For other convex polygon clipping windows, cyrusbeck algorithm is used. In gis, however, the clipping area is generally an arbitrarilyshaped polygon. Sutherland and hodgmans polygonclipping algorithm uses a divideandconquer strategy. It is used in computer graphics especially 2d graphics to reduce the complexity of a scene being displayed by eliminating parts of a polygon that do not. Sutherlandhodgman polygon clipping algorithm thanks again for watching. The sutherlandhodgman algorithm is an algorithm used for clipping polygons. An algorithm for polygon clipping, and for determining. Sutherland hodgeman polygon clipping the algorithm begins with an input list of all vertices in the subject polygon.
The cohensutherland algorithm can be used only on a rectangular clip window. The execution time for this example using this algorithm is measured to be half of what is required by the standard sutherlandhodgman reentrant polygon clipping algorithm view show abstract. Input is in the form of vertices of the polygon in clockwise order. It is performed by processing the boundary of polygon against each window corner or edge. A convex polygon and a convex clipping area are given. Weiler atherton polygon clipping algorithm geeksforgeeks. It is used in the areas like computer graphics, games development and others where clipping of polygon is needed. The polygon clipping algorithm deals with four different clipping cases. 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. Next, one side of the clip polygon is extended infinitely in both directions, and the path of the subject polygon is traversed. We will remove or clip the part that is outside the window. Martinezrueda polygon clipping algorithm, does boolean operation on polygons multipolygons, polygons with holes etc. Explain weiler atherton polygon clipping algorithm in detail. 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.
Polygonclipping algorithm right clip boundary bottom clip boundary left clip boundary top clip boundary idea. First of all entire polygon is clipped against one edge, then resulting polygon is considered, then the polygon is considered against the second edge, so on for all four edges. Explain weileratherton polygon clipping algorithm and. A powerful but somewhat more complex clipping algorithm developed by weiler and atherton meets this requirement. If you liked it pls make it a point to comment below. Consider each edge e of clipping area and do following.
Algorithm for each boundary b in l, r, t, b if p 1 outside and p 2 inside output intersection output p 2 if p 1 inside and p 2 inside output p 2 if p 1 inside and p 2 outside output intersection if p 1 outside and p 2 outside do nothing. Computer graphics sutherlandhodgeman polygon clipping. Vattis algorithm 11 can handle the general case in reasonable time. For a polygon and clipping window shown in figure below give the list of vertices after each boundary clipping. Explain sutherland hodgeman algorithm for polygon clipping. These new vertices are used to clip the polygon against right edge, top edge, bottom edge, of the clipping window as shown in the following figure. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window. It allows clipping of a subject or candidate polygon by an arbitrarily shaped clipping polygonarearegion it is generally applicable only in 2d.
Let r be the rectangular window whose lower lefthand corner is at l 3, 1 and upper righthand corner is at r 2, 6. The code snippet seems to be taken directly from the corresponding wikipedia article. 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. This algorithm is more efficient than cohensutherland line clipping algorithm and can be extended to 3dimensional clipping. This is algorithm is used to clip the polygon which lies inside the window boundary. A polygon clipper takes as input thevertices of a polygon and returns oneor morepolygons. Clipping polygons the sutherlandhodgman algorithm clipping polygons would seem to be quite complex. Check if it is possible to create a polygon with given n sides. This polygon clipping algorithm does not work for self intersecting polygons, although some methods have been proposed to be able to solve this issue also, and have successfully worked. The oldest one from 1974 is called the sutherlandhodgman algorithm. Original polygon vertices are v1, v2, v3, v4, and v5. Although there are specialized algorithms for rectangle and polygon clipping, it is important to note that other graphic primitives can be clipped by repeated application of the line clipper.
The liangbarsky algorithm is a line clipping algorithm. It works by extending each line of the convex clip polygon in turn and selecting. Sutherland hodgman polygon clipping algorithm with. The algorithm is specifically fast and capable of working with polygons of all types.
Polygonclipping 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. A closed polygon when clipped cthen we may get one or more open c d polygon or dlines. The result of polygon clipping is a new polygon representing a. Let me explain the algorithm of sutherlandhodgman using the above situation. Polygon clipping sutherlandhodgman algorithm point clipping algorithm in computer graphics. The region code for point x, y is set according to the scheme. Sorry but i forgot to mention that the circle is just an example. Intersection 20 p1, v7, p0, p3, v5, p2 20 21 boolean special cases if polygons dont intersect. Its a basic operation in creating graphic output of all kinds. The sutherland hodgeman polygon clipping algorithm. Line clipping set 2 cyrus beck algorithm line clipping set 1 cohensutherland algorithm sum of internal angles of a polygon. Polygon clipping is one of those humble tasks computers do all the time. This algorithm is considered to be the faster parametric lineclipping algorithm.
