Input Devices and Interaction

Tom Kelliher, CS 320

Feb. 26, 2003

Administrivia

Announcements

Assignment

Read 3.4--8.

From Last Time

Color, projections, viewports, project lab.

Outline

1. Input devices, programming models.

2. API.

Coming Up

Display lists, menus, picking.

Input Devices

Physical devices: Keyboard, mouse, trackball, data tablet, light pen, touch screen, joy stick.

How do mice, light pens work?

Pointing device necessary to interact with graphics.

What about 3-D interaction? (Space ball, data gloves)

Logical Input Devices

1. String.

2. Locator: Returns (x, y). Convert window coordinates to world coordinates.

3. Pick: Select an object. Must determine what object was selected.

4. Choice: widget menus.

5. Dial: scroll bars. Again, widgets.

6. Stroke: mouse drag.

Input Device Program Interaction Models

Terminology:

1. Measure: The data --- (x, y), input string, etc.

2. Trigger: User indication that the measure should be taken --- ``Enter'' key, mouse click.

Interaction modes:

1. Request (synchronous wait) mode.

   Measure not returned until trigger.

   Advantages/disadvantages.

2. Sample (asynchronous poll) mode.

   Measure returned any time.

   Advantages/disadvantages.

3. Event mode.

   Queue of (trigger, measure) pairs. Asynchronous.

   Advantages/disadvantages.

   OpenGL, callbacks, and glutMainLoop().

Input Device API

1. glutMouseFunc(pointerToMouseCallbackFunction)

2. void MouseCallbackFunction(int button, int action, int x, int y)
   1. GLUT_LEFT_BUTTON, etc.

   2. GLUT_UP, GLUT_DOWN.

   3. x and y are window-relative coordinates.

   Example:

   // ...
   
      glutMouseFunc(mouse);
   
   // ...
   
   void mouse(int btn, int action, int x, int y)
   {
      if (btn == GLUT_LEFT_BUTTON && action == GLUT_DOWN)
      {
         myInit(rows, cols, 1);
         visit(1, 1);
         glutPostRedisplay();
      }
      else if (btn == GLUT_RIGHT_BUTTON && action == GLUT_UP)
         exit(0);
   }
   

3. glutMotionFunc(pointerToMotionFunction)

   Also, glutPassiveMotionFunc().

4. void MotionFunction(int x, int y)
   1. Active motion --- mouse button depressed.

   2. How do we know which mouse button is depressed?

   3. Again, window-relative coordinates.

5. glutKeyboardFunc(pointerToKeyboardFunction)

6. void KeyboardFunction(unsigned char key, int x, int y)
   1. key is ASCII of key depressed.

   2. Yet again, window-relative coordinates.

   3. See glutSpecialFunc() for non-ASCII keys.

   Example:

   #define ESC 0x1b
   // ...
   
      glutKeyboardFunc(keyboard);
   
   // ...
   
   void keyboard(unsigned char key, int x, int y)
   {
      switch (key)
      {
         case 'w':
         case 'W':
            printf("The Clinton people took all these keys.\n");
            break;
   
         case ESC:
            exit(0);
            break;
   
         case '!':
            globalThermonuclearWar();
            // Not reached.
            break;
   
         // ...
   
         others:
            fatal("Un-recognized key.\n");
            break;
      }
   }
   

7. glutDisplayFunc(pointerToDisplayFunction)

8. void DisplayFunction(void)
   1. Callback generated by window system events.

   2. Can self-generate with glutPostRedisplay().

9. glutReshapeFunc(pointerToReshapeFunction)

10. void ReshapeFunction(GLsizei w, GLsizei h)

    As previously discussed, have to reconcile clipping region aspect ratio to window aspect ratio.