Lecture 11: Exam Revision 1  Principles of Interactive Graphics  CMSCD2012  Dr David England, Room 718,  ex 2271  Coursework deadline extended to Tuesday 4th Dec  No demo session - me your working code or submit it on disk  No compliable code submitted means no marks for the demo

Lecture 11: Exam Revision 2 This Week Exam Revision  Aims and objectives of the module  Graphics Hardware  Interactive graphics application framework  Graphics context  Transforms  Texture mapping  Lighting, Shading and Materials  Sense of Depth

Lecture 11: Exam Revision 3 Learning outcomes  Learning outcomes of the module. You should be able to: 1 Identify the hardware and software needed for Computer Graphics applications 2 Solve problems in 2D graphics and interaction 3 Develop applications using 2D graphics and 2D input devices 4 Explain the principles behind 2D and 3D graphics  The exam tests 1, 2 and 4 (and OpenGL concepts)  The coursework tested 2, 3 and 4

Lecture 11: Exam Revision 4 Graphics Hardware  In lecture 4 we looked at Graphics hardware and the handout from PCW on PC graphics cards  We looked at different display devices and how they fitted in with the display architecture of a machine  We saw how graphics performance could be improved by various techniques  We looked at the basic features of input devices for 2D and 3D graphics  We looked at the features that make a device suitable for interaction

Lecture 11: Exam Revision 5 Handling Events 1  In Lecture 5 we looked at event handling in OpenGL  Every interactive graphics program has the same model Initialise the application data and graphics environment Create the contents of the display Paint the contents of the display on a window Set-up functions to handle input events Start an infinite loop to handle input events  This is event-driven programming  I posed some questions about handling events for some items...

Lecture 11: Exam Revision 6 Handling Events 2  A scrollbar, e.g.  e.g. top arrow box  Click Left mouse button  Show arrow box depressed  Move client window up one unit  Restore arrow box  e.g. Central bubble  Press left mouse button down  Drag mouse  Move client window in direction of mouse  Release mouse  The movement of the client may vary between applications

Lecture 11: Exam Revision 7 Handling Events 3  A pop-up menu  Press right/left mouse button (left for MS Start Menu)  Show top-level menu  Loop 1: Drag mouse cursor over item  Highlight item  If item is sub-menu show sub-menu  Continue loop 1:  Press mouse button over item - do menu action  Press mouse button not over item - hide all menus

Lecture 11: Exam Revision 8 Handling Events and Application Frameworks  In Lecture 7 we also saw how input handling fits in with Object-Oriented application frameworks  For example:  Model-View controller in Smalltalk-80  Document/View structure in Java Swing and Microsoft Foundation Classes  We also saw how graphical components could be designed as classes and objects  The display and input handling of a class is built into the class itself  A limited interface is exposed to the rest of the program

Lecture 11: Exam Revision 9 3D graphics: Transforms  We started by looking at the basic transform operations  Translation in the X, Y and Z planes  Rotation about the X, Y and Z axes  Scaling in X, Y and Z  We discussed the concept of Graphics Context and saw that transformations are cumulative unless we change the context  E.g. by loading the Identity Matrix - glLoadIdentity()  Or (later on) by saving and then restoring the transformation context with glPushMatrix() and glPopMatrix()  Rendering continues in the current graphics context unless the programmer changes it

Lecture 11: Exam Revision 10 Texture Mapping  In Lecture 8 we looked at texture mapping  We saw how texture objects could be created in a program or read from a file  Textures can then be applied to an object to add detail to the scene without using extra polygons  Texturing has to be enabled before texture objects can be used  Texture coordinates go from 0.0, 1.0 in X and 0.0, 1.0 in Y  We set different coordinates so we can match all, part or repeated copies of the texture across a set of vertices in a polygon  We can also have the texture affected by materials and lighting

Lecture 11: Exam Revision 11 Lighting, Shading and Materials  We saw in lecture 9 how lighting and shading can be controlled to give a sense of depth and position  Shading can be flat or smooth across a polygon to give more realistic smooth objects  We can enable lights in a scene and control their properties e.g.  Colour or brightness  Position of point source lights  We can also control how an object responds to lighting by setting material values to make objects dull or shiny to match real-world surface reflections and colours  Remember: Context and lighting

Lecture 11: Exam Revision 12 Sense of depth  OpenGL gives a sense of depth via  Lighting and shading (last section)  Perspective gluPerspective()  This set the angle of view  the aspect ration of the scene  The front and back viewable planes  enabling Depth Testing  Depth testing switches on hidden line and surface removal  Without this all parts of an object would be visible

Lecture 11: Exam Revision 13 Answer to last tutorial question  “Modify the rotate operation so that the scene rotates around the current viewpoint and not the origin”  Create a camera object to store the current position in x,y and z and the current rotations about x,y, and z axes  Take user input to move around the scene  In the display function: translate and rotate using the current camera values  Then redraw the whole scene  See Chapter 19 Simple Tank in OpenGL Superbible - VC++ workspace is in L:\CD2012

Lecture 11: Exam Revision 14 Finally  There are no trick questions  Please read the exam questions carefully  Plan out your answer  Don’t do a brain dump of lecture notes/reading based on misreading questions  Good Luck  Any final questions ?