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Realistic Rendering

Realistic Rendering. Pavel Zemčík Department of Computer Science and Engineering, Faculty of Electrical Engineering and Computer Science, Technical University of Brno, Czech Republic zemcik@dcse.fee.vutbr.cz. What is realistic rendering?.

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Realistic Rendering

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  1. Realistic Rendering Pavel Zemčík Department of Computer Science and Engineering, Faculty of Electrical Engineering and Computer Science, Technical University of Brno, Czech Republic zemcik@dcse.fee.vutbr.cz

  2. What is realistic rendering? • Realistic (photo-realistic) rendering is the process of production of photograph-like images from a 3D model • Measure of “realism” is human • Affected by wide range of factors

  3. The realistic rendering needs • Models of objects, environment, and light • Light features (particle and wave effects) • Fine structure of objects’ surface • The material features (e.g. for glass)

  4. Is realistic rendering possible? NO!!! True realism is not possible • Accurate models not available • Light features impossible to model • Any close approximation very demanding • Very rough approximations used

  5. Rough realistic rendering The approximations usually assume • empty space between objects • no particle or wave light effects • simple scene geometry and lights • simple materials and surfaces

  6. Models of 3D scenes

  7. Constructive Solid Geometry • Constructive Solid Geometry (CSG) is a method for representing the 3D objects • tree structure (binary or n-ary) • primitive objects in the leaves • CSG (set) operations in other nodes

  8. CSG - example

  9. CSG operations • CSG operations are generally set operations on 3D objects’ volumes • unary operation  (not) • binary operations  (intersection, and) (union, or) \ (difference) • operations can be extended to n-ary

  10. CSG surface exclusion • CSG objects sometimes do not include the surface (for mathematical purity) • In such case, e.g. CSG union can be defined as:

  11. CSG - 3D example

  12. CSG - 3D rendered example

  13. CSG - 3D simple example

  14. CSG - 3D fractal example

  15. CSG - 3D glass example

  16. CSG - 3D complex example

  17. Rendering methods - objects • The objects are processed in a sequence • No objects interaction - no shadows

  18. Rendering methods - pixels • The pixels are processed in a sequence • No global interaction - no half-shadows

  19. Rendering methods - scene • The complete scene is processed • Very complex - no sharp shadows

  20. Rendering methods comparison

  21. Radiosity principle • Get form factors • Assign lights • Solve equation • Render usinga pixel method

  22. Ray tracing principle • The image is created by evaluation of content of each of the picture elements Durer A.: The Art of Measurement, Volume IV, The Netherlands, 1538

  23. Ray tracing algorithm For each pixel • send a ray eye  pixel  scene • calculate what can be seen • calculate the value of the pixel - • if necessary, proceed recursively

  24. Ray tracing - secondary rays • Secondary rays are necessary for evaluation of shadows and mirrors

  25. Sending a ray • Simple task, involves 3D projective transformation

  26. Geometry - what can be seen • Very complex task, in naive approach it involves calculation of intersection of the ray with all objects in the scene • (intersection often involves quadratic equation solution, or similar task) Estimated complexity: (P+S)*N e.g. (256x256+3*256x256)*1024=256M

  27. Calculation of pixel value • Depends on the local light model • Basic models include e.g. • flat model • diffusion • Phong model • mirror

  28. Geometry - sphere

  29. Geometry - sphere equations • Definition • Intersection (note that |d|=1) • or • Normal vector

  30. Geometry - halfspace

  31. Geometry - halfspace equations • Definition (note that p·n is constant) • Intersection • Normal vector (already in definition)

  32. Geometry - cylinder

  33. Geometry - cylinder equations • Definition • Intersection (substitution l=s-p, |d|=1) • Normal vector (intersection reused)

  34. Geometry - Quadric equations • Definition • Intersection (d’, s’ are d, s in 4D) • Normal

  35. Geometry - CSG

  36. Geometry - CSG algorithm • Shoot a ray & Convert sets to intervals • Apply CSG operations to intervals • or Convert to simpler list operations • Get the “real” intersection

  37. References • Gouraud H: Continouous Shading of Curved Surfaces, IEEE Transactions on Computer Graphics, n. 6, vol. C-20, june 1971, USA, pp. 623-629 • Foley J D, Van Dam A: Fundamentals of Interactive Computer Graphics, Addison-Wesley 1983, USA • Goral C M, Torrance K E, Greenberg D P, Battaile B: Modelling The Interaction of Light Between Diffuse Surfaces, sborník SIGGRAPH '84, ACM Computer Graphics, USA, 1984 • Watt A, Watt M: Advanced Animation and Rendering Techniques, Addison-Wesley 1992, USA, str. 33-64

  38. The end

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