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. C l i p p i n g an arbitrary polygon against an arbitrary polygon has been a complex task. If we clip its edges they will disappear, and the polygon will vanish. For example, suppose you have a shape in the base layer, a photograph in the layer above it, and text in the topmost layer. Polygon and polyline clipping for computer graphic. Information and translations of reentrant polygon in the most comprehensive dictionary definitions resource on the web. A single polygon can actually be split into multiple polygons can you draw an example.
In geometry a polygon is a flat shape consisting of straightlines that are joined to form a circuit. We should point out here that one cannot rely on the display device to achieve clipping for two reasons. 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. A clipping mask is a group of layers to which a mask is applied. Use it for writing poetry, composing lyrics for your song or coming up with rap verses. 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. Subject and clip polygons may be convex or concave, selfintersecting, contain holes, or be comprised of several disjoint contours. 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. Polygon clipping background theory computer science. The sutherlandhodgmanalgorithm is a wellknown algorithm for clipping a polygon against a rectangle. 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. Clipping, in the context of computer graphics, is a method to selectively enable or disable rendering operations within a defined region of interest. Reentrant polygon clipping, communications of the acm 10.
The bottommost layer, or base layer, defines the visible boundaries of the entire group. Clipperan open source freeware library for clipping and offsetting lines. The algorithm steps from vertex to vertex, adding 0. A new algorithm for boolean operations on general polygons. Efficient triangle and quadrilateral clipping within shaders. Reentrant polygon clipping reentrant polygon clipping sutherland, ivan e hodgman, gary w.
Boolean operations and offsetting library in javascript. Concave polygon line clipping without degenerate edges. These math sheets can be printed as extra teaching material for teachers, extra math practice for kids or as homework material parents can use. Performance comparison with 2 well known polygon clipping libraries. A general polygon clipping library school of computer. Each such reentrant stage of clipping need store only two vertex values and may begin. Polygon clipping is one of those humble tasks computers do all the time. 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.
These algorithms are able to clip polygons against irregular convex planefaced. Us4208810a clipping polygon faces through a polyhedron. Very optimized boolean operations on polygon sets see the test results below highquality api. 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. We present an algorithm for clipping a polygon or a line against a convex polygonal window.
Weiler and atherton 8 were the first to present a clipping algorithm for convex and concave polygons with holes. Wherever you are, get your redlining and other pdf work done with drawboard pdf and windows 10. You could use a polygon clipper to solve this by converting the line into a clipping polygon. Polygon clipping and filling week 3, lecture 5 david breen, william regliand maxim peysakhov department of computer science drexel university 1 2 outline polygon clipping sutherlandhodgman, weileratherton polygon filling scan filling polygons flood filling polygons. The sutherlandhodgman algorithm clips a polygon against all edges of the clipping region in turn. This document describes a c library implementation of a new polygon clipping algorithm. A generic solution to polygon clipping communications of. 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. 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.
To accomplish this task, it is not enough to clip the lines one by one with e. 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. All four boolean clipping operations are supported intersection, union, difference and exclusiveor. Clip a concave polygon against an infinite line without direction actually a polygon against a plane in 3d but the problem is similar i think. 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. I have to clip a polygon with another polygon file. Each such reentrant stage of clipping need store only two vertex values and may. To be clipped, the polygon features must be editable and visible. Clipping points, lines, and polygons in aligned rectangular. Polygon clipping is a frequent operation in many fields, including computer graphics, cad, and gis. Usually it clips the four edges in the boundary of the clip rectangle. You can clip polygon features that touch or are within a buffered distance of a selected feature using the clip command. Similar timings were obtained for the reentrant polygon clipping 9 and scanline fill algorithms and listed under method 2.
A number of features set clipper apart from other clipping libraries. Thus, efficient and general polygon clipping algorithms are of great importance. When an imported graphic includes more than one path or alpha channel, you can choose which path or alpha channel to use for the clipping path. Pdf clipping 2d polygons is one of the basic routines in computer graphics. Clipping polygons the sutherlandhodgman algorithm clipping polygons would seem to be quite complex.
A generic solution to polygon clipping, communications of. In two dimensions the algorithms permit clipping against irregular convex windows. A generic solution to polygon clipping, communications of the. Polygon clipping sutherlandhodgman algorithm geeksforgeeks. Abstract clipping a triangle or a convex quadrilateral to a plane is a common operation in computer graphics. This clipping is implemented by fixed function units within the graphics pipeline under most rasterization application programming interfaces apis. Code capable of clipping the polygon against a single boundary is reentered to clip against subsequent boundaries. These algorithms are able to clip polygons against irregular convex. Shawn neely an improved algorithm for clipping one polygon to another is described. 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. Are you new to inkscape learn more about inkscape, an open source vector graphics editor, in this free, communitycreated beginners guide this guide is a living document. Hi, i am a new postgis user, so sorry if my request seems trivial for someone.
