Page 59 - DCAP313_LAB_ON_COMPUTER_GRAPHICS

Unit 4: Implementing Circle Algorithm
Avinash Bhagat, Lovely Professional University

Unit 4: Implementing Circle Algorithm Notes

CONTENTS

Objectives
Introduction
4.1 Concept of Circle Algorithm
4.2 Midpoint Circle Drawing Algorithm
4.2.1 Implement Midpoint Algorithm
4.2.2 Implement Midpoint Circle Drawing Algorithm in C
4.2.3 Advantage and Disadvantage of Midpoints Circle Drawing Algorithm
4.3 Bresenham’s Circle Drawing Algorithm
4.3.1 Bresenham’s Circle Drawing Algorithm Using C Programming
4.4 Summary
4.5 Keywords
4.6 Review Questions
4.7 Further Readings

Objectives

After studying this unit, you will be able to:
• Understand the concept of circle algorithm
• Define the midpoint circle drawing algorithm

• Discuss the Bresenham’s circle drawing algorithm

Introduction

Critical to this definition is the detail that every simple closed curve declares a well-defined
interior; that follows from the Jordan Curve Theorem. All simple closed curves can be classified
as negatively oriented (clockwise), absolutely oriented (counterclockwise), or non-orient able. A
circle oriented counterclockwise is an example of a positively oriented curve. The same circle
oriented clockwise would be a negatively oriented curve.

The concept of orientation of a curve is just a particular case of the notion of orientation of a
manifold (that is, besides orientation of a curve one may also speak of orientation of a surface,
hyper surface, etc.). Here, the interior and the exterior of a curve both inherit the usual orientation
of the plane. The positive orientation on the curve is then the orientation it inherits as the
boundary of its interior; the negative orientation is inherited from the exterior. A line forming
a closed loop, every point on which is a fixed distance from a center point.

A circle is a type of line. Imagine a straight line segment that is bent around until its ends join.
Then arrange that loop until it is exactly circular - that is, all points along that line are the same
distance from a centre point. There is a difference between a circle and a disk. A circle is a line,
and so, for example, has no area - just as a line has no area. A disk however is a round portion
of a plane which has a circular outline. If you draw a circle on paper and cut it out, the round
piece is a disk.

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