1. 30/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)1 CSC345: Advanced Graphics & Virtual Environments Lecture 1: Introduction to OpenGL (1) Patrick Olivier p.l.olivier@ncl.ac.uk 2 nd floor in the Devonshire Building

2. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)2 Course structure  Introduction to OpenGL  Visual appearance (fogging & transparency)  Discrete Techniques (aliasing & textures)  Advanced lighting & shading (shadows & reflections)  Curves & curved surfaces  Solid object modelling  Visualisation  Procedural modelling  Acceleration algorithms  Intersection and collision detection  Non-photorealistic rendering  Virtual environments

3. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)3 Required reading (1) Edward Angel: “Interactive Computer Graphics: A Top-Down Approach Using OpenGL” 3 rd Edition Addison Wesley, 2002 Required for theory

4. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)4 Required reading (2)  Put image here Edward Angel: “OpenGL: A Primer” 2 nd Edition Addison Wesley, 2004 Compulsory for practicals

5. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)5 Extra reading…  Put image here Tomas Akeine-Möller & Eric Haines: “Real-time Rendering” 2 nd Edition AK Peters, 2002 Advanced topics & for serious graphics types

6. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)6 Extra reading…  Put image here “OpenGL Programming Guide: The Official Guide to Learning OpenGL” 4 th Edition Addison Wesley, 2004 Old version online: see module webpages

7. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)7 Practical (programming) schedule… 1. Two-dimensional programming & C (OpenGL primer: ch. 2) 2. Two-dimensional programming & C (OpenGL primer: ch. 2)  Exercise 1 (worth 3% is due: 13 th February) 3. Interaction & animation (OpenGL primer: ch. 3) 4. Basic three-dimensional programming (OpenGL primer: ch. 4) 5. Transformations (OpenGL primer: ch. 5)  Exercise 2 (worth 3% is due: 6 th March) 6. Lights & materials (OpenGL primer: ch. 6) 7. Images (OpenGL primer: ch. 7) 8. Texture mapping (OpenGL primer: ch. 8)  Exercise 3 (worth 4% is due: 27 th March) 9. Curves & surfaces (OpenGL primer: ch. 9)  Exercise 4 (worth 15% is due: 12 th May)  Exam is worth 80% date to be confirmed

8. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)8 OpenGL library  OpenGL core library OpenGL32 on Windows GL on most unix/linux systems (libGL.a)  OpenGL Utility Library (GLU) Provides functionality in OpenGL core but avoids having to rewrite code  Links with window system GLX for X window systems WGL for Windows AGL for Macintosh

9. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)9 GLUT library  OpenGL Utility Toolkit (GLUT)  Provides functionality common to all window systems open a window get input from mouse and keyboard menus event-driven  Code is portable but GLUT lacks functionality of a good toolkit for a specific platform e.g. no slide bars

10. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)10 OpenGL architecture Immediate Mode Display List Polynomial Evaluator Per Vertex Operations & Primitive Assembly Rasterization Per Fragment Operations Texture Memor y CPU Pixel Operations Frame Buffer geometry pipeline

11. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)11 OpenGL functions  Primitives Points Line Segments Polygons  Attributes  Transformations Viewing Modeling  Control (GLUT)  Input (GLUT)  Query

12. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)12 OpenGL state  OpenGL is a state machine  OpenGL functions are of two types Primitive generating  Can cause output if primitive is visible  How vertices are processed and appearance of primitive are controlled by the state State changing  Transformation functions  Attribute functions

13. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)13  OpenGL is not object oriented so that there are multiple functions for a given logical function glVertex3f glVertex2i glVertex3dv  Underlying storage mode is the same  Function format: OpenGL function format function name glVertex3f(x,y,z) belongs to GL library x,y,z are floats dimensions glVertex3fv(p) p is a pointer to an array

14. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)14 OpenGL #defines  Most constants are defined in the include files gl.h, glu.h and glut.h Note #include should automatically include the others Examples:  glBegin(GL_POLYGON)  glClear(GL_COLOR_BUFFER_BIT)  include files also define OpenGL data types: GLfloat, GLdouble,….

15. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)15 A simple program: simple.c #include void mydisplay(){ glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POLYGON); glVertex2f(-0.5, -0.5); glVertex2f(-0.5, 0.5); glVertex2f(0.5, 0.5); glVertex2f(0.5, -0.5); glEnd(); glFlush(); } int main(int argc, char** argv){ glutCreateWindow("simple"); glutDisplayFunc(mydisplay); glutMainLoop(); }

16. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)16 Event loop & defaults  program defines display callback function named mydisplay every glut program must have a display callback display callback is executed whenever OpenGL decides the display must be refreshed, (e.g the window is opened) main function end by entering an event loop  simple.c is too simple  makes heavy use of state variable defaults viewing / colours / window parameters  next version makes defaults more explicit

17. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)17 Compilation  Unix/linux include files usually in …/include/GL compile with –lglut –lglu –lgl loader flags may have to add –L flag for X libraries make file provided on module webpage  Windows (Visual Studio) get glut.h, glut32.lib and glut32.dll from web create a console application add opengl32.lib, glut32.lib, glut32.lib to project settings (under link tab)

18. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)18 Program structure  most OpenGL programs have same structure: main()  defines the callback functions  opens one or more windows with the required properties  enters event loop (last executable statement) init()  sets the state variables (viewing / attributes) callbacks…  display function  input and window functions  rewrite simple.c that sets colour, view & window…

19. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)19 #include int main(int argc, char** argv) { glutInit(&argc,argv); glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB); glutInitWindowSize(500,500); glutInitWindowPosition(0,0); glutCreateWindow("simple"); glutDisplayFunc(mydisplay); init(); glutMainLoop(); } main.c …define window size …define window position …set OpenGL state …enter event loop

20. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)20 GLUT functions  glutInit allows application to get command line arguments and initializes system  gluInitDisplayMode requests properties for the window (the rendering context) RGB color single buffering properties logically ORed together  glutWindowSize in pixels  glutWindowPosition from top-left corner of display  glutCreateWindow create window with title “simple”  glutDisplayFunc display callback  glutMainLoop enter infinite event loop

21. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)21 init.c void init() { glClearColor (0.0, 0.0, 0.0, 1.0); /* first 3 values = black, final = opaque */ glColor3f(1.0, 1.0, 1.0); /* set current draw colour to white */ glMatrixMode (GL_PROJECTION); glLoadIdentity (); glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0); /* bounds of the view volume */ }

22. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)22 Coordinate systems & cameras  units of glVertex in object coordinates  viewing specifications also in object coordinates  OpenGL converts to camera (eye) coordinates and later to screen coordinates  OpenGL puts camera at the origin pointing in -z direction direction  The default viewing volume is a box centered at the origin of length 2

23. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)23 Transformations and viewing  In OpenGL, projection is carried out by a projection matrix (transformation)  There is only one set of transformation functions so we must set the matrix mode first glMatrixMode (GL_PROJECTION)  Transformation functions are incremental so: we start with an identity matrix alter it with projection matrix that gives the view volume glLoadIdentity(); glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);

24. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)24 2-D and 3-D viewing  The near & far distances are measured from the camera, in: glOrtho(left,right,bottom,top,near,far)  Two-dimensional vertex commands place all vertices in the plane z=0  If the application is in two dimensions, we can use the function: gluOrtho2D(left,right,bottom,top)  In two dimensions, the view or clipping volume becomes a clipping window

25. 31/1/2006Based on: Angel (4th Edition) & Akeine-Möller & Haines (2nd Edition)25 mydisplay.c void mydisplay() { glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POLYGON); glVertex2f(-0.5, -0.5); glVertex2f(-0.5, 0.5); glVertex2f(0.5, 0.5); glVertex2f(0.5, -0.5); glEnd(); glFlush(); }