Program 2 due 02/01  Be sure to document your program  program level doc  your name  what the program does  each function  describe the arguments  describe what the function does  document anything you may forget in a week

Indexed Color  Needed for frame buffers with a limited depth  8 bits of color = 2**8 colors = 256 colors  default is dividing bits into rbg assignments  load color map with a pallette of 256 colors  LUT

Viewing  Camera and objects are specified independently.  For a 2D world - define viewing or clipping rectangle.  Objects inside will be seen.  Objects outside will not be seen.  For a 3D world - define a viewing volume.  Orthographic projection.

Matrix Modes  Pipeline graphics dependent on concatenating a number of transformation matrices. Vertices Transformer Clipper Projector Rasterizer Pixels  Matrices  model-view  projection

Clients and Servers  Graphics server  Workstation with raster display, keyboard, and pointing device  Provides input and output services for network  Client  OpenGL application programs

Display Lists  From display processor  A special purpose computer  Host computer sent instructions to the display processor  Instructions stored in display memory as a display file or a display list  Immediate mode  Program defines a primitive  Primitive sent to server for display  No memory of primitive exists

Display Lists  Retained mode graphics  Define object once  Put description in a display list  Display list stored on the server  Redisplayed by a single function call  Advantage  Reduced network traffic  Disadvantage  Memory required on the server  Creating the display list has overhead

Display Lists  Creation of a display list - use glNewList, glEndList to encapsulate the list.  Each list has an int identifier which can be invoked with the command glCallList(identifier);  Save attributes with the matrix and attribute stacks (remember from 202: push onto a stack and pop off of a stack).

Interaction  According to Webster’s  To act upon each other  Two way communication  GLUT toolkit for windowing  GLUT recognizes only a small subset of the events recognized by X

Input  Input devices  Logical devices  From the perspective of the application program  Physical devices  Hardware and how it works

Input Modes  Mode defined by the relationship between the trigger and the measuring process.  Trigger (physical input that user signals computer).  Measure (what is returned to the program).  Request mode.  Measure returned when triggered. Trigger measure requestprogram. Process triggerprocess measure.

Input Modes  Sample mode  Measure returned when triggered Measure sampleprogram Process measure  Event mode  Device triggered  Event generated  Device measure placed on the event queue  Event type tied to function called CALLBACK

Input Modes Trigger measure event await program. Process trigger process measure queue event.  Event mode.  Device triggered.  Event generated.  Device measure placed on the event queue.  CALLBACK registered with the windowing system. Event type tied to function called a callback.

Using the Pointing Device Mouse Triggered Events  Move event  Move the mouse with the buttons depressed  Passive move event  Move the mouse without pressing a button  Mouse event  When one of the buttons is either released or pressed

Specify the Mouse Callback Function  In main()  With glutMouseFunc(mouse_callback_func)  void mouse_callback_func(int button, int state, int x, int, y)  The callback function specifies what actions are related to the specified event

Window Event  Generated when the window is resized  Redraw all the objects in the window  How to handle the aspect ratio  Do we change the sizes or attributes of the new primitives if the size of the new window is different from that of the old

Keyboard Events  Generated when the mouse is in the window and one of the keys is depressed  Returns the ascii code for the key and the x and y coordinates of the mouse  void keyboard(unsigned char key, int x, imt y)

Display Callback  Invoked when GLUT determines the window should be redisplayed  Upon opening it initially

Idle Function  Idle callback invoked when there are no other events.  Generates graphical primitives through a display function while nothing else is happening.  Event processing happens between calls to the idle function.  Do not spend too much time in the idle function.  Idle does not actually rerender the frame.  To rerender call glutPostRedisplay(); from within the idle callback.

Menus  GLUT provides popup menus  glutCreateMenu(menu_callback_name);  Menu_callback_name is the name of the function. The argument to that function is the identifier passed to the callback when the entry is selected

Adding a Menu glutCreateMenu(menu_callback_name);glutAddMenuEntry("quit",1);glutAttachMenu(GLUT_RIGHT_BUTTON);

Adding a menu callback menu_callback_name(int id) { if (id ==. if (id ==...}

Animation  Double buffering eliminates flicker.

Callback Advice From the Creator of GLUT, Mark Kilgard  Don’t change state that will affect the way a window will be drawn a display callback.  If you need to redisplay a window, instead of rendering in whatever callback you happen to be in, call glutPostRedisplay.  If you use an idle callback to control animation, use a visibility callback to determine when the window is fully obscured or iconified.

More Callback Advice  The backspace, Esc, and Del keys generate ASCII characters, so detect key presses for these keys using the glutKeyboardFunc callback.

Design of Interactive Programs  A smooth display (no flicker or artifacts of the refresh process)  A variety of interactive devices on the display  A variety of methods for entering and displaying information  An easy to use interface that does not require substantial effort to learn  Feedback to the user  Tolerance for user errors  A design incorporation for consideration of both the visual and motor properties of the human

Limitations of Geometric Rendering  Designing widgets  example of popup menu  refreshing the display where the menu was  no primitives but uses scan line image data  operations described in terms of the frame buffer or in terms of bit-block transfer operation

Limitations of Geometric Rendering  Rubberbanding  a technique for displaying line segments in a changing manner.  Endpoint is selected  Before second endpoint is selected a line segment is drawn automatically to where the present position of the mouse is  As the mouse moves the old segment must be erased and a new one drawn.

Homework  Read chapter 4  Program 2 due 02/01/05