1 dr. scott schaefer hidden surfaces. 2/62 hidden surfaces
TRANSCRIPT
![Page 1: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/1.jpg)
1
Dr. Scott Schaefer
Hidden Surfaces
![Page 2: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/2.jpg)
2/62
Hidden Surfaces
![Page 3: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/3.jpg)
3/62
Hidden Surfaces
![Page 4: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/4.jpg)
4/62
Hidden Surfaces
![Page 5: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/5.jpg)
5/62
Backface Culling
![Page 6: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/6.jpg)
6/62
Backface Culling
view direction
v
![Page 7: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/7.jpg)
7/62
Backface Culling
view direction
n
v
![Page 8: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/8.jpg)
8/62
Backface Culling
view direction
n
v
0vn , draw polygon
![Page 9: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/9.jpg)
9/62
Backface Culling
view direction
n
v
0vn , cull polygon
![Page 10: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/10.jpg)
10/62
Backface Culling
![Page 11: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/11.jpg)
11/62
Backface Culling
1
2
3
counter clock-wise orientation, draw polygon
![Page 12: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/12.jpg)
12/62
Backface Culling
1
2
3
clock-wise orientation, cull polygon
![Page 13: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/13.jpg)
13/62
Backface Culling
Advantages Improves rendering speed by removing
roughly half of polygons from scan conversion
DisadvantagesAssumes closed surface with consistently
oriented polygonsNOT a true hidden surface algorithm!!!
![Page 14: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/14.jpg)
14/62
Backface Culling
Is this all we have to do?
![Page 15: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/15.jpg)
15/62
Backface Culling
Is this all we have to do? No!- Can still have 2 (or more) front faces that map to
the same screen pixel
![Page 16: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/16.jpg)
16/62
Backface Culling
Is this all we have to do? No!- Can still have 2 (or more) front faces that map to
the same screen pixel- Which actually gets drawn?
![Page 17: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/17.jpg)
17/62
Painter’s Algorithm
Sort polygons according to distance from viewer
Draw from back to front
How do we sort polygons?
![Page 18: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/18.jpg)
18/62
Painter’s Example
z = 0.7z = 0.3
z = 0.1
Sort by depth:Green rectRed circle
Blue triz = 0
![Page 19: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/19.jpg)
19/62
Painter’s Algorithm
![Page 20: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/20.jpg)
20/62
Sometimes there is NO ordering that produces correct results!!!
Painter’s Algorithm
![Page 21: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/21.jpg)
21/62
Painter’s Algorithm
1. Sort all objects’ zmin and zmax
![Page 22: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/22.jpg)
22/62
Painter’s Algorithm
1. Sort all objects’ zmin and zmax
2. If an object is uninterrupted (its zmin and zmax are adjacent in the sorted list), it is fine
![Page 23: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/23.jpg)
23/62
Painter’s Algorithm
1. Sort all objects’ zmin and zmax
2. If an object is uninterrupted (its zmin and zmax are adjacent in the sorted list), it is fine
3. If 2 objects DO overlap
3.1 Check if they overlap in x
- If not, they are fine
3.2 Check if they overlap in y
- If not, they are fine
- If yes, need to split one
![Page 24: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/24.jpg)
24/62
Painter’s Algorithm
The splitting step is the tough one - Need to find a plane to split one polygon by so
that each new polygon is entirely in front of or entirely behind the other
- Polygons may actually intersect, so then need to split each polygon by the other
![Page 25: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/25.jpg)
25/62
Painter’s Algorithm
The splitting step is the tough one - Need to find a plane to split one polygon by so
that each new polygon is entirely in front of or entirely behind the other
- Polygons may actually intersect, so then need to split each polygon by the other
After splitting, you can resort the list and should be fine
![Page 26: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/26.jpg)
26/62
Painter’s Algorithm-Summary
AdvantagesSimple algorithm for ordering polygons
DisadvantagesSorting criteria difficult to produceRedraws same pixel many timesSorting can also be expensive
![Page 27: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/27.jpg)
27/62
Depth (“Z”) Buffer
Simple modification to scan-conversion Maintain a separate buffer storing the closest
“z” value for each pixel Only draw pixel if depth value is closer than
