Each such reentrant stage of clipping need store only two vertex values and may begin its. Clipping polygons the sutherlandhodgman algorithm clipping polygons would seem to be quite complex. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window. This document describes a c library implementation of a new polygon clipping algorithm.
With respect and admiration, this paper is dedicated to dr. Sutherlandhodgman filled polygon clipping it might appear that we can solve polygon clipping by just using line clipping on the edges, but unfortunately this doesnt work. Sutherland hodgeman polygon clipping algorithm is used for polygon clipping. Sutherlandhodgman clipping n consider subject polygon, sto be clipped against a clip polygon, c n clip each edge of s against c to get clipped polygon. The javascript clipper library performs clipping and offsetting for both lines and polygons. These algorithms are able to clip polygons against ir regular convex planefaced volumes in three dimensions. The sutherlandhodgmanalgorithm is a wellknown algorithm for clipping a polygon against a rectangle. A major application of clipping is to decide whether certain constructs fall within the display window. Reentrant polygon clipping gettysburg college computer science.
Sutherlandhodgman can also be extended into 3d space by clipping the polygon paths based on the boundaries of planes defined by the viewing space. Clipping to the boundary of a circulararc polygon sciencedirect. Reentrant polygon clipping, communications of the acm 10. Polygon clipping is a frequent operation in many fields, including computer graphics, cad, and gis. 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. Pdf clipping a triangle or a convex quadrilateral to a plane is a common operation in computer graphics. Theoretical and experimental analyses show that the. Parallel implementation of polygon clipping using transputer article pdf available in american journal of applied sciences 62 february 2009 with 231 reads how we measure reads. All four boolean clipping operations are supported intersection, union, difference and exclusiveor. 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.
Spatial subsetting clipping as the plot demonstrates, the stations are far more exentsive than polygons of central london. Gpc general polygon clipper library the university of manchester gpc library wikipedia. The art of producing such pictures has become fairly widespread, and the variety of. Clipper the clipper library performs clipping and offsetting for both lines and polygons. We present an algorithm for clipping a polygon or a line against a convex polygonal window. Reentrant polygon clipping reentrant polygon clipping sutherland, ivan e hodgman, gary w. These algorithms are able to clip polygons against irregular convex planefaced volumes in three dimensions, removing the parts of the polygon which lie outside the volume. This process is experimental and the keywords may be updated as the learning algorithm improves. Reentrant polygon clipping communications of the acm. Pdf the below shown convex polygon clipping algorithm is based on the principle of liangbarskys algorithm and. Pdf parallel implementation of polygon clipping using. Given a list of edges in a clip polygon, and a list of vertices in a subject polygon, the following procedure clips the subject polygon against the clip polygon.
It works by extending each line of the convex clip polygon in turn and selecting. Download applet with source 23kb view applet online. An image to be clipped is decomposed into its edges and the edges simultaneously clipped by multiple execution units of a simd computer along pairs of parallel clip planes. We should point out here that one cannot rely on the display device to achieve clipping for two reasons. Fast treatment of lines that are trivially insideoutside the window let px,y be a point to be classified against window w idea. The art of producing such pictures has become fairly widespread, and the variety of approaches available has become. Each such reentrant stage of clipping need store only two vertex values and may begin its processing as soon as the first output vertex from. Successive parallel operations are performed on polygons recomposed using the clipped output edges, until all clipping has been performed. The earclipping process ends for an nvertex input polygon p after n. Each such reentrant stage of clipping need store only two vertex values and may begin its processing as soon as the first output vertex from the preceeding stage is ready. Polygon clipping and filling computer science department.
The weileratherton algorithm overcomes this by returning a set of divided polygons, but is more complex and computationally more expensive, so sutherlandhodgman is used for many rendering applications. C l i p p i n g an arbitrary polygon against an arbitrary polygon has been a complex task. All four boolean clipping operations are supported intersection, union. Since its been some time since the last update, some may be wondering if i no longer plan further updates. The viewing transformation is insensitive to the position of points relative to the viewing volume. 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. Boolean operations and offsetting library in javascript. A generic solution to polygon clipping, communications of the. Reentrant polygon synonyms, reentrant polygon antonyms. It spendsologp time on each edge of the clipped polygon, wherep is the number of window edges, while the sutherlandhodgman algorithm spendsop time per edge. Similar timings were obtained for the reentrant polygon clipping 9 and scanline fill algorithms and listed under method 2. An efficient algorithm for line and polygon clipping. A concave polygon will always have at least one reflex interior anglethat is, an angle with a measure that is between 180 degrees and 360 degrees exclusive some lines containing interior points of a concave polygon intersect its boundary at more than two points.
Each such reentrant stage of clipping need store only two vertex values and may begin its processing as soon as the first. Weiler and atherton 8 were the first to present a clipping algorithm for convex and concave polygons with holes. The triangle is clipped successively against each clip boundary. A simple polygon that is not convex is called concave, nonconvex or reentrant. Gpc is a flexible and highly robust polygon set operations library for use with. Doing this manually would take much time wed have to interrogate the coordinates of each point to see whether or not it falls within one of the polygon boundaries. 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 algorithm demonstrates the practicality of various ideas from computational geometry. Line and polygon clipping techniques on natural images a. Clipping points, lines, and polygons in aligned rectangular.
