Ray Casting Surface intersection Visible surface detection Ray

• Ray Casting • Surface intersection • Visible surface detection • Ray Tracing • Bounce the ray • Collecting intensity • Technique for global reflection and transmission • • Visible-surface detection Shadow effects Transparency Multiple light-source illumination • Highly realistic vs. computation time

• Scene Description • Ray-path • From the center of projection, through the center of each screen-pixel position • Assign intensity accumulated along the ray to the pixel • Since there an infinite number of ray paths, we trace a light path backward from pixel to the scene. • One ray per pixel(like the scene through pinhole camera)

• Basic algorithm • Determine surface-intersection for each pixel ray • Identify visible surface • Repeated for secondary rays • Reflection, refraction rays • Ray-tracing tree • • Left branch : reflection Right branch : transmission Define maximum depth Terminate if it reaches the preset maximum or strikes a light source • Accumulate the intensity, starting at the bottom(terminal) • The sum of the attenuated intensities at the root node • If no surfaces are intersected, the pixel is assigned the intensity of the background

Bi-directional Reflectance Distribution Function needs incident and viewing direction vector

• The method for describing diffuse reflections • • Consider radiant energy transfers between surfaces Basic Radiosity Model • Consider the radiant-energy interactions between all surfaces in a scene Differential amount of radiant energy d. B leaving each surface point • Summing the energy contributions over all surfaces

• Form Factor Fjk • Consider energy transfer • From surface j to surface k • • , for all k(conservation of energy) , for all j(assuming only plane or convex surface patches)

Ray Tracing Example Inverse Global Illumination[Paul Debevec] – SIGGRAPH ‘ 99 Original scene description Ray Tracing Random Light Source Inserted Random Object Inserted