**INTRODUCTION**

The procedure that identifies the portions of a picture
that are either inside or outside of a specified region of space is referred to
as clipping. The region against which an object is to be clipped is called a
clip window or clipping window. It is in a rectangular in shape.

The clipping algorithm determines which points, lines or
portions of lines lay within the clipping window. These points, lines or
portions of lines are retained for display. All others are discarded. We will
consider algorithms for clipping the following primitive types

• Point Clipping

• Line Clipping

• Polygon Clipping

**POINT CLIPPING**

Assuming that the clip window is a rectangle in standard
position, we save a point P = (x, y)
for display if the following inequalities are satisfied:

XW

_{min}≤ X ≤ XW_{max}
yw

_{min}≤ y ≤ yw_{max}
where the edge of the clip window (xw

_{min}, xw_{max}, yw_{min}, yw_{max}) can be either the world-coordinate window boundaries or viewport boundaries. If any one of these four inequalities is not satisfied, the point is clipped (not saved for display).
Although point clipping is applied less often than line
or polygon clipping, some application may require a point-clipping procedure.

**Point Clipping**

**LINE CLIPPING**

The lines are said to be interior to the clipping window
and hence visible if both end points are interior to the window, e.g., line
psp4 in the figure. However, if both end points of a line are exterior to the
window, the line is not necessarily completely exterior to the window, e.g.,
line p

_{7}p_{8}in the figure. If both end points of a line are completely to the right of, completely to the left of, completely above, or completely below the window, then the line is completely exterior to the window and hence invisible, e.g., line p_{1}p_{2}and p_{9}p_{10 }in the figure.**Line Clipping**

•
Find the part of a line inside the clip window

The lines which across one or more clipping boundaries
require calculation of multiple intersection points to decide the visible
portion of them. To minimize the intersection calculations and to increase the
efficiency of the clipping algorithm, initially, completely visible and
invisible lines are identified and then intersection points are calculated for
remaining lines.

**Line Clipping**

• Find the part of a line inside the clip
window

## No comments:

## Post a Comment