Clipping and Hidden Surfaces Clipping Basic Line Clipping Cohen ...

Building Example
Building Example
• We will build a BSP
tree, in 2D, for a 3
room building
– Ignoring doors
• Splitting edge order
is shown
– “Back” side of edge
is side with the
number
5
2
3 4
1
6
1
- +
3a, 4a, 6 2, 3b, 4b, 5
3b
3a
5
2
1
6
4b
4a
31
32
Building Example
Building Example
1
- +
5b
5a
1
- +
5b
5a
3a, 4a, 6
2
- +
4b, 5a 3b, 5b
3b
2
4b
3a
+
4a, 6
-
4b, 5a
2
+
3b
+
3b
2
4b
3a
1
4a
5b
3a
1
4a
6
6
33
34
Building Example (Done)
BSP-Tree Rendering
3a
+
4a
1
- +
6
+
4b
-
2
+
3b
+ +
5a
5b
3b
3a
5b
1
6
2
5a
4b
4a
• Observation: Things on the opposite side of a splitting plane from
the viewpoint cannot obscure things on the same side as the
viewpoint
• Rendering algorithm is recursive descent of the BSP Tree
• At each node (for back to front rendering):
– Recurse down the side of the sub-tree that does not contain the viewpoint
Test viewpoint against the split plane to decide which tree
– Draw the polygon in the splitting plane
Paint over whatever has already been drawn
– Recurse down the side of the tree containing the viewpoint
35
36
6