OpenGL Libraries and Midterm Review: Understanding Rendering Pipeline and Event-Driven Programming

1. Lecture 7 Midterm Review

2. OpenGL Libraries • gl: Basic OpenGL library, e.g. primitives. • glu: OpenGL Utility library, a set of functions to create texture mipmaps from a base image, draw quadric surfaces and NURBS. • glut: OpenGL Utility Toolkit library. A system independent windowing system. • Hierarchical view of libraries: • http://www.nigels.com/glt/doc/gl_8h.html

3. Mesa 3D • Mesa 3D is a free/open source implementation of OpenGL. • This is a good source if you plan to see the implementation details of a function. • http://www.mesa3d.org

4. Rendering Pipeline

5. Rendering Pipeline • Evaluators • Deriving vertices from basis functions • Vertices can be used to represent a surface • Per-Vertex Operations • Converts vertices into primitives i.e. line, polygon, etc. • Does mathematical operations, i.e. transformation, rotation, projection, etc.

6. Rendering Pipeline • Rasterization: Conversion of geometric and pixel data into fragments. • Each fragment corresponds to a pixel in frame buffer. • When creating models, many parameters have to be considered, e.g. shading model, color, point size, etc.

7. Fragment Operations • Before a fragment be placed in frame buffer, the following can be controlled: • Texture Mapping • Fog calculations • Alpha Test, depth buffer test • Blending, masking, etc.

8. GLUT Window Initialization • What is Buffer? • Clearing the Window • glClearColor(R, G, B, A) • glClearColor(GL_COLOR_BUFFER_BIT) • glClearDepth() • glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

9. OpenGL Buffers

10. Event Driven Programming • Definition. A programming where the primary activity is reaction to the receipt of event. • Applications: GUI, HCI • Ingredients: • Events: Can be from any source, human input, e.g. mouse or other sensors. • Event Dispatcher: Assigns events to event handlers. • Event Handler

11. Event Processing in GLUT • Initial Setup: • Initializing Display Modes, e.g. Color mode, Single/Double Buffer, etc. • Entering GLUT event processing loop • void glutMainLoop (void)

12. Display Function • The display function of current window • When is it called? • If the normal plane of a window needs to be redisplayed as a result of window damage. GLUT determines this based on redisplay state of a window. • When a user requests. • How is it called? • Implicitly: By GLUT, e.g. when the window system reports a region of the window's normal plane is undefined (for example, damaged by another window moving or being initially shown) • Explicitly: Using glutPostRedisplay function.

13. Double Buffering • Using Two buffers • Front Buffer • Back Buffer • Is specified in initialization step • glutInitDisplayMode (GLUT_DOUBLE) • Replace glFlush() with glSwapBuffers() • Increases the performance • It’s NOT free, you have to pay: memory

14. Rotation and Translation

15. Camera Rotation • Example: If we want to move a camera along a circular path and about any one of axes, we use rotation matrix corresponding to that axis. • Then, by increasing the angle from [0…360], we calculate the new location of the camera.

16. ModelView,Projection,Viewport • ModelView: • Rotation, Translation, Scale. • Projection: • glFrustum, glOrtho, glPerspective • Viewport • glViewport

17. Perspective Projection

18. Viewport • Defines how a rendered image should be displayed on a window.

19. Sequence of Matrices

20. Camera • Properties: Position, Direction, UpVector • Attention: • Using gluLookAt affects the ModelView Matrix • It is usually placed at the beginning of the display function • It is usually placed after glLoadIdentity(GL_MODELVIEW) • Be careful when placing it in a loop.

21. Matrix Stack • Pushing matrices into the stack • Poping matrices from the stack • Example: