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Clipping Polygons

This article explores why polygon clipping is difficult and covers the Sutherland-Hodgman algorithm for clipping polygons. It discusses possible outcomes, concave polygons, and the input/output of the algorithm.

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Clipping Polygons

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  1. Clipping Polygons Dr. Scott Schaefer

  2. Clipping Polygons

  3. Clipping Polygons

  4. Why Is Polygon Clipping Hard? • What happens to a triangle during clipping? - possible outcomes: triangle triangle triangle quad triangle 5-gon

  5. Why Is Polygon Clipping Hard? • What happens to a triangle during clipping? - possible outcomes: triangle triangle triangle quad triangle 5-gon How many sides could a clipped triangle have?

  6. How Many Sides? 7

  7. Why Is Polygon Clipping Hard? Concave polygon Multiple polygons

  8. Why Is Polygon Clipping Hard? • A really tough case

  9. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  10. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  11. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  12. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  13. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  14. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  15. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  16. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  17. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation

  18. Sutherland-Hodgman Clipping • Basic idea: - consider each edge of the view window individually - clip the polygon against the view window edge’s equation - after doing all edges, the polygon is fully clipped

  19. Sutherland-Hodgman Clipping • Input/output for algorithm: - input: list of polygon vertices in order {abcdef} a f b e d c

  20. Sutherland-Hodgman Clipping • Input/output for algorithm: - input: list of polygon vertices in order - output: list of clipped polygon vertices consisting of old vertices (maybe) and new vertices (maybe)

  21. outside inside outside inside S E E S I outputE output no output Sutherland-Hodgman Clipping • Edge from S to E takes one of four cases: outside inside outside inside E S E S E output I output

  22. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  23. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  24. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  25. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  26. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  27. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  28. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm b

  29. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  30. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  31. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  32. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  33. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  34. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  35. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  36. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  37. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  38. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  39. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  40. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  41. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  42. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  43. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  44. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  45. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  46. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  47. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  48. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  49. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

  50. Out In Out In Out In Out In Output I,E No output Output E Output I Sutherland-Hodgman Algorithm

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