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Computer Graphics

Computer Graphics. Lecture 07 Fasih ur Rehman. Last Class. Human Visual System Illusions Ray Tracing. Today’s Agenda. Human Visual System Illusions Ray Tracing. Ray Tracing. Building an imaging model by following light from a source is known as Ray Tracing

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Computer Graphics

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  1. Computer Graphics Lecture 07 FasihurRehman

  2. Last Class • Human Visual System • Illusions • Ray Tracing

  3. Today’s Agenda • Human Visual System • Illusions • Ray Tracing

  4. Ray Tracing • Building an imaging model by following light from a source is known as Ray Tracing • A Ray is a semi infinite line that emerges from s source and continues to infinity in one direction • Part of ray contributes in making image. • Surfaces • Diffusing • Reflecting • Refracting

  5. Ray Tracing • For each pixel intensity must be computed • Contributions of all rays must be taken into account • A ray when intercepted by a surface splits into two rays • Absorbed • Reflected

  6. Ray Intersections • Tracing a single ray requires determining if that ray intersects any one of potentially millions of primitives • This is the basic problem of ray intersection • Many algorithms exist to make this not only feasible, but remarkably efficient • Tracing one ray is a complex problem and requires serious work to make it run at an acceptable speed • Of course, the big problem is the fact that one needs to trace lots of rays to generate a high quality image

  7. Lighting • Once we have the key intersection information (position, normal, color, texture coordinates, etc.) we can apply any lighting model we want • This can include procedural shaders, lighting computations, texture lookups, texture combining, bump mapping, and more • Many of the most interesting forms of lighting involve spawning off additional rays and tracing them recursively • The result of the lighting equation is a color, which is used to color the pixel

  8. Ray Tracing Algorithm • Ray generation, which computes the origin and direction of each pixel’s viewing ray based on the camera geometry • Ray intersection, which finds the closest object intersecting the viewing ray • Shading, which computes the pixel color based on the results of ray intersection.

  9. Ray Tracing Algorithm • Structure of a ray tracing algorithm is • For each pixel do • compute viewing ray • find first object hit by ray and its surface normal ‘n’ • set pixel color to value computed from hit point, light, and n • End

  10. Summary

  11. References • Fundamentals of Computer Graphics Third Edition by Peter Shirley and Steve Marschner • Interactive Computer Graphics, A Top-down Approach with OpenGL (Third Edition) by Edward Angel.

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