Lecture 7: Objects and Interaction 1  Principles of Interactive Graphics  CMSCD2012  Dr David England, Room 718,  ex 2271  / /  Web page includes: announcements, handouts, web links, reading hints, frequently asked questions

Lecture 7: Objects and Interaction 2 Courseworks  Coursework 1 admin  Hand in your design and code to the Campus Office  Do your demo between 3 and 5pm today  If you cannot do the demo just hand in what you have and ask me about things you did not understand  Coursework 2  Task will be to design and create a 2D controllers for a 3D object  part 1: design and implement simple buttons to control the attributes of the 3D object  part 2: design and implement scrollbars to control the attributes  Optional: Exploit OO techniques to manage design and code

Lecture 7: Objects and Interaction 3 Today’s Lecture: 3D concepts  Object Oriented Design, (OOD) and Computer Graphics  How OOD has enabled the Graphical User Interface revolution  Designing your own objects in OOD  Background for coursework 2

Lecture 7: Objects and Interaction 4 Object Oriented Design  In CY2001 you will have come across concepts such as  Defining Classes and Objects  Encapsulation (private variables and functions for classes)  Polymorphism - functions with the same name but different parameters  Moving from OO design to OO Programming  Abstraction (to different levels) is the main technique of problem solving in Computer Science  OOD works by abstracting out the essential classes of objects in a problem, identifying their attributes and their functionality

Lecture 7: Objects and Interaction 5 Object Oriented Design...  “… the hype surrounding OOSD looks more like reality and that adopting OOSD may indeed be worth the related time, effort and cost.” R Johnson CACM October 2000  OOD and OOP help control the complexity of larger systems development  In your own programs you will have seen the Display() function grow in size with the complexity of the graphical scene  How could you have use OOD and OOP to control and manage this growth? (we’ll come back to this)

Lecture 7: Objects and Interaction 6 OO Graphical User Interfaces - GUI  Smalltalk 80 was the first complete object-oriented programming environment.  Everything in Smalltalk-80 is an object, from integers upwards  The designers chose to split an application up into three parts  The View - the graphical part  The Controller - the input handling part  The Model - the logical part of the application (text handling, database handling or whatever)  Objects in the Controller (e.g. a menu handler) send messages to the Model to do some calculation, which then sends a message to update the View.

Lecture 7: Objects and Interaction 7 OO Graphical User Interfaces ….  The same model - MVC - can be seen in the design and implementation of current GUI toolkits  Java Swing  Microsoft Foundation Classes (MFC)  Swing and MFC put the Controller and View together  MFC has a Document/View structure  Separating the Document and View parts of an application mean that different teams can work on the different parts  The GUI or View might require 50 to 90% of the development effort of a whole project!

Lecture 7: Objects and Interaction 8 Designing your own Graphical Objects  OpenGL is designed around the idea of sending commands down a graphical pipeline  This maybe a good way of developing graphically intense programs such as games  While this reflects the underlying hardware it is not always the best way to program all graphical applications  In your coursework you may have split up the display() function to call other functions to draw the parts of the scene  For example, a dial() function which could draw a new dial in a different location

Lecture 7: Objects and Interaction 9 Designing your own Graphical Objects...  The dial() function could be extended to further parameters such as  Colour of border and background  Radius  Range of dial readings  Division of dial readings  Colour and size of value indicator  Font of dial readings  and so on

Lecture 7: Objects and Interaction 10 Designing your own Graphical Objects...  Or we could take advantage of OOD and design a Dial Class comprising  Private attribute of the attributes listed above  An attribute for the current_pointer value  Constructors to create a new Dial object  A draw function (hiding the OpenGL implementation)  An update function to change current_pointer and redraw the pointer  The rest of the program would then only communicate with the dial via speed_dial.setCurrentPointer(int value);

Lecture 7: Objects and Interaction 11 Designing your own Graphical Objects...  Think for a moment of what other objects in your scene you could create classes for  What would be their attributes?  What methods would be needed?  What attributes would be exposed to the rest of the program to update your object?  For example  Dials and other instruments, radar displays, indicator lamps, external scenery  Kitchen objects as part of a library for a kitchen design program

Lecture 7: Objects and Interaction 12 Resources for Coursework 2  Use glutSolidCube(), or other GLUT convenience routines, to create a 3D object  The left mouse button generates the input events when over a button or scrollbar area - see the functions mouse() and motion() in inputevents.cpp  You have to manage the state between the different mouse events in a button or scrollbar  You could exploit OOD/OOP in reusing buttons and scrollbars

Lecture 7: Objects and Interaction 13 Next Week  We will start to look in more detail at some of the principles of 3D graphics