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