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Lecture 5 Other Output Models Structured Graphics Object Oriented Techniques Brad Myers 05 830 Advanced User Interface Software 1 Structured Graphics Saves a list of all the graphical objects Edit the screen by editing the saved list Also called display list or retained object model Provided by many toolkits and graphics packages early vector displays CORE 1977 GKS 1985 PHIGS 1988 Optional in InterViews CLIM etc Required in Amulet Garnet Rendezvous etc 2 Structured Graphics cont Advantages Simpler to program with don t call draw and erase Automatic refresh of windows when uncovered etc Automatic redisplay of objects when change and also of other overlapping objects 3 Structured Graphics Can Support Ability to support high level behaviors like move grow cut copy paste etc high level widgets like selection handles constraints among objects automatic layout grouping Groups in Garnet automatic PostScript printing tutors and monitors external scripting 4 Structured Graphics Disadvantages Disadvantages Significant space penalties objects take up to 1000 bytes each imagine a scene with 40 000 dots 200x200 fat bits Time penalties Redisplay doesn t take advantage of special properties of data regularity non overlapping 5 Redisplay Algorithms Redisplay everything each time Most appropriate for small numbers of objects and if drawing is really quick compared to computation Used on the Macintosh and many others Used by Amulet Used by homework 2 May add clipping region and or double buffering 6 Redisplay only the affected areas of the screen Requires computing what areas are affected Garnet 1 2 3 4 5 keep track of objects that change any interesting slot compute the bounding box of all these changed objects in their old and new locations assert this as the clipping region must not self intersect Garnet uses 2 regions erase the area go through objects from top to bottom back to front draw those which overlap the bounding box for step 4 goes through all top level aggregates and any children of the aggregates that intersect recursively Other techniques quad trees 7 Issue Anti Aliasing and special effects Drop shadows highlights other special effects Can t assume clipping regions will work Can draw outside of the bounding boxes Mac OS X uses anti aliasing and seems to redraw lots of windows 8 Optimizing Redraw Special Fast redraws additions in Garnet not in Amulet declared by the programmer objects drawn with XOR on top of other objects those that have a solid color behind them nothing in front so can be erased with a rectangle or by redrawing with the background color When change have to be erased using old values No bounding boxes no intersections etc Virtual aggregates only pretend to allocate storage for elements provide table and arbitrary layouts 9 Optimizing Redraw Glyphs in InterViews Calder P R and Linton M A Glyphs Flyweight Objects for User Interfaces in Proceedings UIST 90 ACM SIGGRAPH Symposium on User Interface Software and Technology 1990 Snowbird Utah pp 92 101 Don t include position information etc so very small Much of the layout retained by the aggregate computed as needed Object can be reused in many places e g the letter a Used for a text editor Issue why is location special What about red vs blue a s 10 Object Oriented Techniques Motivation Became popular along with GUIs Direct Manipulation Icons graphics seem like objects have internal state persistance OO was originally developed SmallTalk and became popular C mostly due to GUIs 11 Object Oriented As a UI technique Same as GUI Direct Manipulation icons graphical objects widgets Here as a programming paradigm often in a language A form of data abstraction Classes describe the basic structure of the data Also the methods that can be called Usually no direct access to the data only the methods 12 OO Create instances of the classes Inheritance create a new class like the superclass local copy of data may also be class data shares all methods by default has all the same methods and data can add new data and methods and re program inherited methods Example graphical object draw circle draw 13 OO New style of programming thinking about the problem Many books about how to do it right OO design getting the classes and protocols right So subclasses don t have extra wasted data space Methods make sense to all sub classes So external classes don t need to know inside description Also OO databases etc Implementation object in memory starts with pointer to table of methods etc lots of tricks and extra declarations in C etc to avoid overhead of lookups virtual pure virtual 14 Multiple inheritance Class has multiple parent classes Combine all the methods and data of all Special rules for when conflict same method same name of data with different types etc Example circle inherits from graphical object and moveable object Complex so often not used even when available Amulet uses constraints to provide flexible copying of values instead Java etc use interfaces No inheritance of implementations but ability to have arbitrary mix ins 15 Prototype Instance model Instead of the class instance model All objects are instances Can use any object as a prototype for other objects Inherits all slots it doesn t override instance variables member variables fields attributes Methods are just a value in a slot Dynamic changing of methods Easy to implement using structures Usually changing prototype data also changes all instances that do not override it 16 Prototype Instance model 17 Prototype Instance model May provide adding and removing of slots dynamically to any instance Simpler model easy to implement But much less efficient Can t usually compile slot accesses into structure access may need a search Type checking on slots Methods looked up at run time Space for names of slots extra pointers etc 18 Examples of OO Systems OO in SmallTalk First pure example Everything is an object numbers strings etc Single inheritance Methods dispatched on a single parameter 3 4 5 different from 4 5 3 Dynamic method lookup at run time Message not understood Smalltalk 72 had strange syntax with special characters Whole environment windows browsers MVC etc 19 Examples of OO Systems OO in C Numbers strings etc not objects Lots of mess to make it fit with C Statically compile time determine types methods Originally a pre processor new syntax Multiple inheritance 20 Examples of OO Systems OO in CLOS Common Lisp Object System Add on to language Special feature method


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