Physical input devices (computer graphics) PART-1

Physical input devices :

• Here I'm going to explain types of the physical input devices 

1.Interaction:

• In the field of computer graphics, interaction refers to the manner in which the application program communicates with input and output devices of the system.

• INPUT DEVICES :

•  Input devices are the devices which provide input to the computer 

graphics application program. Input devices can be categorized in two 
ways:

1. Physical input devices 
2. Logical input devices

•  Physical input devices are the input devices which has the particular hardware architecture. 
• The two major categories in physical input devices are:

1. 1) Key board devices:

• like standard keyboard, flexible keyboard, handheld keyboard etc.
• These are used to provide character input like letters, numbers, symbols etc.

1. 2) Pointing devices :

• like mouse, track ball, light pen etc. These are used to specify the position on the computer screen.



• 1. KEYBOARD:

• It is a general keyboard which has set of characters.
• We make use of ASCII value to represent the character i.e. it interacts with the 
  programmer by passing the ASCII value of key pressed by programmer.
• Input 
  can be given either single character of array of characters to the program.

• 2. MOUSE AND TRACKBALL:

• These are pointing devices used to specify the 
  position.
• Mouse and trackball interacts with the application program by 
  passing the position of the clicked button.
• Both these devices are similar in use 
  and construction. In these devices, the motion of the ball is converted to signal 
  sent back to the computer by pair of encoders inside the device.
• These 
  encoders measure motion in 2-orthogonal directions.
• The values passed by the pointing devices can be considered as positions
• and converted to a 2-D location in either screen or world co-ordinates.
• Thus, as a mouse moves across a surface, the integrals of the velocities yield x,y values 
  that can be converted to indicate the position for a cursor on the screen.
• These devices are relative positioning devices
• because changes in the position of the ball yield a position in the user program.

• 3. DATA TABLETS :

• :It provides absolute positioning. It has rows and
  columns of wires embedded under its surface.
• The position of the stylus is 
  determined through electromagnetic interactions between signals travelling 
  through the wires and sensors in the stylus.

• 4. LIGHT PEN:

• It consists of light-sensing device such as “photocell”.
• The light pen is held at the front of the CRT.
• When the electron beam strikes the phosphor, the light is emitted from the CRT.
• If it exceeds the threshold then light sensing device of the light pen sends a signal to the computer specifying the position.
• The major disadvantage is that it has the difficulty in obtaining a position that corresponds to a dark area of the screen 

• 5. JOYSTICK:

• The motion of the stick in two orthogonal directions isencoded, interpreted as two velocities and integrated to indentify a screen location.
• The integration implies that if the stick is left in its resting position, there is no change in cursor position.
• The faster the stick is moved from the resting position; the faster the screen location changes.
• Thus, joystick isvariable sensitivity device.

• 6. SPACE BALL:

• It is a 3-Dimensional input device which looks like a
  joystick with a ball on the end of the stick.
• Stick doesn’t move rather pressure sensors in the ball measure the forces
  applied by the user.
• The space ball can measure not only three direct forces 
  (up-down, front-back, left-right)
• but also three independent twists. So totally device measures six independent values and thus has six degree of freedom.
• Other 3-Dimensional devices such as laser scanners, measure 3-D positions directly.
• Numerous tracking systems used in virtual reality applications sense 
  the position of the user and so on.