1. Clipping Polygons
Lecture 31
Fri, Nov 9, 2007

2. Clipping Polygons
Clipping polygons requires that their edges be clipping by the line-clipping algorithm, and then new edges be created.
Keep in mind that OpenGL treats all polygons as though they were convex.
How does this make clipping more efficient?

3. Clipping Polygons
Clip region
Polygon

4. Clipping Polygons
Clip the top edge.

5. Clipping Polygons
Clip the top edge.

6. Clipping Polygons
Clip the top edge.

7. Clipping Polygons
Clip the right edge.

8. Clipping Polygons
Clip the right edge.

9. Clipping Polygons
Clip the right edge.

10. Clipping Polygons
Clip the bottom edge.

11. Clipping Polygons
Clip the bottom edge.

12. Clipping Polygons
Clip the bottom edge.

13. Clipping Polygons
Clip the left edge.

14. Clipping Polygons
Clip the left edge.

15. Clipping Polygons
Clip the left edge.

16. Clipping Polygons
The clipped polygon.

17. Clipping Polygons
When an edge is clipped, a shade and a normal are assigned to the new vertex by interpolating between the endpoints.
These interpolated shades and normals are used when the interior of the polygon is shaded.

18. Interpolating the Clipped Polygon
[1, 1, 0]
(2, 4) 3
(-6, 0)
[1, 0, 0]
[0, 1, 0]
(5, -2)
(-5, -2)
[0, 0, 1] -3 -4 4

19. Interpolating the Clipped Polygon
[1, 1, 0]
(2, 4) 3
(-6, 0)
[1, 0, 0]
[0, 1, 0]
(5, -2)
(-5, -2)
[0, 0, 1] -3 -4 4

20. Interpolating the Clipped Polygon
[1, 1, 0]
(2, 4) 3
(-6, 0)
[1, 0, 0]
[0, 1, 0]
(5, -2)
(-5, -2)
[0, 0, 1] -3 -4 4

21. Interpolating the Clipped Polygon
[1, 1, 0]
(2, 4)
(0, 3) 3
(-4, 1)
(-6, 0)
(4, 0)
[1, 0, 0]
[0, 1, 0]
(5, -2)
(-5, -2)
(-4, -2)
(4, -2)
[0, 0, 1] -3 -4 4

22. Interpolating the Clipped Polygon
[1, 1, 0]
[1, 0.75, 0]
(2, 4)
(0, 3) 3
[1, 0.25, 0]
(-4, 1)
[0.33, 1, 0]
(-6, 0)
(4, 0)
[1, 0, 0]
[0, 1, 0]
(5, -2)
(-5, -2)
(-4, -2)
[0, 0.1, 0.9]
(4, -2)
[0, 0, 1] -3
[0, 0.9, 0.1] -4 4

23. Interpolating the Clipped Polygon
[1, 0.75, 0]
[0.83, 1, 0]
(0, 3)
(2.5, 3) 3
[1, 0.25, 0]
(-4, 1)
[0.33, 1, 0]
(4, 0)
(-4, -2)
[0, 0.1, 0.9]
(4, -2) -3
[0, 0.9, 0.1] -4 4

24. Interpolating the Clipped Polygon
[1, 0.75, 0]
[0.83, 1, 0]
(0, 3)
(2.5, 3) 3
[1, 0.25, 0]
(-4, 1)
[0.33, 1, 0]
(4, 0)
(-4, -2)
[0, 0.1, 0.9]
(4, -2) -3
[0, 0.9, 0.1] -4 4