Other%20Rendering%20Techniques

1
Other Rendering Techniques

• Types of rendering
• Wireframe techniques
• Scan-line conversion
• Reyes rendering
• Ray tracing (done)
• Shadows
• Reflections
• Depth of field, focus, etc.
• Antialiasing

2
Line only techniques

• Hidden-line removal
• Line graphics
• Wireframe images
• Halo line images

3
Floating Horizon Algorithms
4
Roberts Algorithm

• First visible line algorithm
• O(N2) complexity
• All objects must be convex volumes
• Excessively complex

5
Warnock Algorithm

• Spatial subdivision
• Quad-trees

6
Appels Algorithm

• Quantitative invisibility
• When a line goes behind something, increment by 1
• When it comes out, increment by -1

7
Haloed Lines
8
So much for wireframe
9
What are the ways to convert primitives to image?

• Scan-line conversion
• Ray tracing

Anything else?
10
Scan-line conversion

• Each primitive is mapped to 2D and then converted
  to image
• List priority algorithms
• Z-buffer techniques
• A-buffer techniques

11
Painters Algorithm

• Sort back to front
• Draw back to front
• Thats all there is to it
• Does this always work?

12
Z-buffer algorithms

• Associate a z value with each pixel
• Contains z for nearest point drawn so far
• OpenGL, Direct3D, etc.
• Where do we get the Z?

13
A-Buffer Algorithms

• Create a list of polygons for each scan line
• Determine x extents for each line
• Sort in z order
• Draw pixel for nearest line

14
Spanning Scan Line Algorithms

• Create a list of polygons for each scan line
• Determine x extents for each line
• Determine spans
• All end points and intersections partition spans
• Draw front line for each span

15
List priority algorithms

• Sort things in depth order
• Painters algorithm paints back to front
• We could just paint front if no overlaps
• Newell-Newell-Sancha Algorithm
• Provides way to sort polygons
• Splits any polygons if there is a cyclical
  relationship

16
Doing things in a z-buffer world

• Z-buffer the most common scan-line method
• Whats good about it?
• Whats bad about it?

17
Shadows?

• Why does OpenGL not show shadows?

18
Drawing Shadows

• Assume a light at (0,0,0). We want to know were
  the shadow projects on a plane defined by
  axbyczd0
• An occluding point S(sx,sy,sz,1)
• Anything along line through S would be
  (asx,asy,asz,1)
• Line intersection with plane is
• aasxabsyacszd0
• a-d/(asxbsycsz)
• Intersection with plane is -d(sx,sy,sz)/(asxbsy
  csz)

19
Using this equation
Similar approach exists For lights at infinity

• -d(sx,sy,sz)/(asxbsycsz)

1. Translate so light is at origin 2. Put this
matrix on stack (using translated plane) 3. Draw
object we are casting shadow of in shadow color
???
20
How I got this working

• I display the shadow into the stencil buffer
• I then draw the polygon with alpha value that
  decreases brightness
• See example program

21
Shadow Direction
Image from light 0 viewpoint
Image from light 1 viewpoint
What all can we do with this?
22
Lit Polygon Determination
Image from light 0 viewpoint
Image from light 1 viewpoint
Partition polygons into lit/not lit
sets Subdivide any that are partially lit
23
Shadow Texture
Image from light 0 viewpoint
Image from light 1 viewpoint
Create a texture map for each visible polygon
24
Shadow Map
Image from light 0 viewpoint
Depth map from light 0 viewpoint
The map partitions the space into shadowed/not
shadowed. For each point, determine which
partition we are in
25
Deep Shadow Maps
3D texture where each point is how much
illumination we receive
26
Shadow Volumes

• Polygons cast polyhedra of shadow volumes
• Intersect polyhedra and object space

27
Reflections/Transparency?

• How?

28
Environment Maps

• Uses vertex normals to generate texture
  coordinates
• How can we use this to generate
• Reflections
• Transparency with refraction?

29
Depth of Field?

• What?
• Why?
• How?

30
Motion Blur

• What?
• Why?
• How?