Gpc general polygon clipper library from the university of. Dda algorithm digital differential analyzer dda algorithm is the simple line generation algorithm which is explained step by step here. The sutherlandhodgman algorithm clips a polygon against all edges of the clipping region in turn. For example, we shall allow the polygon in figure 1a to be described by one left. It solves a series of simple and identical problems that, when combined, solve the overall problem. An algorithm for polygon clipping, and for determining. A polygon can be clipped by processing its boundary as a whole against each window edge. Computer graphics sutherlandhodgeman polygon clipping. Clipping, in the context of computer graphics, is a method to selectively enable or disable rendering operations within a defined region of interest. Ear clipping based algorithms of generating highquality polygon triangulation gang mei 1, john c. The sutherlandhodgman algorithm is an algorithm used for clipping polygons. The polygon clipping is required to deal different cases. Michael leonov has compiled a comparison of polygon clippers, including gpc. The novelty of these fields makes it difficult to design a course or to a write a book covering their basic concepts.
An efficient algorithm for line and polygon clipping springerlink. 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. It is performed by processing the boundary of polygon against each window corner or edge. Some of the treatises on graphics focus on the hardware and methods of current interest while treatises on image processing often emphasize applications and classical signal processing. The simple problem is to clip a polygon against a single infinite clip edge. Given a set of 2d lines or polygons and a window, clip the lines or polygons to their regions that are inside the window.
Sutherland hodgeman polygon clipping algorithm is used for polygon clipping. The task is to clip polygon edges using the sutherlandhodgman algorithm. Polygon clipping convert a polygon into one or morepolygons that form the intersection of the original with the clip window computer graphics 1546234 sutherlandhodgman polygon clipping algorithm subproblem. Pdf polygon clipping and polygon reconstruction researchgate. Mathematically, clipping can be described using the terminology of constructive geometry.
A simple and efficient algorithm for line and polygon. A rendering algorithm only draws pixels in the intersection between the clip region and the scene model. David kennisons polypack, a fortran library based on the vatti algorithm. A major application of clipping is to decide whether certain constructs fall within the display window. In addition to geometry algorithms, we also have an upgraded site. Download book pdf algorithms for graphics and image processing pp 337357 cite as. We present an algorithm for clipping a polygon or a line against a convex polygonal window. It consists of an outer polygon and an inner polygon. The term clipping is used to describe the process of finding whether a line or polygon is intersected by another polygon. First, the display area may be only a subset of the display screen for example, a part of the screen may be.
Viewing transforms, 2d clipping, cohensutherland outcode algorithm, polygon clipping, sutherlandhodgman algorithm, generalized clipping. Finally, the sh polygon clipping algorithm is reduced to line segment clipping. Line and circle generationline generation dda and bresenhams algorithm, thick line segments, antialising of lines, circle generation dda and bresenhams algorithm, character generation. First, consider a polygon with one hole, as shown in figure10. Quite a few polygon clipping algorithms have been published. Sutherlandhodgman algorithm contd the algorithm clips every polygon edge against each clipping line use an output list to store newly clipped polygon vertices with each polygon edge, 1 or 2 vertices are added to the output list s p. Easier because you only clip against a line instead of a rect or another polygon. 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. Usually it clips the four edges in the boundary of the clip. This is achieved by processing all polygon vertices against each clip rectangle boundary in turn. 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. If the outer vertices are counterclockwise ordered, then the. Tipper 1 and nengxiong xu 2 abstract a basic and an improved ear. Three new algorithms for twodimensional line clipping. Below is a sketch of my algorithm, inspired by the greinerhormann polygon clipping algorithm. Handles nonconvex polygons and multiple clipping areas. After clipping, the output segments may not be ordered, and the reconstruction. Polygon clipping ppt polygon convex set free 30day.
