections Realistically, you should probably have 3’s and 4’s on the front sections

David Luebke1/19/99 Questions?

Realism What is not realistic about the following images? What is not realistic about the following images?

David Luebke1/19/99 Realism?

Realism?

Realism?

Realism?

Realism?

Realism?

Realism?

Realism?

Realism… A big part of realism is realistic lighting A big part of realism is realistic lighting Is OpenGL’s lighting model realistic? Is OpenGL’s lighting model realistic? –Empirical specular term –“Ambient” term –No shadows –No surface interreflection Crude light-surface interaction model Strictly local illumination model

David Luebke1/19/99 Global Illumination Realistic lighting is global, not local Realistic lighting is global, not local –Surfaces shadow each other –Surfaces illuminate each other So realistic graphics = simulation So realistic graphics = simulation Two long-time approaches Two long-time approaches –Ray-tracing: simulate light-ray optics –Radiosity: simulate physics of light transfer

David Luebke1/19/99 Ray Tracing Powerful, elegant idea that unified: Powerful, elegant idea that unified: –Hidden surface determination –Shadows –Reflective surfaces Read Chapter 8 (Browse ) Read Chapter 8 (Browse )

David Luebke1/19/99 Ray Tracing Overview To determine visible surfaces at each pixel: To determine visible surfaces at each pixel: –Cast a ray from the eyepoint through the center of the pixel –Intersect the ray with all objects in the scene –Whatever it hits first is the visible object This is called ray casting This is called ray casting

David Luebke1/19/99 Ray Casting An example: An example: ScreenEyepointScene

David Luebke1/19/99 Recursive Ray Tracing Obvious extension: Obvious extension: –Spawn additional rays off reflective surfaces –Spawn transmitted rays through transparent surfaces Leads to recursive ray tracing Leads to recursive ray tracing Primary Ray Secondary Rays

David Luebke1/19/99 Recursive Ray Tracing Slightly less obvious extension: Slightly less obvious extension: –Trace a ray from point of intersection to light source –If ray hits anything before light source, object is in shadow –These are called shadow rays

David Luebke1/19/99 Ray Tracing Overview Ray tracing is simple Ray tracing is simple –No clipping, perspective projection matrices, scan conversion of polygons Ray tracing is powerful Ray tracing is powerful –Reflection, refraction, shadows

David Luebke1/19/99 Ray Tracing Overview So why don’t we use ray tracing for all our computer graphics needs? So why don’t we use ray tracing for all our computer graphics needs? Ray tracing is slow Ray tracing is slow –Complexity proportional to # of pixels –Typical screen ~ 1,000,000 pixels –Typical scene « 1,000,000 polygons

David Luebke1/19/99 Where We’re Going Next 2-3 lectures: Basic ray tracing Next 2-3 lectures: Basic ray tracing –Casting primary rays, intersection tests, speedup techniques, etc. –Exercise 1: RSRT 2-3 lecture digression: Antialiasing 2-3 lecture digression: Antialiasing –Signal theory, sampling, A-buffer, etc. –Assignment 1: Sampling strategies 1-2 lectures: advanced ray tracing 1-2 lectures: advanced ray tracing