Vannevar Bush - MEMEX
Ivan Sutherland - Sketchpad
MIT - Spacewar
Douglas Engelbart - NLS (oNLine System)
Xerox PARC - Star
Change in response to users' actions
Lets users know that they're interacting
Immediate, simple response often useful
Can be visual, auditory, haptic
Delay between an action and its result
Humans very aware of latency > ~ 100 milliseconds
Many delays inherent in different stages of hardware/software
"End-to-end" latency = total delay
Long latency slows up user
Irregular latency even worse
Latency is distinct from update speed
Measure of how many distinct values a device can report
On/off switch = 1 bit resolution
"Non-analog" joystick = 3 values (+1, 0, -1) for X and for Y
8 bit resolution joystick = 256 possible values for X and for Y
16 bit resolution joystick = 65536 possible values for X and for Y
Signal = the information we want to communicate to the computer (e.g. button state, pointer position)
Noise = variations in the signal, outside of our control
Examples:
Applications may need to allow for noise in input data
From human movement research - Paul Fitts, 1954
Predicts time needed to move from a starting position to a target - e.g. to point at something
D = distance to target
W = width of target
| glutKeyboardFunc(func) | Called when a 'character' key is hit |
| glutSpecialFunc(func) | Called when a 'special' key is hit |
| glutKeyboardUpFunc(func) | Called when a 'character' key is released |
| glutSpecialUpFunc(func) | Called when a 'special' key is released |
| glutGetModifiers() | Returns state of shift, control, alt keys when event happened |
| glutIgnoreKeyRepeat(val) | Tells GLUT whether to ignore automatic keyboard repeat |
All keyboard callback functions take the form:
def func(key, x, y):
...
key is the key pressed or released - either a single-character string (e.g. 'a'), or a special-key constant (e.g. GLUT_KEY_UP)
x, y is the mouse pointer location when the key event occurred
Note: in Python, the same function can be used for both normal & special keys
glutGetModifiers() returns a bit-mask value
i.e. a combination of flags
Possible flags are GLUT_ACTIVE_SHIFT, GLUT_ACTIVE_CTRL, and GLUT_ACTIVE_ALT
Test a flag with the & operator. e.g.:
if glutGetModifiers() & GLUT_ACTIVE_CTRL:
doSomethingForCtrlKey()
| glutMouseFunc(func) | Called when a mouse button is pressed |
| glutMotionFunc(func) | Called when mouse moves, while button pressed |
| glutPassiveMotionFunc(func) | Called when mouse moves, with no button pressed |
| glutGetModifiers() | Returns state of shift, control, alt keys when event happened |
Mouse-button callback functions take the form:
def func(button, state, x, y):
...
button is the button pressed or released - one of GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, or GLUT_RIGHT_BUTTON
state is GLUT_DOWN if the button was pressed, or GLUT_UP if it was released
x, y is the mouse pointer location when the button was pressed or released
Mouse-motion callback functions take the form:
def func(x, y):
...
x, y is the new mouse pointer location
| glutJoystickFunc(func, t) | Called every t milliseconds with current joystick state |
| glutTabletMotionFunc(func) | Called when the tablet puck is moved |
| glutTabletButtonFunc(func) | Called when a tablet button is pressed or released |
| glutDialsFunc(func) | Called when a dial is turned (dial/button box) |
| glutButtonBoxFunc(func) | Called when a dial/button box button is pressed or released |
Typical computer GUIs (graphical user interfaces) use "widgets"
Higher-level interface, built on top of basic devices plus graphics display
Examples:
Most reproduce the functionality of physical devices
GLUT provides simple pop-up menus
A menu is attached to a mouse button, and appears whenever that button is pressed
If a menu entry is selected, a callback is called with a value associated with that entry
Menus can include sub-menus
| id = glutCreateMenu(func) | Starts defining a new menu (or submenu) |
| glutAddMenuEntry(label, value) | Adds a selectable entry to the current menu |
| glutAddSubMenu(label, id) | Adds a submenu to the current menu |
| glutAttachMenu(button) | Defines mouse button to pop-up the current menu |
Examples:
menu0.py
menu1.py
menu2.py
Each menu has a unique ID - a number
ID primarily needed when creating submenus
Value associated with a menu entry must be a single integer
Menus can be changed dynamically
(See glutSetMenu, glutRemoveMenuItem, glutChangeToMenuEntry, glutChangeToSubMenu)
Menus can also be attached & detached from buttons dynamically (See glutDetachMenu)