A generic solution to polygon clipping communications of. A single polygon can actually be split into multiple polygons can you draw an example. The sutherlandhodgman algorithm is a wellknown algorithm for clipping a polygon against a rectangle. Algorithms for graphics and image processing springerlink. Polygon clipping and polygon reconstruction citeseerx. 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. The vatti clipping algorithm is used in computer graphics. After discussing three basic polygon clipping algorithms, a different approach is proposed, explaining the principles of a new algorithm and presenting it step by step. Several efficient algorithms are available for clipping polygons against rectangular or convex polygons andereev, 1989, maillot, 1992, skala and bui, 2000. A hiddensurface aic43rithm with antialiasing edwin. We should point out here that one cannot rely on the display device to achieve clipping. The result of clipping a primitive by a plane is the intersection of the primitive and the positive halfspace bounded by the plane. The modifications are performed so as to allow easy extension of the 2d algorithm to 3d. 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.
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 algorithm 7 8 foreachpolygon p p p foreachclipping edge there are 4 clip polygon pto clipping edge foreachedge in polygon p check clipping cases there are 4 case 1. The algorithm steps from vertex to vertex, adding 0. All books are in clear copy here, and all files are secure so dont worry about it.
Poligon clipping sutherland hodgeman algorithm in hindi. Subject and clip polygons may be convex or concave, selfintersecting, contain holes, or be comprised of several disjoint contours. Properties of polygon planner set of ordering points. Kai hormann computer graphics group, university of erlangen abstract clipping 2d polygons is one of the basic routines in computer graphics. Sutherlandhodgman can also be extended into 3d space by clipping the polygon paths based on the boundaries of planes defined by the viewing space. That article explains the algorithm and it also explains the code. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window. A polygon can also be clipped by specifying the clipping window.
Consider each edge e of clipping area and do following. 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 principles of optimization presented for this class of parallel algorithm extend to other algorithms and architectures. Splitting is both easier and harder than polygon clipping. An analysis and algorithm for polygon clipping communications of.
Input is in the form of vertices of the polygon in clockwise order. Here is the full list of algorithm titles in the geometry algorithms archive. In rendering complex 3d images it has to be done several thousand times. Polygon clipping unlike line clipping where we selectively clipped against each edge, here we successively clip a polygon against all four edges of the clip rectangle s. The techniques used are descended from vattis polygon clipping method. 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.
To accomplish this task, it is not enough to clip the lines one by one with e. A convex polygon and a convex clipping area are given. The full table of contents toc gives a more detailed listing. Reentrant polygon clipping communications of the acm.
Martinezrueda polygon clipping algorithm, does boolean operation on polygons multipolygons, polygons with. The ordering of the outer vertices and the inner vertices must be opposite. This site is like a library, you could find million book here by using search box in the header. We present such an efficient algorithm for clipping arbitrary 2dpolygons. This document describes a c library implementation of a new polygon clipping algorithm. Cohensutherland and cyrusbeck line clipping algorithms. The cs implementation is further improved by reducing the number of redundant comparisons, and the amount of floatingpoint computation per intersection point. More than 50 million people use github to discover, fork, and contribute to over 100 million projects. All of the po lygons in a pixel are clipped against some front unclipped edge into two lists of polygons. Sutherlandhodgman algorithm 7 8 foreachpolygon p p p foreachclipping edge there are 4 clip polygon pto clipping edge foreachedge in polygon p. Simple and efficient 2d and 3d span clipping algorithms. In the following three algorithms, we refer the one point of line as x 0, y 0 and the second point of line as x 1, y 1. Clipping polygons the sutherlandhodgman algorithm clipping polygons would seem to be quite complex. Check it out to discover how geometry evolved from ancient to modern times.
A set of connected lines are considered as polygon. 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. It allows clipping of any number of arbitrarily shaped subject polygons by any number of arbitrarily shaped clip polygons. Earclipping based algorithms of generating highquality. Basic conceptstypes of graphics devices, display file structure, display file interpreter, display processors, graphics file format, bmp, tiff, pcx, gif. 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. These algorithms are able to clip polygons against irregular convex planefaced volumes in three dimensions. The algorithm can handle arbitrary closed polygons, speci. The structure of a clip polygon should be restored efficiently after each clipping operation, to enable efficient execution of the whole clipping process. An algorithm that clips a polygon is rather complex. 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. Polygon clipping and filling computer science department. Nonconvex polygon polygon clipping its the process of finding the exact part of a polygon lying inside the view volume window must be convex.
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