3D Viewing Pipeline

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3D Viewing Pipeline
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Learning Objectives

• 3D viewing pipeline
• OpenGL functions for 3D viewing

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Learning Objectives

• Understand the 3D viewing pipeline.
• Understand OpenGL 3D viewing functions.

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3D Viewing Pipeline

• Procedures for displaying views of a
  three-dimensional scene on an output device
  involve many aspects
• Generate a 3D scene with objects generally
  defined with a set of surfaces forming a closed
  boundary around the object interior.
• Generate interior of 3D objects, if needed.
• Project object surfaces views onto the surface of
  a display device with 3D viewing pipeline.
• Identification of visible parts.
• Lighting effects and surface characteristics.

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3D Viewing Pipeline
(from Donald Hearn and Pauline Baker)
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3D Viewing Pipeline

• 3D viewing pipeline similar to taking a picture
  with a camera
• Construct and model the scene in world
  coordinates.
• Choose a viewing position corresponding to where
  we would place a camera, depending whether we
  want a front, back, top, bottom, or side of the
  scene, or inside of an object, or within group.
• Choose camera orientation.

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3D Viewing Pipeline

• 3D viewing pipeline similar to taking a picture
  with a camera
• Convert the description of the scene to viewing
  coordinates, which includes the position and
  orientation of the projection plane, called the
  view plane, similar to a camera film plane.
• Convert and project the viewing coordinates into
  projection coordinates of the 2D clipping region
  selected called the view volume and defined as
  a volume of space enclosed in clipping planes.
• Transform viewing-coordinates to
  normalized-coordinates (ex between 0 and 1, or
  between -1 and 1), clipping off parts of the
  scene outside the view volume.
• Map normalized-coordinates to device-coordinates.

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3D Viewing Pipeline
(from Donald Hearn and Pauline Baker)
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3D Viewing Pipeline

• 3D viewing pipeline projection transformations
• Parallel projection parallel lines are
  transformed into parallel lines can be
  orthogonal or oblique.
• Orthogonal projection projection lines are
  perpendicular to the view plane.
• Oblique parallel projections projection lines
  are all parallel and not perpendicular to the
  view plane.
• Cavalier projection angle 45 degrees
• Cabinet projection angle 63.4 degrees / tan
  (angle) 2
• Perspective projection does not conserve parallel
  lines nor objects proportions.
• Frustum is the view volume between near and far
  clipping planes, and has the shape of a truncated
  pyramid.

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3D Viewing Pipeline
(from Donald Hearn and Pauline Baker)
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3D Viewing Pipeline
(from Donald Hearn and Pauline Baker)
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3D Viewing Pipeline

• OpenGL 3D viewing functions
• Modeling of 3D scene
• Geometric transformation of viewingglMatrixMode
  (GL.GL_MODELVIEW)
• Viewing parameters specificationglLookAt (x0,
  y0, z0, xref, yref, zref, Vx, Vy, Vz) where
  P0(x0, y0, z0) is viewing position in
  world-coordinates (camera position)where
  Pref(xref, yref, zref) is reference position
  (look-at point) where V(Vx, Vy, Vz) is the
  view-up vector (opposite to viewing
  direction)default P0(0, 0, 0) and Pref(0, 0,
  -1) and V(0, 1, 0) (negative zworld axis)
• Projection mode
• glMatrixMode (GL.GL_PROJECTION)
• glLoadIdentity()
• Clipping window
• Orthogonal projection near clipping plane is
  the view planegluOrtho(xwmin, xwmax, ywmin,
  ywmax, dnear, dfar)defaults are (-1.0, 1.0,
  -1.0, 1.0, -1.0, 1.0) (cube centered on
  coordinate origin)

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3D Viewing Pipeline

• OpenGL 3D viewing functions
• Clipping window
• Perspective projection with symmetric frustum
  volume gluPerspective (theta, aspect, dnear,
  dfar)where theta is the field-of-view angle
  (angle between top and bottom clipping
  planes)where aspect is the value for the aspect
  ratio (width / height) of the clipping
  windowdnear and dfar are the positions of the
  near and far clipping planes and need to be on
  the negative zview axis (in front of the viewing
  position), although their positive values are
  transformed into dnear and -dfar
• Perspective projection with symmetric or not
  frustum volume glFrustum (xwmin, xwmax, ywmin,
  ywmax, dnear, dfar)where near plane is the view
  planewhere xwmin, xwmax, ywmin, ywmax are the
  coordinates of the clipping window on the near
  planednear and dfar are the positions of the
  near and far clipping planes and need to be on
  the negative zview axis (in front of the viewing
  position), although their positive values are
  transformed into dnear and dfar.

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3D Viewing Pipeline

• OpenGL 3D viewing functions
• Viewport
• glViewport (xvmin, yvmin, vpwidth,
  vpHeight)default is size of the display
  windowwhere xvmin and yvmin represent the
  integer position of the lower-left corner of the
  viewportwhere vpwidth and vpheight give the
  integer width and height of the viewport.
• glGetIntegerv (GL.GL_VIEWPORT, vpArray)returns
  an array of integers containing the current
  viewport parameters xvmin, yvmin, vpwidth,
  vpHeight.

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3D Viewing Pipeline
(from Donald Hearn and Pauline Baker)
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3D Viewing Pipeline

• Example Chap73DViewingPipeline.javaperspective
  projection of a square