2. Introduction
• The line clipping is a process in which we can cut the part of the line,
which lies outside the view pane. Only those lines are visible, which lie
inside the view pane.
• The Cohen-Sutherland line clipping algorithm is a common method
used in computer graphics to efficiently clip lines against a rectangular
clipping window. Line clipping is an important task in computer
graphics because it allows us to selectively display only the portions of
a line that are visible within a given viewport or window while
discarding the portions that lie outside of it. This can improve the
overall performance and visual quality of a graphics application,
particularly when rendering complex scenes.
• In this presentation, we will introduce the Cohen-Sutherland line
clipping algorithm, explain how it works, demonstrate its use with an
example, discuss its advantages and limitations.
5. How the algorithm works
• We will divide the view pane into nine equal segments that only serve the
viewport.
• We will represent the top, bottom, left, and right corner of the window with
4 bits. These 4 bits can be described with the following point:
• If an object lies within any particular corner position, that corner value will
be 1, else it will be 0.
• The allocation of bits depends on “TBRL” (Top, Bottom, Right, Left) rule.
• Suppose, if the point of a line appears in the top-left corner, then according
to TBRL, the value is 1001. We will allot the bits as-
• For the top corner, because the object is present at the top corner.
• For the bottom corner, because the object does not lie at the bottom.
• For the right corner, because the object does not lie at the right side.
• For the left corner, because the object lies at the top-left corner.
• In this way, we check TBRL for each segment and allot the bits accordingly.
7. Line Viewing
• In Cohen- Sutherland Algorithm we will divide the lines into
following Sections
• Visible Line: When both points (starting and ending) of the
line are entirely situated inside the window.
• Invisible Line: When both points (Starting and ending) of
the line are completely situated outside the window.
• Clipped Line: Everyline has two endpoints. Let (x0, y0) and
(x1, y1) are points of the line. If one point of the line situated
inside the window and the other one is outside the
window, then the line is known as Clipped Line.
8. Steps when using the Algorithm
1.Determine the region codes for the endpoints of
the line.
2.Check if both endpoints are within the clipping
window (region code = 0000). If they are, the
line is completely inside the window and can be
displayed.
3.If both endpoints have a region code that has a
common bit value of 1, the line is completely
outside the clipping window and can be rejected.
9. Step 4
• If the line is partially inside the clipping window, perform line
clipping using the following steps:
• a. Find the intersection of the line with the clipping window
boundaries.
• b. If an endpoint lies outside the clipping window, replace it
with the intersection point.
• c. Recalculate the region codes for the new endpoints.
• d. Repeat steps b and c until both endpoints lie within the
clipping window or the line is completely outside.
11. Example
• Line AB is a clipped case.
• The line CD is completely visible.
• Line EF is completely invisible.
• Line GH is a clipped case.
• Line KL is completely invisible.
• Line IJ is a clipped case.
12. Endpoints of the Lines
• The endpoints of lines are lies as follow
• A ? 0000
• B ? 1010
• C ? 0000
• D ? 0000
• E ? 0100
• F ? 0100
• G ? 0001
• H ? 0000
• I ? 0000
• J ? 0010
• K ? 1000
• L ? 1000
13. Applications of the Algorithm
1. Line Clipping in Computer Graphics: The primary application
of the Cohen-Sutherland algorithm is in line clipping for
rendering graphics. It efficiently determines which portions of
a line lie inside or outside a given clipping window, allowing
for the rendering of only the visible parts of the line. This helps
optimize the rendering process and improve the overall
efficiency of graphics systems.
2. Window and Viewport Clipping: The Cohen-Sutherland
algorithm can be used for window and viewport clipping in
graphical user interfaces (GUIs). It determines which portions
of a window or viewport lie within the visible area, ensuring
that only the visible content is displayed. This is particularly
useful when working with large documents or images that
need to be displayed within a limited viewing area.
14. Applications
1. Line Clipping in CAD Systems: Computer-aided design (CAD)
systems often make use of the Cohen-Sutherland algorithm
for line clipping operations. It enables the efficient
manipulation and display of lines and geometries within the
CAD environment. The algorithm ensures that only the visible
portions of lines are displayed, allowing designers and
engineers to work with accurate and visually appealing
representations.
2. Image Processing and Digital Photography: In image
processing and digital photography applications, the Cohen-
Sutherland algorithm can be utilized for cropping or trimming
images. It allows for the precise selection of regions of
interest and removal of unwanted portions, resulting in
improved composition and visual aesthetics.
15. Advantages of the algorithm
• Ability to handle arbitrary clipping windows: The algorithm can handle
clipping windows of any shape, not just rectangular ones. This makes it
more flexible and versatile than other clipping algorithms that are
limited to rectangular windows.
• Efficiency in handling many different types of lines: The algorithm is
efficient in handling many different types of lines, including vertical,
horizontal, and diagonal lines. It can also handle lines of any slope,
including those that are steep or nearly horizontal.
• Easy to implement: The algorithm is relatively easy to implement and
can be adapted to a variety of programming languages and
environments.
16. Limitations
• Inability to handle curved lines: The algorithm is not capable of
handling curved lines, which can be a significant limitation in some
cases. Other algorithms, such as the Cyrus-Beck algorithm, can handle
curved lines but may not be as efficient as the Cohen-Sutherland
algorithm.
• Limited to line clipping: The Cohen-Sutherland algorithm is designed
specifically for line clipping and cannot be used for other types of
clipping, such as polygon clipping.
• Requires pre-processing: The algorithm requires pre-processing to
compute the two-bit codes for each point or line segment, which can
add some overhead to the overall clipping process.
