These algorithms are complex and the steps of calculation are very. Explain sutherland hodgeman algorithm for polygon clipping. Consider the concave polygon in the picture below by just clipping the lines it is divided in several separate polygons. Earclipping based algorithms of generating highquality.
Hodgman evans and sutherland computer corporation a new family of clipping algorithms is described. This fundamental operation in computer graphics is most often used to constrain drawing to a specified rectangular window, and it has already been successfully solved by a number of reasonably efficient algorithms, which are well known to anyone who has ever picked up a computer graphics textbook. An algorithm that clips a polygon is rather complex. The algorithm can handle arbitrary closed polygons, speci. Polygon clipping is an important operation that computers,execute all the time. Unlike sutherland hodgman polygon clipping algorithm, this algorithm is able to clip concave polygons without leaving any residue behind. Ear clipping based algorithms of generating highquality polygon triangulation gang mei 1, john c. Pdf polygon clipping is an important operation that computers,execute all the time. Quite a few polygon clipping algorithms have been published. The ordering of the outer vertices and the inner vertices must be opposite. That article explains the algorithm and it also explains the code. This clipping is implemented by xedfunction units within the graphics pipeline under most rasterization apis. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window.
The first of all polygons are stored in original form. For example, it would be nice to have x and y in the range 1 to bl. Horizontal decomposition into trapezoids followed by identi cation of monotone polygons. A convex polygon and a convex clipping area are given. An algorithm for polygon clipping, and for determining polygon intersections and unions. A straightforward implementation of this will lead to an on3 algorithm. If we consider the vertices of the polygon oneatatime and keep track of when the edges of the polygon cross the plane, the algorithm is actually quite simple. Then clipping against right edge done, then top edge. The vatti clipping algorithm is used in computer graphics.
Pdf polygon clipping and polygon reconstruction researchgate. Clip a polygon by successively clipping against each infinite clip edge after each clipping a new set of vertices is produced. Multiple polygons may result from clipping a single. The sutherlandhodgman clipping algorithm finds the polygon that is the intersection between an arbitrary polygon the subject polygon and a convex polygon the clip polygon. There are several wellknown polygon clipping algorithms, each having its strengths and weaknesses. We present such an efficient algorithm for clipping arbitrary 2dpolygons. Clipping points, lines, and polygons in aligned rectangular. The techniques used are descended from vattis polygon clipping method. Sutherland and hodgmans polygon clipping algorithm uses a divideandconquer strategy. Create an empty list of output polygons create an empty list of pending crossbacks one for each polygon find all intersections between the polygon and the line. A polygon clipping algorithm receives a polygon and a clipping window as input. Each edge ofthe polygon must be tested against each edge of the. Clipping, in the context of computer graphics, is a method to selectively enable or disable rendering operations within a defined region of interest.
Many algorithms for clipping lines against convex or. A polygon clipper takes as input thevertices of a polygon and returns oneor morepolygons. Also ill only describe one algorithm for each, although in the last section ill mention some others. These algorithms are able to clip polygons against ir regular convex planefaced volumes in three dimensions, removing the parts of the polygon which lie outside. The structure of a clip polygon should be restored efficiently after each clipping operation, to enable efficient execution of the whole clipping process.
Polygon clipping and filling week 3, lecture 5 david breen, william regliand maxim peysakhov department of computer science drexel university. The algorithm steps from vertex to vertex, adding 0, 1, or 2 vertices to the output list at each step. Vattis algorithm 11 can handle the general case in reasonable time. Vertices from the input list are inserted into an output list if they lie on the visible side of the. The algorithm then iterates through the vertices of the polygon, and has the following steps. It is a primitive operation in many fields such as geographic. We need an organized way to deal with all of these cases. Mar 24, 2017 this is algorithm is used to clip the polygon which lies inside the window boundary. Polygon clipping and filling computer science department. Polygon clipping algorithm clip boundary inside outside s boundary inside outside s p boundary inside outside p s i s clip boundary inside outside i p p added to output list i added to output list no output i and p added to output list p for each clip edge scan the polygon and consider the relation between successive vertices of the polygon. It works by extending each line of the convex clip polygon in turn and selecting only vertices from the subject polygon that are on the visible side. I have recently released a beta update to my polygon clipping library clipper that does do line polygon and lineline clipping where lines can be curves too.
