Line clipping algorithms cohen sutherland line clipping algorithm 2. Computational algorithms for increased control of depth. This document is highly rated by computer science engineering cse students and has been viewed 677 times. Mathematically, clipping can be described using the terminology of constructive geometry. Line and polygon clipping brute force analytic solution. The two dimensional viewing pipeline clipping window the part of two dimensional scene that it to be displayed viewport window where data from clipping window will be displayed mapping between these two called 2d viewing transformation clipping window viewport. Some improvements to a parametric line clipping algorithm. Gate preparation, nptel video lecture dvd, computerscienceandengineering, computergraphics, threedimensionalviewing, computer graphics, survey of computer.
Apr, 2019 the two dimensional viewing is a transformation process of real world object into position point which is relative to the viewing volume, especially, the points behind the viewer. Explain sutherland hodgeman algorithm for polygon clipping. Figure 84 a viewingcoordinate frame is moved into coincidence with the world coordinate frame by a applying a translation matrix t to move the viewing origin to the world origin, then b applying a rotation matrix r to align the axes of the two systems. A set of unit vectors that define the viewing coordinate system is obtained by. Clipping, in the context of computer graphics, is a method to selectively enable or disable rendering operations within a defined region of interest. Overview two dimensional viewing pipeline the clipping window normalizations and viewport transformations. Gate preparation, nptel video lecture dvd, computerscienceandengineering, computergraphics, twodimensionalviewingfunctions, computer graphics, survey of. Operators were added to this system which allow the user to create 2d transformation matrices that perform the following transformations. Clipping there is something missing between projection and viewing. Viewing windows are always chosen however, as convex sets in a ilibert space. Construct the scene in world coordinate using the output primitives. Opengl two dimensional viewing program example 248 85 clipping algorithms 250 86 two dimensional point clipping 250 87 two dimensional line clipping 251 cohensutherland line clipping 252 liangbarsky line clipping 257 nichollleenicholl line clipping 260 line clipping using nonrectangular polygon clip windows 262. T 81 where t is the translation matrix that takes the viewing origin point p 0 to the world origin, and r is the rotation matrix that aligns the axes of the two.
Cohen sutherland line clipping cohen sutherland line clipping produce a region code for each endpoint of the line segment, e. What are basic geometric transformations applied to twodimensional objects. Explain the disadvantage of it and how to rectify this disadvantage. Opengl 3d viewing functions opengl perspectiveprojection function the projection reference point is the viewingcoordinate origin the near clipping plane is the view plane symmetric. Outline opengl 2d viewing types of clipping algorithms 2d point clipping. You can translate a point in 2d by adding translation coordinate t x, t y to the original coordinate x, y to get the new coordinate x. Viewing computer engineering kocaeli university model model model m1 m2 m3 3d world scene 3d view scene v p clip normalize 2d3d device scene 2d image projection rasterization modeling transformations viewing transformations mcs wcs vcs ndcs dcs scs viewing pipeline revisited model world model coordinates to world coordinates. The equations of the four bounding planes of the right pyramid are. Typically, any line or part thereof which is outside of the viewing area is removed. Another simple but faster method for 2d line clipping. Opengl twodimensional viewing program example 248 85 clipping algorithms 250 86 twodimensional point clipping 250 87 twodimensional line clipping 251 cohensutherland line clipping 252 liangbarsky line clipping 257 nichollleenicholl line clipping 260 line clipping using nonrectangular polygon clip windows 262. Clipping is a process that subdivides each element of a picture to be displayed into its visible and invisible parts, thus allowing us to discard the invisible parts of the picture. The pair t x, t y is called the translation vector or shift vector. Oct 09, 2018 cgmm lecture 21 cohen sutherland line clipping algorithm part 1 hindienglish what is the clipping.
