Cohen-Sutherland Line Clipping Algorithm: When drawing a 2D line on screen, it might happen that one or both of the endpoints are outside. The primary use of clipping in computer graphics is to remove objects, lines, or line This algorithm is more efficient than Cohen-Sutherland algorithm. Department of Computing Science, Umeå University. Computer Graphics & Visualization. Overview. Clipping. ▫ Cohen-Sutherland line clipping algorithm.
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In this algorithm, clippiing the vertices of the polygon are clipped against each edge of the clipping window. For example, if the endpoint codes are andthe logical OR is – the line can be trivally accepted.
It is trivially accepted and needs no clipping.
These 4 bits represent the Top, Bottom, Right, and Left of the region as shown in the following figure. In this type of graphics, images are stored bit by bit and hence it is named Bit-map graphics.
The Cohen-Sutherland algorithm uses a divide-and-conquer strategy.
Cohen-Sutherland Line-Clipping Algorithm
In this method if the string is entirely inside the clipping window, then we keep it. The bits in the 2D outcode represent: If it is partially outside the window, then. Now pick any arbitrary point P Ei on edge E i then the dot product N i. This algorithm uses the clipping window as shown in the following figure. Line can be completely outside of the window This line will be completely removed from the region. If both codes arebitwise OR of the codes yields line lies completely inside the window: Reject line segment if any end point of line appears outside clippkng any boundary.
Line can be partially inside the window We will find intersection point and draw only that portion of line that is inside region. As you proceed around the window, extending each edge and defining an inside half-space and an outside half-space, nine regions are created – the eight “outside” regions and the one “inside”region. It is trivially rejected and needs to be neither clipped nor displayed. It employs parametric line representation and simple dot products.
Each end point of the line segment is then assigned the code of the region in which it lies. It depends on the methods used to generate characters and the requirements of a particular application. Cohen-Sutherland Line Clipping The Cohen-Sutherland line clipping algorithm quickly detects and dispenses with two common and trivial cases.
To determine whether endpoints are inside or outside a window, the algorithm sets up a half-space code for each endpoint. A polygon can also be clipped by specifying the clipping window. To speed up the process this algorithm performs initial tests that reduce number of intersections that must be calculated. These codes identify location of the clippinb point of line. Let N i be compuyer outward normal edge E i.
This site uses Akismet to reduce spam. The algorithm divides a two-dimensional space into 9 regions and then efficiently determines the lines and portions of lines that are visible in the central region of interest the viewport. While processing an edge of a polygon with clipping window, an intersection point is found if edge is not completely inside clipping window and the a vlipping edge from the intersection point to the outside edge is clipped.
This is one of the oldest and most popular line clipping algorithm. On the other hand, if both endpoints of a line lie entirely to one side of the window, the line must lie entirely outside of the window.
Sutherland Hodgeman polygon clipping algorithm is used for polygon clipping. If the region is to the left of the window, the first bit of the code is set to 1. For any endpoint xy of a line, the code can be determined that identifies which region the endpoint lies.
If the region is to the top of the window, the second bit of the code is set to 1. To clip a line, we need to consider only its endpoints. This algorithm is more efficient than Cohen-Sutherland algorithm. It does so by using a 4 bit code called as region code or outcodes. If the character is on the boundary of the clipping window, then we discard that entire character and keep the rest string. A bitmap is a collection of pixels that describes an image.
If the character is on the boundary of the clipping window, then we discard only that portion of character that is outside of the clipping window. Consider the following figure, where the rectangle indicates the window. It can be trivially rejected.
Cokputer a point from a given window is very easy.