logical input devices (CG) part-2

Note: in this note I'm discussed one of important question of CG

LOGICAL INPUT DEVICES:

 These are characterized by its high-level interface with the application program rather than by its physical characteristics.
 Consider the following fragment of C code:

int x;
scanf(“%d”,&x);
printf(“%d”,x);

 The above code reads and then writes an integer.
Although we run this program on workstation providing input from keyboard and seeing output on the display screen.
the use of scanf() and printf() requires no knowledge of the properties of physical devices such as keyboard codes or resolution of the display.
These are logical functions that are defined by how they handle input or
output character strings from the perspective of C program.
 From logical devices perspective inputs are from inside the application
program.
The two major characteristics describe the logical behavior of input devices are as follows:

API defines six classes of logical input devices which are given below:

String :
A string device is a logical device that provides the ASCII values of input characters to the user program. This logical device is usually implemented by means of physical keyboard.

A locator device provides a position in world coordinates to the user program. It is usually implemented by means of pointing devices such as mouse or track ball.

3. PICK:
A pick device returns the identifier of an object on the display to the user program. It is usually implemented with the same physical device as the locator but has a separate software interface to the user program.
In OpenGL, we can use a process of selection to accomplish picking.
4. CHOICE:
A choice device allows the user to select one of a discretenumber of options. In OpenGL, we can use various widgets provided by the window system.
A widget is a graphical interactive component provided by the window system or a toolkit. The Widgets include menus, scrollbars andgraphical buttons.

For example, a menu with n selections acts as a choice device, allowing user to select one of ‘n’ alternatives.

5. VALUATORS:
They provide analog input to the user program on somegraphical systems; there are boxes or dials to provide value.

6. STROKE:
A stroke device returns array of locations. Example, pushingdown a mouse button starts the transfer of data into specified array and releasing of button ends this transfer.