If both c1 and c2 are 0000s, the line segment is within the clip window. Two dimensional geometric trarusformations basic transformations. A clipping algorithm is derived and both two and threedimensional. Clipping can be done either in threedimensional space, or in image space. T 81 where t is the translation matrix that takes the viewing origin point p. Apart from clipping to the view volume, clipping is a basic operation in many other algorithms. Two dimensional geometric transformations matrix representations and homogeneous coordinates, composite transformations.
This algorithm uses the clipping window as shown in the following figure. For a three dimensional scene it is called a clipping region. Viewing transformation in 2d a scene in worldcoordinates. This is achieved by processing all polygon vertices against each clip rectangle boundary in turn. Clippingview window the rectangle defining the part of the world we wish to display. Line clipping against non rectangular clip windows 4. Computer graphics two dimensional viewing functions exam. Jul 22, 2015 page 1 computer graphics window to viewport transformations window to viewport transformations page 2 computer graphics window to viewport transformations window to viewport transformations two dimensional viewing composite transformation the viewing pipeline viewing effects 2 viewing coordinate reference frame workstation transformation clipping operations line.
Viewing coordinates transform viewing coordinates to normalized coordinates nc map normalized coordinates to device coordinates dc figure 63 twodimensional viewingtransformation pipeline. A clipping algorithm is a procedure for eliminating a portion of a. The viewing space is divided into nine encoded regions as shown below. Viewing transformation in 2d x world y world x v i ew y v i ew world and viewing coordinates normalized device coordinates 1 1 x view y iv ew clipping device coordinates. A mathematical description of a two or three dimensional \scene and a viewing position. Two dimensional viewing viewing pipeline, viewing coordinate reference frame. Reflection and shear raster method for transformation. The ability to perform transformations on objects in an image is an important feature of a graphics system. All parts lie outside the viewport are clipped, and contents of the viewport are transferred to device coordinates. Nov 22, 2016 apr 29, 2020 threedimensional viewing.
In twodimensional clipping, if the clipping object is an axisaligned rectangular parallelogram, it is often called the clipping window or clip window. A polygon can be clipped by processing its boundary as a whole against each window edge. Rectangle specified in world coordinates displayscreendevice coordinate system. Mcqs for computer graphics and gaming unit3 and unit4 1. Page 1 computer graphics window to viewport transformations window to viewport transformations page 2 computer graphics window to viewport transformations window to viewport transformations two dimensional viewing composite transformation the viewing pipeline viewing effects 2 viewing coordinate reference frame workstation. For a threedimensional scene it is called a clipping region. Topics viewing transformation pipeline in 2d line and polygon clipping brute force analytic solution cohensutherland line clipping algorithm cyrusbeck line clipping algorithm. In 2d, the clipping process can be applied to a variety of graphics primitives such as points, lines, polygons and curves. Clipping is a computer graphics process to remove the lines, objects, or line segments, all of which are outside the viewing pane. Viewing coordinates vc transform viewing coordinates to normalized coordinates nc map normalized coordinates to device coordinates dc figure 63 two dimensional viewing transformation pipeline. Specifying the viewing coordinate system view reference point we first pick a world coordinate position called view reference point origin of our viewing coordinate system. Cgmm lecture 21 cohen sutherland line clipping algorithm. The primary use of clipping in computer graphics is to remove objects, lines, or line segments that are outside the viewing pane.
Given a set of 2d lines or polygons and a window, clip the lines or polygons to their. Clipping is performed with respect to a clipping boundary, which may be a convex. Rotation matrix representation and homogeneous coordinates composite transformation other transformations. Size of clipping window position orientation window aperture of the camera. Transform descriptions in world coordinates to viewing coordinates. Cohensutherland algorithm and, if necessary, clip them against. A clipping algorithm is a procedure for eliminating a portion of a picture outside of a specified region. Liangbarsky line clipping the parameters of the intersections of s 1 s 2 with the starting edge are referred as u1, u1 u1 maxu1, u1, 0 the nearest clipping point to s 2 the parameters of the intersections of s 1 s 2 with two ending edges are referred as u2,u2 u2 minu2, u2, 1 the nearest clipping point to s 1. Can the boundary of two convex shapes intersect more than twice. In this paper, we concentrate on clipping methods for polygons, clipping them against planes. Obtain a particular orientation for the window by set up a two dimensional viewing coordinate system in the world coordinate, and define a window in the viewing coordinate system. Viewing coordinates transform viewing coordinates to normalized coordinates nc map normalized coordinates to device coordinates dc figure 63 two dimensional viewing transformation pipeline.