A single polygon can actually be split into multiple polygons can you draw an example. But what kind of algorithm can i use to get a polygon like in 3. The sutherland hodgeman polygon clipping algorithm slideshare. The sutherlandhodgman algorithm clips a polygon against all edges of the clipping region in turn. Sutherland hodgeman polygon clipping algorithm is used for polygon clipping.
Greiner and hormann 1998 propose a simple and timeefficient algorithm that can clip arbitrary polygons, including concave and selfintersecting polygons with holes. That article explains the algorithm and it also explains the code. However, it can be used in 3d through visible surface determination and with improved. Polygon clipping is a frequent operation in many fields, including computer graphics, cad, and gis.
We begin at the starting vertex and continue along the same edge from 1 to 2 of the subject polygon as it enters the clip polygon. This algorithm defines the polygon to be clipped as a subject polygon and the clipping region is the clip polygon. The task is to clip polygon edges using the sutherlandhodgman algorithm. It is used in areas like computer graphics and games development where clipping of polygons is needed. Algorithm has to calculate more number of intersection points over window boundary.
This section treats clipping of lines against rectangles. Clip a polygon by successively clipping against each infinite clip edge after each clipping a new set of vertices is produced. Let v 1 v 2 v 3 v 4 v 5 v 6 be the clipping window and p 1 p 2 p 3 p 4 p 5 p 6 be the polygon. Vertices from the input list are inserted into an output list if they lie on the visible side of the.
Clipper an open source freeware polygon clipping library. Example case 2 polygons asorted array in the code and botherpolygon array in the code. It allows clipping of a subject or candidate polygon by an arbitrarily shaped clipping polygonarearegion. The algorithm you present is not the sutherlandhodgmanalgorithm for clipping against an arbitrary polygon, but the cohensutherlandalgorithm for clipping against a rectangular viewport. 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. Polygon clipping sutherland hodgman algorithm a polygon can also be clipped by specifying the clipping window.
The algorithm describes both the subject and the clip polygon by a. The following example illustrate a simple case of polygon clipping. We will use the following algorithms for polygon clippingsutherlandhodgeman polygon clipping algorithm. Check if it is possible to create a polygon with a given angle. It solves a series of simple and identical problems that, when combined, solve the overall problem. In geometry a polygon is a flat shape consisting of straightlines that are joined to form a circuit.
Similarly, this clipping works for convex polygons. Polygon clippingcollection of connected lines is considered aspolygon. Pdf parallel implementation of polygon clipping using. A polygon can be clipped by processing its boundary as a whole against each window edge. After clipping each boundary the new vertices are as shown in figure above. Example of cohensutherland line clipping algorithm.
An algorithm for polygon clipping, and for determining polygon intersections and unions. Handles nonconvex polygons and multiple clipping areas. Indeed, archuletas polygon clipping algorithm 1, long used for all of the hiddensurface pictures at the university of utah, is just such an extension. For example, the number in fig a indicates the order in which the edges and portion of edges are traced. The algorithm steps from vertex to vertex, adding 0. Opengl sutherlandhodgman polygon clipping algorithm in. The issue is that depending on where the convex polygon is, the order in which i find the intersection points changes. First the polygon is clipped against the left edge of the polygon window to get new vertices of the polygon. Thus, efficient and general polygon clipping algorithms are of great importance. There are several wellknown polygon clipping algorithms, each having its strengths and weaknesses.
Unlike sutherland hodgman polygon clipping algorithm, this algorithm is able to clip concave polygons without leaving any residue behind. We will be discussing cyrusbeck algorithm in next set. Clip single polygon using single infinite clip edge. Subramanian usage click on the canvas to seed the points of the polygon press d to draw the seeded polygon drag the mouse cursor to draw the required clip rectangle press c to clip the required polygon section. Is there a way to guarantee that the intersection points are always found in the same order. This is achieved by processing all polygon vertices against each clip rectangle boundary in turn. It accepts an ordered sequence of verices v1, v2, v3. The sutherland hodgman algorithm performs a clipping of a polygon against each window edge in turn. Computer graphics sutherlandhodgeman polygon clipping with computer graphics tutorial, line generation algorithm, 2d transformation, 3d computer.
The download package contains the librarys full source code written. Such an algorithm considers a polygon to be enclosed by n edges, and. The algorithm terminates when the entire border of the original subject polygon has been traced exactly once. Sutherlandhodgman polygon clipping algorithm youtube. Sutherlandhodgman polygon clipping complexity of this algorithm will increase if number of edges of polygon increase. The output of each case is input for the next case. Background weiler atherton polygon clipping algorithm is an algorithm made to allow clipping of even concave algorithms to be possible.