Version 1 - Just a Bunch of Lines

• Bare minimum - defaults wherever possible
• Harcoded vertices
• GL_LINE_LOOP
• Things to watch out for:
  • The order in which the vertices are specified
  • GL_LINES, GL_LINE_STRIP

Version 2 - Change the View

• Add an init function
• Changing the view is a model-view transformation, so we have to specify we want to modify the model view matrix
  • glMatrixMode(GL_MODELVIEW)
  • glLoadIdentity() initializes the model view matrix for us
  • gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz)
• Things to watch out for:
  • Remember the default is orthographic viewing, with a 2x2x2 cube with the eye at the center
    • You thus see things behind you
  • Move the eye away from the origin and things might no longer be within your clipping volume
  • Forgetting to set the matrix mode to GL_MODELVIEW
  • Forgetting to call glLoadIdentity -- GIGO

Version 3 - Add Some Color

• glClearColor(r, g, b, a) - sets 'clear' color (i.e., background) for the color buffer
• glClear(buffer bitmask) - sets one or more buffers to the value for each buffer
• glColornt[v] - sets current color
• Things to watch out for:
  • Make sure you color is different than your clear color (duh)

Version 4 - Specify Vertices Using Vectors (Arrays)

• Use typedef to define a POINT3 type
  • Use the GLfloat data type
• Respecify the each vertex as an array of 3 (x, y, z) coordinates

Version 5 - Turn it into an Array of Vertices

• Basically have a 2-dimensional array
  • Each vertex is an array of 3 coordinates
  • Have an array of vertices

Version 6 - Specify Window Size and Position

• glutInitWindowSize(width, height)
• glutInitWindowPosition(x, y)
• Things to watch out for:
  • The aspect ratios of the window size and clipping volume should match, or you'll get distortion of the image

  Version 7 - Change Clipping Volume

  • Clipping volume in orthographic projection is a cube
  • glOrtho(left, right, top, bottom, near, far);
    • relative to the eye (at 0, 0, 0)
    • negative values for near/far are behind the eye
  • Affects the projection matrix
  • Things to watch out for:
    • Forgetting to set the matrix mode to GL_PROJECTION
    • Forgetting to initiali the matrix using glLoadIdentity
    • Miscalculating distance to object(s) being viewed

  Version 8 - Polygons

  • Change the GL_LINE_LOOP to GL_POLYGON
    • Polygons have faces which by default are filled with the current color
      • Face filling can be controlled with glPolygonMode(face, fillMode)
  • Things to watch out for:
    • If it's not specified as a polygon, it's has no face and is not filled.

  Version 9 - Specifying all the Polygons

  • Change the GL_LINE_LOOP to GL_POLYGON
    • Polygons have faces which by default are filled with the current color
      • Face filling can be controlled with glPolygonMode(face, fillMode)
    • We'll specify a different color for each face
  • Things to watch out for:
    • If it's not specified as a polygon, it's has no face and is not filled.

  Version 10 - Hidden Surface Removal

  • Normally lines are drawn/rendered/rasterized in the order specified
    • By default no depth information is used.
  • Introducing depth testing provides hidden surface removal
    • Objects closer to the eye hide objects behind them
  • To use depth testing, you must:
    • Specify that a depth buffer is to be used
      • glutInitDisplayMode(GLUT_DEPTH)
      • Usually placed in main
    • Enable depth testing (using the buffer)
      • glEnable(GL_DEPTH_TEST)
      • Usually placed in init
    • Clear the depth buffer prior to display
      • glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
  • Things to watch out for:
    • Forgetting to vlear the depth buffer bit-- buffer will contain data (probably garbage) from last display

  Version 11 - Parameterizing the Image

  • Makes handling resizing the image easier
  • Can also simplify specifying the image in the first place

  Version 12 - Handling Window Resizing by Adjusting Clipping Volume

  • The clipping volume is mapped onto the viewport which is mapped onto the window
    • This can introduce distortion of the aspect ratios don't match
    • This can occur if user resizes the window
    • This can also cause clipping since the viewport hasn't changed
  • Must maintain match between aspect ratios
  • One way to accomplish this is to adjust the clipping volume when window is resized

  Version 12 - Handling Window Resizing by the Viewport

  • The clipping volume is mapped onto the window
    • This can introduce distortion of the aspect ratios don't match
    • This can occur if user resizes the window
  • Must maintain match between aspect ratios
  • One way to accomplish this is to adjust the clipping volume when window is resized

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