This document describes a c library implementation of a new polygon clipping algorithm. Weiler atherton polygon clipping algorithm geeksforgeeks. To implement this polygon clipping algorithm, we usually keep a list of points, commonly called the in list, which holds the resulting clipped polygon. Append a polygon to the output list and make it current. In geometry a polygon is a flat shape consisting of straightlines that are joined to form a circuit. Find file copy path mfogel update readme, add paper describing algorithm ea2d64b feb 2, 2018.
The sutherland and hodgmans polygon clipping algorithm is used in. Sutherland hodgeman polygon clipping algorithm is used for polygon clipping. In rendering complex 3d images it has to be done several thousand times. Is there any other algorithm for the same specifications. Reentrant polygon clipping gettysburg college computer science. Using the hash object to implement a polygon clipping algorithm seth hoffman, geico abstract data with a location component is naturally displayed on a general reference map. The algorithm must evaluate each edge of the polygon against each edge of the clipping window, usually a rectangle. To accomplish this task, it is not enough to clip the lines one by one with e.
Archuletas polygon clipping algorithm 1, long used for all of the. The task is to clip polygon edges using the sutherlandhodgman algorithm. Unlike the sutherlandhodgman and weileratherton polygon clipping algorithms, the vatti algorithm does not restrict the types of polygons that can be used as. Probably the most important thing that i wont be discussing is character clipping. Easier because you only clip against a line instead of a rect or another polygon. An algorithm for polygon clipping, and for determining. Subject and clip polygons may be convex or concave, selfintersecting, contain holes, or be comprised of several disjoint contours. A polygon clipper takes as input thevertices of a polygon and returns oneor more polygons. Line clipping, convex polygon, computer graphics, algorithm complexity. Historically clipping used to be done by the user, not the graphics system. Sutherland hodgman polygon clipping algorithm pracspedia. A generic solution to polygon clipping communications of.
Martinezrueda polygon clipping algorithm, does boolean operation on polygons multipolygons, polygons with holes etc. It allows clipping of any number of arbitrarily shaped subject polygons by any number of arbitrarily shaped clip polygons. A single polygon can actually be split into multiple polygons can you draw an example. Splitting is both easier and harder than polygon clipping.
First the polygon is clipped against the left edge of the polygon window to get new vertices of the. Our algorithm is able to support selfintersecting polygons, meaning that some spatial regions may be covered by two or more polygons. The rst step is to store the polygon as a doubly linked list so that you can quickly remove ear tips. This is algorithm is used to clip the polygon which lies inside the window boundary.
An algorithm for clipping polygons of large geographical data we present an algorithm for overlaying polygonal data with regular grids and calculating the percentage overlap for each cell in the regular grid. Unlike the sutherlandhodgman and weileratherton polygon clipping algorithms, the vatti algorithm does not restrict the types of polygons that can be used as subjects or clips. Polygon clipping sutherlandhodgman algorithm geeksforgeeks. The following example illustrate a simple case of polygon clipping. First, consider a polygon with one hole, as shown in figure10.
The code snippet seems to be taken directly from the corresponding wikipedia article. Clipping any procedure which identifies that portion of a picture which is either inside or outside a picture is referred toas a clipping algorithm or clipping. It solves a series of simple and identical problems that, when combined, solve the overall problem. Polygon clipping algorithm divide and conquer idea. Clipping 2d polygons is one of the basic routines in computer graphics. Input is in the form of vertices of the polygon in clockwise order examples. A vertex is on the in side of the plane is retained in the in list. Several efficient algorithms are available for clipping polygons against rectangular or convex polygons andereev, 1989, maillot, 1992, skala and bui, 2000.
Shawn neely an improved algorithm for clipping one polygon to another is described. Polygon clipping and polygon reconstruction lehrgebiet. Feb 14, 2017 poligon clipping sutherland hodgeman algorithm in hindi computer graphics. Sutherland hodgeman polygon clipping the algorithm begins with an input list of all vertices in the subject polygon.
