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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 2

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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 are 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) 4

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 5

 needs incident and viewing direction vector Bi-directional Reflectance Distribution Function 6

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9 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 dB leaving each surface point Summing the energy contributions over all surfaces

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15 Form Factor F jk 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)

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Ray Tracing Example Original scene description Ray Tracing Random Object InsertedRandom Light Source Inserted 20 Inverse Global Illumination[Paul Debevec] – SIGGRAPH ‘99