the edge buffer a data structure for easy silhouette rendering by john w buchanan and mario c sousa
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The edge buffer : A data structure for easy silhouette rendering by John W. Buchanan and Mario C. Sousa. Goal . Render edges within relatively low end PC apps obstacle: Z-buffer reading is expensive if it exists All polygons are processed

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the edge buffer a data structure for easy silhouette rendering by john w buchanan and mario c sousa

The edge buffer : A data structure for easy silhouette rendering by John W. Buchanan and Mario C. Sousa

slide2
Goal
  • Render edges within relatively low end PC apps
    • obstacle: Z-buffer reading is expensive if it exists
  • All polygons are processed
  • Artists can define edges in the model which must be displayed
edge buffer eb uses
Edge Buffer (EB) uses:
  • Closed polyhedral objects
  • Open polyhedral objects

There are times when the Artist MUST define edges in order to produce accurate results

eb method attributes
EB Method Attributes
  • Polygonal mesh stored in indexed vertex mesh representation
  • Front/back facing polygons determined
  • Buffer takes up little additional storage space
closed polyhedral objects

1

5

2

4

3

Closed polyhedral objects

V- Vertex #

F- Front

B- Back

Original Object

Edges passed during pre-polygonal set-up

slide6

1

5

2

4

3

Closed polyhedral objects

F bits have 1 added to them in the corresponding fields

slide7

1

5

2

4

3

Closed polyhedral objects

Adding 1 to the F bit twice results in a 0 representing a front-facing, absolute edge.

slide8

1

5

2

4

3

Closed polyhedral objects

Back-facing bits have 1’s added to them, the first silhouette is found.

slide9

1

5

2

4

3

Closed polyhedral objects

slide10

1

5

2

4

3

Closed polyhedral objects

slide11

1

5

2

4

3

Closed polyhedral objects

slide12

1

5

2

4

3

Closed polyhedral objects

Silhouettes are found and rendered

slide13

5

6

1

4

8

7

2

3

Open polyhedral objects

Original Open Object

Result of edge buffer technique on Open Objects

slide14

5

6

1

4

8

7

2

3

Open polyhedral objects

Original Object

Rendering edges which do not end in 00

slide15

5

6

1

4

8

7

2

3

Open polyhedral objects

Original object

Allow Artist to define edges to be rendered

determining back facing artist edges
Determining back-facing artist edges
  • Three new flags are added to bit field: A, F~ and B~.
    • Artist defined edge.
    • Front or Back Absolute.

--------->

slide17

RESULTS

A F B F~ B~

0 0 0 0 1

= Back-Facing Absolute Edge not to be rendered

11111

00010

10011

00001

11111

slide18

RESULTS

A F B F~ B~

0 0 0 1 0

= Front-Facing Absolute Edge not to be rendered

11111

00010

10011

00001

11111

slide19

RESULTS

A F B F~ B~

1 0 0 1 1

= Artist edge sharing vertices with both back-facing and front-facing polygons will be rendered

11111

00010

10011

00001

11111

slide20

RESULTS

A F B F~ B~

1 1 1 1 1

= Artist Edge sharing vertices with both back-facing and front-facing polygons will be rendered

11111

11111

00010

00010

10011

10011

00001

00001

11111

11111

slide21

RESULTS

A F B F~ B~

1 1 1 1 1

= Artist edge sharing vertices with both back-facing and front-facing polygons

11111

00010

10011

00001

11111

conclusions
Conclusions
  • Little additional storage space
    • At least two bits per edge.
  • Front-and back computations being done
  • Objects stored in indexed polygonal mesh representation
  • Artist Edge can be defined during pre-processing.
  • Increased computation adds less than 1% to rendering time
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