Next, one side of the clip polygon is extended infinitely in both directions, and the path of the subject polygon is traversed. If the outer vertices are counterclockwise ordered, then the. Its a basic operation in creating graphic output of all kinds. The sutherlandhodgman algorithm clips a polygon against all edges of the clipping region in turn. The sutherlandhodgman algorithm is a algorithm used for clipping polygons. A simple and efficient algorithm for line and polygon. Polygonclipping algorithm right clip boundary bottom clip boundary left clip boundary top clip boundary idea. Multiple polygons may result from clipping a single polygon. For example, we shall allow the polygon in figure 1a to be described by one left. Poligon clipping sutherland hodgeman algorithm in hindi. Polygon clipping and filling week 3, lecture 5 david breen, william regliand maxim peysakhov department of computer science drexel university 1 2 outline. Mathematically, clipping can be described using the terminology of constructive geometry. Then clipping against left edge done and output is stored.
This is achieved by processing all polygon vertices against each clip rectangle boundary in turn. A closed polygon when clipped cthen we may get one or more open c d polygon or dlines. Pdf an algorithm for polygon clipping, and for determining. This method requires a considerable amount of memory. The oldest one from 1974 is called the sutherlandhodgman algorithm. Polygon clipping is one of those humble tasks computers do all the time. Pdf polygon clipping is one of the complex operations in computational geometry. The simplest algorithm, called ear clipping, is the algorithm described in this document. In this paper we present an algorithm for clipping arbitrary polygons, that is conceptually simple, for example, the data structure for the polygons we use is less complex. Poligon clipping sutherland hodgeman algorithm in hindi computer graphics. The sutherlandhodgman algorithm is a wellknown algorithm for clipping a polygon against a rectangle.
Pdf outputsensitive parallel algorithm for polygon clipping. Clipping polygons n cohensutherland and liangbarsky clip line segments against each window in turn n polygons can be fragmented into several polygons during clipping n may need to add edges n need more sophisticated algorithms to handle polygons. The algorithm you present is not the sutherlandhodgman algorithm for clipping against an arbitrary polygon, but the cohensutherland algorithm for clipping against a rectangular viewport. A polygon can be clipped by processing its boundary as a whole against each window edge. With some careful attention to details, the ear clipping can be done in on2 time. Polygon clipping sutherland hodgman algorithm a polygon can also be clipped by specifying the clipping window.
Polygon clipping background theory computer science. Computer graphics sutherlandhodgeman polygon clipping. In order to clip the projected polygons into the projection polygon, im applying the greinerhormann pdf clipping algorithm, which requires that the clipper and the tobeclipped polygons be in the same order i. After clipping, the output segments may not be ordered, and the reconstruction. It consists of an outer polygon and an inner polygon. Tipper 1 and nengxiong xu 2 abstract a basic and an improved ear clipping based algorithm for triangulating simple polygons and polygons with holes are presented. Following figures shows original polygon and clipping of polygon against four windows. Algorithms weiler atherton implementation 2d polygon. As a result, new edges may be added, and existing edges may be discarded, retained, or divided. A simple and efficient algorithm for line and polygon clipping in 2d computer graphics sushil chandra dimri professor and head graphic era university dehradun abstract the most popular lines clipping algorithms are cohensutherland and liangbarsky line clipping algorithm. Background weiler atherton polygon clipping algorithm is an algorithm made to allow clipping of even concave algorithms to be possible. Input is in the form of vertices of the polygon in clockwise order.
A polygon can also be clipped by specifying the clipping window. Clip single polygon using single infinite clip edge repeat 4 times note the generality. Polygon clippingcollection of connected lines is considered aspolygon. Below is a sketch of my algorithm, inspired by the greinerhormann polygon clipping algorithm. Algorithms with better asymptotic order exist, but are more di cult to implement. Clipping polygons the sutherlandhodgman algorithm clipping polygons would seem to be quite complex. Sutherlandhodgman polygon clipping you are encouraged to solve this task according to the task description, using any language you may know. Earclipping based algorithms of generating highquality polygon triangulation 3 2 the proposed algorithms 2.
845 662 850 988 723 1604 1662 362 988 609 501 159 1336 839 116 1235 282 1483 864 180 1515 865 919 1647 486 1070 1323 554 768 157 146 225 597 386 69 66 223 1299