Such an algorithm considers a polygon to be enclosed by n edges, and by clipping each edge against all the clipping bound aries, seeks to. The clipping algorithms are evaluated by using the three parameters. In geometry a polygon is a flat shape consisting of straightlines that are joined to form a circuit. The sutherlandhodgman algorithm clips a polygon against all edges of the clipping region in turn. A technique frequently used is described in reentrant polygon clipping, suntherland and hodgman, cacm, vol. Hodgroan, reentrant polygon clipping, communications of the acm, volume 17 1974, no. Information about reentrant polygon in the dictionary, synonyms and antonyms. Concave polygon line clipping without degenerate edges. Apply four cases to process all polygon edges to produce sequence of vertices. Assuming you arent clipping in a near horizontal plane, just make sure the critical clipping edge of the clipping polygon is a little larger than the subject polygon s vertical dimensions ie the edge extends a above and below the subject polygon. A general polygon clipping library school of computer. Sutherland hodgman polygon clipping algorithm pracspedia.
The clipping techniques used in this paper is cohensutherland line clipping, liangbarsky line clipping, nichollleenicholl line clipping and sutherlandhodgman polygon clipping. Since both w and s are convex, their intersection is. The correctness of this approach hinges upon meisters twoears theorem 1, which states that every simple polygon with four or more vertices has. A concave polygon will always have at least one reflex interior anglethat is, an angle with a measure that is between 180 degrees and 360 degrees exclusive. Pdf clipping 2d polygons is one of the basic routines in computer graphics. A set of connected lines are considered as polygon.
You could use a polygon clipper to solve this by converting the line into a clipping polygon. Reentrant definition of reentrant by the free dictionary. Parallelized ear clipping for the triangulation and. The term clipping is used to describe the process of finding whether a line or polygon is. A classic problem in computer graphics is to decompose a simple polygon into a collection of triangles whose vertices are only those of the simple polygon. A single polygon can actually be split into multiple polygons can you draw an example. Information and translations of reentrant polygon in the most comprehensive dictionary definitions resource on the web. Reentrant polygon definition of reentrant polygon by the. The algorithm steps from vertex to vertex, adding 0. In two dimensions the algorithms permit clipping against irregular convex windows. The techniques used are descended from vattis polygon clipping method. 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.
A generic solution to polygon clipping, communications of. Pdf efficient triangle and quadrilateral clipping within shaders. Code capable of clipping the polygon against a single boundary is reentered to clip against subsequent boundaries. Information about reentrant polygon in the dictionary, synonyms and. Polygon clipping in java java in general forum at coderanch. I have recently released a beta update to my polygon clipping library clipper that does do linepolygon and lineline clipping where lines can be curves too. Although clipping a convex polygon is algorithmically trivial, doing so efficiently on vector architectures. 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. Jan 10, 2014 spatial subsetting clipping as the plot demonstrates, the stations are far more exentsive than polygons of central london. Gpc general polygon clipper library from the university of. Subject and clip polygons may be convex or concave, selfintersecting, contain holes. This page is about the various possible words that rhymes or sounds like reentrant polygon. Clipping is performed by determining the intersection of the triangle edges with the boundary.
Us6052128a method and apparatus for clipping convex. Assuming you arent clipping in a near horizontal plane, just make sure the critical clipping edge of the clipping polygon is a little larger than the subject polygons vertical dimensions ie the edge extends a above and below the subject polygon. The primary use of clipping in computer graphics is to remove objects, lines, or line segments that are outside the viewing pane. Ii the reentrant polygon clipping by sutherland and h o d g e m a n is limited to convex clip polygons 2, 9, 11. The art of producing such pictures has become fairly widespread, and the variety of approaches available has become manifold. The polygon clipping is required to deal different cases. Polygon and polyline clipping for computer graphic displays. To accomplish this task, it is not enough to clip the lines one by one with e.
The sutherlandhodgman algorithm is an algorithm used for clipping polygons. The term clipping is used to describe the process of finding whether a line or polygon is intersected by another polygon. A new algorithm for boolean operations on general polygons. This paper presents an algorithm for partitioning line segments and circular arcs according to a. Polygon and polyline clipping for computer graphic. The final two algorithms we look at, the vatti and greinerhormann algorithms, are. This section treats clipping of lines against rectangles. Hello, i am stuck on this polygon clipping assignment. Assign p a binary code consisting of a bit for each. The weiler algorithm is more general yet and works for nonconvex polygons.
Use it for writing poetry, composing lyrics for your song or coming up with rap verses. Cohensutherland for line clipping clipping is performed by computing intersections with four boundary segments of the window. Us6052129a method and apparatus for deferred clipping of. Polygons can be of any shape including selfintersecting polygons. First the polygon is clipped against the left edge of the polygon window to get new vertices of the. Subject and clip polygons may be convex or concave, selfintersecting, contain holes, or be comprised of several disjoint contours. Proper usage and audio pronunciation of the word reentrant polygon. Three new algorithms for twodimensional line clipping. If we clip its edges they will disappear, and the polygon will vanish.
A polygon can also be clipped by specifying the clipping window. The existing solutions for polygon clipping are either limited to certain types of polygons or tend to be very complex and time consuming. Hodgman evans and sutherland computer corporation a new family of clipping algorithms is described. Thus, efficient and general polygon clipping algorithms are of great importance. The clipper library performs clipping and offsetting for both lines and polygons. Usually it clips the four edges in the boundary of the clip rectangle. Music of or relating to strings that, when plucked in order, make a discontinuously rising and.
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