COMPUTING
Lecture 9 - Ray tracing I

Lecture 9 - Ray tracing I - Interactive Computer Graphics...

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Interactive Computer Graphics: Lecture 9 Ray tracing
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Graphics Lecture 10: Slide 2
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Graphics Lecture 10: Slide 3
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Graphics Lecture 9: Slide 4 Direct and Global Illumination Direct illumination : A surface point receives light directly from all light sources in the scene. – Computed by the direct illumination model. Global illumination : A surface point receives light after the light rays interact with other objects in the scene. – Points may be in shadow. – Rays may refract through transparent material. – Computed by reflection and transmission rays.
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Graphics Lecture 9: Slide 5 Albrecht Dürer’s Ray Casting Machine Albrecht Dürer, 16th century Graphics Lecture 10: Slide 5
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Graphics Lecture 9: Slide 6 Arthur Appel, 1968 On calculating the illusion of reality, 1968 Cast one ray per pixel (ray casting). – For each intersection, trace one ray to the light to check for shadows – Only a local illumination model Developed for pen-plotters
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Graphics Lecture 9: Slide 7 Ray casting cast ray Intersect all objects color = ambient term For every light cast shadow ray col += local shading term
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Graphics Lecture 9: Slide 8 Ray casting
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Graphics Lecture 9: Slide 9 Turner Whitted, 1980 An Improved Illumination Model for Shaded Display, 1980 First global illumination model: – An object’s color is influenced by lights and other objects in the scene – Simulates specular reflection and refractive transmission
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Graphics Lecture 9: Slide 10 Turner Whitted, 1980
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Graphics Lecture 9: Slide 11 Recursive ray casting trace ray Intersect all objects color = ambient term For every light cast shadow ray col += local shading term If mirror col += k_refl * trace reflected ray If transparent col += k_trans * trace transmitted ray
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Graphics Lecture 9: Slide 12 Does it ever end? Stopping criteria: – Recursion depth: Stop after a number of bounces – Ray contribution: Stop if reflected / transmitted contribution becomes too small
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Graphics Lecture 9: Slide 13 Ray tracing: Primary rays For each ray we need to test which objects are intersecting the ray: – If the object has an intersection with the ray we calculate the distance between viewpoint and intersection – If the ray has more than one intersection, the smallest distance identifies the visible surface.
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  • Spring '14
  • Angle of Incidence, Total internal reflection, Geometrical optics, ray tracing

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