Page 40 - DCAP313_LAB_ON_COMPUTER_GRAPHICS

Lab on Computer Graphics Avinash Bhagat, Lovely Professional University

Notes Unit 3: Implementing Line Algorithm

CONTENTS

Objectives
Introduction
3.1 Concept of Implementing Line Algorithm
3.2 Concept of Bresenham’s Algorithm
3.2.1 Bresenham’s Algorithm
3.2.2 The Integer Bresenham’s Algorithm
3.2.3 Bresenham’s Algorithm for Lines with Arbitrary Endpoints
3.2.4 Specifying the Driving Axis

3.2.5 C Code Line Drawing Algorithm
3.3 DDA Line Algorithm
3.3.1 Line DDA Algorithm
3.3.2 C Code DDA Line Algorithm
3.4 Summary
3.5 Keywords
3.6 Review Questions

3.7 Further Readings
Objectives

After studying this unit, you will be able to:
• Discuss the concept of implementing line algorithm
• Explain the concept of Bresenham’s algorithm

• Define the DDA line algorithm

Introduction

Line drawing is our first endeavor into the area of scan conversion. The need for scan conversion,
techniques is a direct result of scanning nature of raster displays (thus the names). Vector displays
are mainly well suited for the display of lines. All that is needed on a vector display to generate
a line is to supply the appropriate control voltages to the x and y deflection circuitry, and the
electron beam would traverse the line illuminating the desired segment. The only inaccuracies
in the lines drawn a vector display resulted from various non-line arties, such as quantization
and amplifier saturation, and the various noise sources in the display circuitry. When raster
displays came along the process of drawing lines became more difficult. Luckily, raster display
pioneers could benefit from previous work done in the area of digital plotter algorithms. A
pen-plotter is a hardcopy device used primarily to display engineering line drawings. Digital
plotters, like raster displays, are discretely addressable devices, where position of the pen on a
plotter is controlled by special motors called stepper motors that are connected to mechanical
linkages that translate the motor’s rotation into a linear translation. Stepper motors can precisely
turn a fraction of a rotation (for example 2 degrees) when the proper controlling voltages are

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