Much like what we see in real life through asmall window or the view finder of a camera. Viewing coordinates vc transform viewing coordinates to normalized coordinates nc map normalized coordinates to device coordinates dc figure 63 twodimensional viewingtransformation pipeline. Viewing transformation pipeline in 2d line and polygon clipping. Explain sutherland hodgeman polygon clipping algorithm. The viewing transformation is insensitive to the position of points relative to the viewing volume. Two dimensional viewing functions and clipping cs116a chris pollett nov. The basic problem to be addressed may roughly be stated as. Define window, viewport, user and screen coordinate. Figure 62 a clipping window and associated viewport, specified as rectangles aligned with the coordinate axes.
Usually a clipping window is a rectangle in standard position, although we could use any shape for a clipping application. What are basic geometric transformations applied to two dimensional objects. Chapter 5 twodimensional viewing operations viewing. Figure 84 a viewing coordinate frame is moved into coincidence with the world coordinate frame by a applying a translation matrix t to move the viewing origin to the world origin, then b applying a rotation matrix r to align the axes of the two systems. A marks 1 unit 4 28 the first viewing parameter we must consider is the. It is a formal mechanism for displaying viewsof a picture on an output device. By changing clipping window size or position, zooming, overview, or panning effects produced by moving a fixed size window across the various object in a scene can be achieved twodimensional viewing pipeline bhargav rajyagor bic. Two dimensional viewing pipeline the clipping window normalizations and viewport transformations opengl 2d viewing functions clipping. A rendering algorithm only draws pixels in the intersection between the clip region and the scene model. Twodimensional viewing and clipping viewing transformation and window to.
By changing the viewport position allows for viewing objects at different locations on the display device. Two dimensional raster algorithms in this and subsequent chapters we will build up techniques for creating color images of complex three dimensional environments using full color frame bu. Enhanced stereo 3d algorithms conventional computational techniques utilized in stereopsis display generation rely on symmetric. In computer graphics, line clipping is the process of removing lines or portions of lines outside an area of interest. Clipping computer graphics c version computer science engineering cse notes edurev is made by best teachers of computer science engineering cse. Implementation of two new computational techniques, an. A graphicspackage allows the user to specifya which part of the defined picture is to be displayed. The two dimensional viewing is a transformation process of real world object into position point which is relative to the viewing volume, especially, the points behind the viewer. By changing clipping window size or position, zooming, overview, or panning effects produced by moving a fixed size window across the various object in a scene can be achieved two dimensional viewing pipeline bhargav rajyagor bic.
By observing the original smiley face closely, we can see that there are two blue. Cgmm lecture 21 cohen sutherland line clipping algorithm part 1 hindienglish what is the clipping. Before projecting, we need to eliminate the portion of scene that is outside the viewing frustum x y z image plane near far c lip ed n need to clip objects to the frustum truncated pyramid now in a canonical position but it still seems kind of tricky. Point clipping given a clipping rectangle in standard position, we save a two dimensional point p x, y for display if if any of these inequalities is not satisfied, the point is clipped i. Gate preparation, nptel video lecture dvd, computerscience and engineering, computergraphics, two dimensional viewing functions, computer graphics, survey of.
For threedimensional clipping, lines are clipped against a viewing pyramid. In this case, the coordinate system is transformed to a rightpyramid coordinate system where the viewing volume is a right pyramid, as shown in figure 12a. A translation moves an object to a different position on the screen. Such an algorithm is most often used as final portion of viewing pipeline before image displayed to device. Mcqs for computer graphics and gaming unit3 and unit4.
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