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GT LCC 6310 - A Man‐Machine Graphical Communication System

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Presented by Jayraj JogA Man‐Machine GraphicalA ManMachine Graphical Communication Systemy Developed by Ivan Sutherland at MIT in the 1960sy Introduced as conversation between humans and computersAn Example of Sketchpad in Usehttp://www.youtube.com/watch?v=mOZqRJzE8xgBasic Elements Observedy Use of sub‐pictures: Pictures once drawn can be used to make more complex pictures, which in turn can be used to draw more complex picturesused to draw more complex picturesy Constraints: Vertical, horizontal, parallel, perpendicular attach points upright symbols relate perpendicular, attach points, upright symbols, relate symbolsy Definition copying: Combination of operationspy g pIntended Uses of SketchpadyLibrary of drawingsyScientific and engineering visualizationyScientific and engineering visualizationyCircuit design and simulationyRepetitive drawings (sounds similar to first point)first point)Architecture –Ring Structurey Elements stored in blocks: strings of pointers to elementsyElements found by accessing the block to which they yElements found by accessing the block to which they belong and following the linksy Formed a circular linked list of elementsy Operations on these blocks were elementary (all done using MACRO instructions):yInsertionyInsertiony Deletiony SortinggThe Light Pen (Lightsaber? PenThe Light Pen (Lightsaber? Pen mightier than sword et c.)y Light pen must be “inked up” to establish tracking, and moved really fast across screen to end trackingU f h hh dib hi f yUse of phrases throughout text to describe things for which we have words today –eg. “Display spot” for “pixel”pixely Objects within 1/8thinch of pen center were considered; established an area of influence for light gpeny Bringing pen close to an element gives it a pseudo‐iipositionDisplay Generationy Use of TX‐2 computer; displays 100K “display spots”/second (a computer with 64k memory, 36‐bit word‐size)wordsize)y Digits and text, used for legends, typed in by keyboard. Accommodated up to 36 characters/liney Buffering and interlacing done for smoother displayy Each display spot described by 36 (20 for co‐ordinates, 16 for address in ring structure) bits in memory16 for address in ring structure) bits in memoryy Allowed magnification of up to 2000 timesy This involves solving problems such asg pEdge Detectiony Knowing what is to be displayedy Knowing how much is to be displayedy Considered a non‐trivial problemUse of Recursive Functionsy A Good Idea (capitalized on purpose) because it allowed use of generic functions over and ov er to do:Ei f I Sbi ihi byExpansion of Instances: Sub‐pictures within sub‐pictures within sub‐pictures ad infinitumyRecursive DeletionRecursive Deletiony Recursiv e MergingBuilding a Drawingy Involves recursive use of picture parts and constraintsy Actually copying a definition picture is slightly li d (b d dd)complicated (by modern standards)y Requires “designated attachers (not a word)” that are part of the objectpart of the objecty Instances are different from definition pictures: all the parts of an instance are drawn tog ether and get parts of an instance are drawn tog ether and get deleted togetherHow Constraints are SatisfiedyAlso entered into system in the form of a blocky Consists of a subroutine that finds how much error enters the system (there’s always an error) because of applying the the system (there s always an error) because of applying the constrainty This can be done by one‐pass method, or “reliable but slow method of relaxation”method of relaxationy One‐pass method: the short storyy Find drawing variable with fewest (or very few) constraints d land evaluate ity Plug value into variable with next fewest numbers and evaluate ity RepeatExamples of Sketchpad usageExamples of Sketchpad usage during testingy Patternsy Linkagesy Dimension Linesy Bridgesy Electrical Circuit Diagramsy Artistic DrawingsOne Thesis, Many Ideasy Graphical User Interfacey Graphicsy Computer Assisted Drawing/Computer Aided DrawingObjOi d PiyObject‐Oriented ProgrammingSketchpad Demo Videosy http://www.youtube.com/watch?v=mOZqRJzE8xgy http://www.youtube.com/watch?v=USyoT_Ha_bA&feldature=relatedy http://www.youtube.com/watch?v=BKM3CmRqK2o&feature


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