stored “z” valueUpdate buffer with closest depth value
![Page 28: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/28.jpg)
28/62
Depth (“Z”) Buffer
AdvantagesSimple to implementAllows for a streaming approach to
polygon drawing Disadvantages
Requires extra storage spaceStill lots of overdraw
![Page 29: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/29.jpg)
29/62
Binary Space Partitioning Trees
BSP tree: organize all of space (hence partition) into a binary tree- Preprocess: overlay a binary tree on objects in the scene
- Runtime: correctly traversing this tree enumerates objects from back to front
- Idea: divide space recursively into half-spaces by choosing splitting planes
Splitting planes can be arbitrarily oriented
![Page 30: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/30.jpg)
30/62
BSP Trees: Objects
1 2 3
45
6 78
9
![Page 31: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/31.jpg)
31/62
BSP Trees: Objects
1 2 3
45
6 78
9
+
-
![Page 32: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/32.jpg)
32/62
BSP Trees: Objects
1 2 3
45
6 78
9
985 61 42 3
Put front objects in the left branch
7
+
--+
![Page 33: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/33.jpg)
33/62
BSP Trees: Objects
1 2 3
45
6 78
9
985 61 42 3
Put front objects in the left branch
7
-+
-+ -+
![Page 34: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/34.jpg)
34/62
BSP Trees: Objects
1 2 3
45
6 78
9
895 6
1
32 4
Put front objects in the left branch
7
-+
-+ -+
-+ -+ -+
![Page 35: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/35.jpg)
35/62
BSP Trees: Objects
1 2 3
45
6 78
9
865 6
1
32
2 4
Put front objects in the left branch
7 9
-+
-+ -+
+ + -+- -
+ - + -
![Page 36: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/36.jpg)
36/62
BSP Trees: Objects
1 2 3
45
6 78
9
865 6
1
32
2 4
Put front objects in the left branch
7 9
-+
-+ -+
+ + -+- -
+ - + -
When to stop the recursion?
![Page 37: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/37.jpg)
37/62
Object Splitting
No bunnies were harmed in my example But what if a splitting plane passes through
an object?- Split the object; give half to each node:
- Worst case: can create up to O(n3) objects!
Ouch
![Page 38: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/38.jpg)
38/62
Building a BSP Tree
Choose a splitting polygon Sort all other polygons as
Front Behind Crossing On
Add “front” polygons to front child, “behind” to back child
Split “crossing” polygons with infinite plane Add “on” polygons to root Recur
![Page 39: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/39.jpg)
39/62
Building a BSP Tree
1 2
3
4
5
6
7
![Page 40: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/40.jpg)
40/62
Building a BSP Tree
1 2
3
4
5
6
7
2,3,4,5,6,7
1
b
![Page 41: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/41.jpg)
41/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
3
7-2,6, 5-2
1
b
bf
2,4,5-1,7-1
![Page 42: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/42.jpg)
42/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2 4, 5-1
3
7-17-2,6, 5-2
1
b
b
b
f
f
![Page 43: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/43.jpg)
43/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2
5-1
3
7-1
47-2,6, 5-2
1
b
b
b
b
f
f
![Page 44: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/44.jpg)
44/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2
5-1
3
7-1
47-2,6, 5-2
1
b
b
b
b
f
f
![Page 45: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/45.jpg)
45/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2
5-1
3
7-1
47-2,6, 5-2
1
b
b
b
b
f
f
![Page 46: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/46.jpg)
46/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2
7-2
5-1
3
7-1
46, 5-2
1
b b
b
b
b
f
f
![Page 47: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/47.jpg)
47/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
5-2
2
7-2
5-1
3
7-1
46
1
b b
bb
b
b
f
f
![Page 48: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/48.jpg)
48/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2
7-2
5-1
3
7-1
46
1
b b
b
b
b
f
f
5-2
b
![Page 49: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/49.jpg)
49/62
2
7-2
Building a BSP Tree
1 2
3
4
6
5-1
3
7-1
46
1
7-2
7-1
5-2
5-1
b b
b
b
b
f
f
5-2
b
![Page 50: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/50.jpg)
50/62
Rendering with a BSP Tree
If eye is in front of plane Draw “back” polygons Draw “on” polygons Draw “front” polygons
If eye is behind plane Draw “front” polygons Draw “on” polygons Draw “back” polygons
Else eye is on plane Draw “front” polygons Draw “back” polygons
![Page 51: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/51.jpg)
51/62
BSP Trees: Objects
1 2 3
45
6 78
9
865 6
1
32
2 4
Correctly traversing this tree enumerates objects from back to front
7 9
-+
-+ -+
+ + -+- -
+ - + -
Traversal order?
