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 PowerPoint PPT Presentation


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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

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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


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

  • 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


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

1

5

2

4

3

Closed polyhedral objects

F bits have 1 added to them in the corresponding fields


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

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.


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

1

5

2

4

3

Closed polyhedral objects

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


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

1

5

2

4

3

Closed polyhedral objects


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

1

5

2

4

3

Closed polyhedral objects


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

1

5

2

4

3

Closed polyhedral objects


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

1

5

2

4

3

Closed polyhedral objects

Silhouettes are found and rendered


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

5

6

1

4

8

7

2

3

Open polyhedral objects

Original Open Object

Result of edge buffer technique on Open Objects


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

5

6

1

4

8

7

2

3

Open polyhedral objects

Original Object

Rendering edges which do not end in 00


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

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.

--------->


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

RESULTS

A F B F~ B~

0 0 0 0 1

= Back-Facing Absolute Edge not to be rendered

11111

00010

10011

00001

11111


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

RESULTS

A F B F~ B~

0 0 0 1 0

= Front-Facing Absolute Edge not to be rendered

11111

00010

10011

00001

11111


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

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


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

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


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

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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