Clipping Concepts – Point, Line, and Polygon

1. What is Clipping?

Clipping is used in computer graphics to improve efficiency and correctness by restricting drawing to the visible area of the screen.

• Removes invisible parts
• Improves rendering performance
• Essential for window-based graphics

2. Clipping Window

A clipping window defines the rectangular region of interest. Objects inside this region are visible, while those outside are clipped.

• Defined by xmin, xmax, ymin, ymax
• Coordinates in world or screen space

3. Types of Clipping

• Point Clipping
• Line Clipping
• Polygon Clipping
• Text and curve clipping

4. Point Clipping

In point clipping, a point is displayed only if it lies inside the clipping window; otherwise, it is discarded.

If (xmin ≤ x ≤ xmax) AND (ymin ≤ y ≤ ymax)
    Point is visible
Else
    Point is clipped

5. Line Clipping

Line clipping determines which portions of a line segment lie inside the clipping window and displays only those portions.

• May be fully visible
• Fully invisible
• Partially visible

6. Polygon Clipping

Polygon clipping clips a polygon against a clipping window and produces a new polygon that lies completely inside the window.

• Used for filled areas
• More complex than line clipping
• Preserves polygon shape

7. Window and Viewport

The window defines the area in world coordinates, while the viewport defines the area on the display device where the window contents are mapped.

• Window → World coordinates
• Viewport → Device coordinates

8. Importance of Clipping

• Reduces unnecessary drawing
• Improves performance
• Ensures correct visual output

9. Applications of Clipping

• Window-based user interfaces
• 2D and 3D graphics rendering
• CAD and GIS systems

Practice Questions

1. What is clipping?
2. Define clipping window.
3. Explain point clipping.
4. Differentiate line and polygon clipping.
5. Why is clipping important?

Practice Task