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Image Buffersand

Scan Conversion

CS-184: Computer Graphics

Prof. James O’Brien

Overview

� The frame buffer� Continuous versus discrete representations� Straight lines� Curves� Filled Polygons� Filling Algorithms

Image Buffers

� Chunk of memory to hold an image� Image made of pixels (finite area!)� Pixels have variable semantics

– RGB, gray-scale, depth, others...

� May be mapped to special hardware

Frame Buffer

Efficiency Issues

� Nice OO code helps avoid bugs� Indexing can be expensive� Out of order access may cause excess paging� Hardware often requires odd mappings

Continuous versus Discrete

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Continuous versus Discrete Continuous versus Discrete

� Pixels have finite size� Approximate desired locations

Straight Lines Straight Lines

Straight Lines

Note: Simplified version of algorithm... see text.

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Straight Lines

� Bresenham method much faster than DDE� Does not suffer from float problems

� Can do similar for other primitives

Curves

Approximate curves with line segments

Filled Polygons Filled Polygons

Filled Polygons Filled Polygons

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Filled Polygons Filled Polygons

Filled Polygons Filled Polygons

Filled Polygons

� Implement with

– Test in scanning code

– Tagging edges

– Adjusting vertex locations ( why a good option? )

– Others...

Filled Polygons

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Filled Polygons Filled Polygons

Filled Polygons

Self-intersecting polygons

A polygon

Result from non-zero winding number test

Result from parity test

Flood Fill (paint bucket)

� Fill in pixels inside some boundary

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Neighbors and Spans