Program 2 due 02/01

1
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

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Indexed Color

• Needed for frame buffers with a limited depth
• 8 bits of color 28 colors 256 colors
• default is dividing bits into rbg assignments
• load color map with a pallette of 256 colors
• LUT

3
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.

4
Matrix Modes

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

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Clients and Servers

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

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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

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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

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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).

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Interaction

• According to Websters
• To act upon each other
• Two way communication
• GLUT toolkit for windowing
• GLUT recognizes only a small subset of the events
  recognized by X

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Input

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

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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 request program.
• Process trigger process measure.

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Input Modes

• Sample mode
• Measure returned when triggered
• Measure sample program
• Process measure
• Event mode
• Device triggered
• Event generated
• Device measure placed on the event queue
• Event type tied to function called CALLBACK

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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.

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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

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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

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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

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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)

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Display Callback

• Invoked when GLUT determines the window should be
  redisplayed
• Upon opening it initially

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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.

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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

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Adding a Menu

• glutCreateMenu
• (menu_callback_name)
• glutAddMenuEntry("quit",1)
• glutAttachMenu
• (GLUT_RIGHT_BUTTON)

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Adding a menu callback

• menu_callback_name(int id)
• if (id .
• .
• .

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Animation

• Double buffering eliminates flicker.

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Callback Advice From the Creator of GLUT, Mark
Kilgard

• Dont 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.

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More Callback Advice

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

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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

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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

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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.

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Homework

• Read chapter 4
• Program 2 due 02/01/05