Music of or relating to strings that, when plucked in order, make a discontinuously rising and. These algorithms are able to clip polygons against ir regular convex planefaced volumes in three dimensions. Sutherlandhodgman polygon clipping you are encouraged to solve this task according to the task description, using any language you may know. This process is experimental and the keywords may be updated as the learning algorithm improves. There are several wellknown polygon clipping algorithms, each having its strengths and weaknesses. The existing solutions for polygon clipping are either limited to certain types of polygons or tend to be very complex and time consuming. If you find something that is confusing, wrong, or otherwise needs. This page is about the various possible words that rhymes or sounds like reentrant polygon. This is a suitable resource page for third graders, teachers and parents. Information about reentrant polygon in the dictionary, synonyms and antonyms. Although clipping a convex polygon is algorithmically trivial, doing so efficiently on vector architectures such as gpus.
Mathematically, clipping can be described using the terminology of constructive geometry. 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. It solves a series of simple and identical problems that, when combined, solve the overall problem. First the polygon is clipped against the left edge of the polygon window to get new vertices of the. There are two wellknown polygon clipping algorithms, the sutherlandhodgman and the liangbarsky algorithms see ivan e. Input is in the form of vertices of the polygon in clockwise order examples. The algorithm demonstrates the practicality of various ideas from computational geometry. Currently i use sutherlandhodgman but the resulting polygons sometimes contains zeroarea parts created from degenerate edges and it also do not support polygons containing holes. Parallel implementation of polygon clipping using transputer article pdf available in american journal of applied sciences 62 february 2009 with 210 reads how we measure reads. Pdf parallel implementation of polygon clipping using. Sutherlandhodgman can also be extended into 3d space by clipping the polygon paths based on the boundaries of planes defined by the viewing space. Successive parallel operations are performed on polygons recomposed using the clipped output edges, until all clipping has been performed. We have compared the performance and memory utilization of the com version of polygonlib with those of 2 well known polygon clipping libraries.
Barsky, an analysis and algorithm for polygon clipping. The viewing transformation is insensitive to the position of points relative to the viewing volume. Springer nature is making coronavirus research free. The term clipping is used to describe the process of finding whether a line or polygon is intersected by another polygon. An alpha channel is an invisible channel that defines transparent areas of a. For example, to clip bounding volumes generated in. A major application of clipping is to decide whether certain constructs fall within the display window. Us6052128a method and apparatus for clipping convex. It is increasingly interesting to perform clipping in programmable stages as well.
Consider the concave polygon in the picture below by just clipping the lines it is divided in several separate polygons. We should point out here that one cannot rely on the display device to achieve clipping. 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. The sutherlandhodgman algorithm is an algorithm used for clipping polygons. Clipping an arbitrary polygon against an arbitrary polygon has been a complex task. Indesign can crop an imported eps, tiff, or photoshop graphic using the clipping path or alpha channel saved with the file. It works by extending each line of the convex clip polygon in turn and selecting. This means that it is actively being edited and continuously being improvedand you can contribute. The clipper library performs clipping, and offsetting of both lines and polygons. The term clipping is used to describe the process of finding whether a line or. Pdf efficient triangle and quadrilateral clipping within shaders. The javascript clipper library performs clipping and offsetting for both lines and polygons. Drawboard pdf provides relevant industry tools from drafters and detail oriented engineersall the way to project managers. An efficient algorithm for line and polygon clipping.
Two possible cases in bresenhams line drawing algorithm. A set of connected lines are considered as polygon. Hodgroan, reentrant polygon clipping, communications of the acm, volume 17 1974, no. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window. Successive parallel operations are performed on polygons recomposed using the clipped output edges, until all clipping.
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. The techniques used are descended from vattis polygon clipping method. The reentrant polygon clipping by sutherland and hodgeman is limited to convex clip polygons 2, 9, 11. As another example, assume there are a group of freerotating cameras. Sutherland hodgman polygon clipping algorithm pracspedia. The existing solutions for polygon clipping are either limited to certain types of polygon or tend to be very complex and time consuming. The primary use of clipping in computer graphics is to remove objects, lines, or line segments that are outside the viewing pane. A convex polygon and a convex clipping area are given.
Polygon clipping and splitting algorithms are described in the literature for a specific geometry. Reentrant definition of reentrant by the free dictionary. Pdf clipping a triangle or a convex quadrilateral to a plane is a common operation in computer graphics. While processing an edge of a polygon with clipping window, an intersection point is found if edge. Reentrant polygon definition of reentrant polygon by the. The polygon clipping is required to deal different cases. Theoretical and experimental analyses show that the. Its a basic operation in creating graphic output of all kinds. A rendering algorithm only draws pixels in the intersection between the clip region and the scene model. Reentrant polygon synonyms, reentrant polygon antonyms.
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. The task is to clip polygon edges using the sutherlandhodgman algorithm. Hodgman evans and sutherland computer corporation a new family of clipping algorithms is described. A simple polygon that is not convex is called concave, nonconvex or reentrant. Us4208810a us05940,818 us94081878a us4208810a us 4208810 a us4208810 a us 4208810a us 94081878 a us94081878 a us 94081878a us 4208810 a us4208810 a us 4208810a authority us unite. Sutherland hodgeman polygon clipping algorithm is used for polygon clipping.
1458 656 646 1105 1105 1042 599 16 1362 1506 1351 857 479 915 1071 331 549 1316 304 1483 796 191 881 30 1365 1180 1130 1096 45 931 284 94