![Page 52: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/52.jpg)
52/62
BSP Trees: Objects
1 2 3
45
6 78
9
865 6
1
32
2 4
Correctly traversing this tree enumerates objects from back to front
7 9
-+
-+ -+
+ + -+- -
+ - + -
Traversal order:8->9->7->6->5->3->4->2->1
![Page 53: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/53.jpg)
53/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
Traversal order: 2
7-2
5-1
3
7-1
46
1
b b
b
b
b
f
f
5-2
b
![Page 54: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/54.jpg)
54/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
Traversal order:6->(5-2)->(7-2)->3->(5-1)->4->(7-1)->2->1
2
7-2
5-1
3
7-1
46
1
b b
b
b
b
f
f
5-2
b
![Page 55: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/55.jpg)
55/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
Traversal order: 2
7-2
5-1
3
7-1
46
1
b b
b
b
b
f
f
5-2
b
![Page 56: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/56.jpg)
56/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
2
7-2
5-1
3
7-1
46
1
b b
b
b
b
f
f
5-2
bTraversal order:1->2->(7-1)->4->(5-1)->3->(7-2)->(5-2)->6
![Page 57: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/57.jpg)
57/62
Building a BSP Tree
1 2
3
4
6
7-2
7-1
5-2
5-1
Traversal order? 2
7-2
5-1
3
7-1
46
1
b b
b
b
b
f
f
5-2
b
![Page 58: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/58.jpg)
58/62
Rendering with a BSP Tree
Advantages No depth comparisons needed Polygons split and ordered automatically
Disadvantages Computationally intense preprocess stage
restricts algorithm to static scenes Splitting increases polygon count Redraws same pixel many times Choosing splitting plane not an exact science
![Page 59: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/59.jpg)
59/62
Improved BSP Rendering
Take advantage of view direction to cull away polygons behind viewer
![Page 60: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/60.jpg)
60/62
Improved BSP Rendering
Take advantage of view direction to cull away polygons behind viewer
View frustum
![Page 61: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/61.jpg)
61/62
Improved BSP Rendering
Take advantage of view direction to cull away polygons behind viewer
![Page 62: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/62.jpg)
62/62
OpenGL and Hidden Surfaces
glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glCullFace ( GL_BACK );
![Page 63: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/63.jpg)
63/62
![Page 64: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/64.jpg)
64/62
Scan Line Algorithm
Assume for each line of screen, we have scan-lines for all polygons intersecting that line
For each polygon, keep track of extents of scan line
Whenever the x-extents of two scan lines overlap, determine ordering of two polygons
![Page 65: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/65.jpg)
65/62
Scan Line Algorithm
![Page 66: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/66.jpg)
66/62
Scan Line Algorithm
![Page 67: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/67.jpg)
67/62
Scan Line Algorithm
![Page 68: 1 Dr. Scott Schaefer Hidden Surfaces. 2/62 Hidden Surfaces](https://reader036.vdocuments.mx/reader036/viewer/2022062313/56649d365503460f94a0d9d2/html5/thumbnails/68.jpg)
68/62
Scan Line Algorithm
AdvantagesTakes advantage of coherence resulting in
fast algorithmDoes not require as much storage as depth
buffer Disadvantages
More complex algorithmRequires all polygons sent to GPU before
drawing