Page 150 - DCAP504_Computer Graphics

Pawan Kumar, Lovely Professional University Unit 10: Clipping II

Unit 10: Clipping II

CONTENTS
Objectives
Introduction

10.1 Polygon Clipping
10.2 Projection
10.3 Summary
10.4 Keywords
10.5 Self Assessment
10.6 Review Questions

10.7 Further Readings
Objectives

After studying this unit, you will be able to:
• Explain polygon clipping

• Discuss projections
Introduction
The projection is transforming of points and lines from one plane to the other plane. The projections are
done by connecting the corresponding points on two planes.

In projection it is important to control:
Did you know?
1. Projection type that can be perspective or orthographic.
2. Field of view and aspect ratio of image.

3. Near and far clipping panes.

In this unit, you will learn the third most common types of clipping, that is, polygon clipping. You will
learn various clipping algorithms that are developed for extracting a part of a defined scene for
viewing, displaying multi-window environment, drawing, painting, and so on. At the end of this unit
you will learn about projection, which helps transform 3-dimensional (3-D) objects on to a 2-
dimensional (2-D) projection plane. The projection is considered as the solution to the mismatch
between 3-D objects and 2-D displays.
10.1 Polygon Clipping
A polygon comprises a set of lines. A polygon is formed by placing the line segments on the plane
where in each line segment shares its endpoints with other line segment and thus forming a closed
region on the plane. Here, you need to modify the line clipping algorithm to clip the polygon. The
polygon is tested to see if it is within the display window. The polygon edges are clipped that lie
outside the window boundary. The edge segments that are outside the window are clipped. The
polygon edges must be handled in sequence. The clipping polygon is of two types, namely concave
polygon and convex polygon.

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