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Lecture 8 Advanced Rendering Ray Tracing, Radiosity NPR

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Lecture 8 Advanced Rendering Ray Tracing, Radiosity NPR

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    1. Lecture 8 Advanced Rendering – Ray Tracing, Radiosity & NPR

    2. Ray Tracing

    3. Ray-Tracing Pseudocode For each ray r from eye to pixel, color the pixel the value returned by ray_cast(r):

    4. Pseudocode Explained s ? nearest_intersected_surface(r); Use geometric searching to find the nearest surface s intersected by the ray r p ? point_of_intersection(r, s); Compute p, the point of intersection of ray r with surface s u? reflect(r, s, p); v? refract(r, s, p); Compute the reflected ray u and the refracted ray v using Snell’s Laws Recall that the exact geometric-searching problem considered here was covered in last week’s lecture. Same goes for the intersection calculation, though only for spheres.Recall that the exact geometric-searching problem considered here was covered in last week’s lecture. Same goes for the intersection calculation, though only for spheres.

    5. Reflected and Refracted Rays Reflected and refracted rays are computed using Snell’s Law

    6. Pseudocode Explained phong(p, s, r) Evaluate the Phong reflection model for the ray r at point p on surface s, taking shadowing into account (see next slide) s.kreflect ? ray_cast(u) Multiply the contribution from the reflected ray u by the specular-reflection coefficient kreflect for surface s s.krefract ? ray_cast(v) Multiply the contribution from the refracted ray v by the specular-refraction coefficient krefract for surface s

    7. About Those Calls to ray_cast()... The function ray_cast() calls itself recursively There is a potential for infinite recursion Consider a “hall of mirrors” Solution: limit the depth of recursion A typical limit is five calls deep Note that the deeper the recursion, the less the ray’s contribution to the image, so limiting the depth of recursion does not affect the final image much

    8. Pros and Cons of Ray Tracing Advantages of ray tracing All the advantages of the Phong model Also handles shadows, reflection, and refraction Disadvantages of ray tracing Computational expense No diffuse inter-reflection between surfaces Not physically accurate Other techniques exist to handle these shortcomings, at even greater expense!

    9. An Aside on Antialiasing Our simple ray tracer produces images with noticeable “jaggies” Jaggies and other unwanted artifacts can be eliminated by antialiasing: Cast multiple rays through each image pixel Color the pixel the average ray contribution An easy solution, but it increases the number of rays, and hence computation time, by an order of magnitude or more

    10. Reflections Mathematically, what does this mean?

    11. Glossy Reflections We need to integrate the color over the reflected cone. Weighted by the reflection coefficient in that direction.

    12. Translucency Likewise, for blurred refractions, we need to integrate around the refracted angle.

    13. Translucency

    14. Translucency

    15. Shadows Ray tracing casts shadow feelers to a point light source. Many light sources are illuminated over a finite area. The shadows between these are substantially different. Area light sources cast soft shadows Penumbra Umbra

    16. Soft Shadows

    17. Soft Shadows

    18. Camera Models Up to now, we have used a pinhole camera model. These has everything in focus throughout the scene. The eye and most cameras have a larger lens or aperature.

    20. Motion Blur

    21. Supersampling

    22. More On Ray-Tracing Already discussed recursive ray-tracing! Improvements to ray-tracing! Area sampling variations to address aliasing Cone tracing (only talk about this) Beam tracing Pencil tracing Distributed ray-tracing!

    23. Area Subdivision (Warnock) (mixed object/image space)

    24. Area Subdivision (Warnock) Initialize the area to be the image plane Four cases: No polygons in area: done One polygon in area: draw it Pixel sized area: draw closest polygon Front polygon covers area: draw it Otherwise, subdivide and recurse

    25. BSP (Binary Space Partition) Trees

    26. BSP Trees

    27. BSP Trees

    28. BSP Trees

    29. Portals

    30. Portals

    31. More spatial subdivision methods… Octree Bounding volume (box, sphere) Oriented Bounding Box

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