Chapter 3 Viewing

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Chapter 3 Viewing
2
Contents

• Overview The Camera Analogy
• Viewing and Modeling Transformation
• Projection Transformation
• Viewport Transformation

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Chapter Objectives

• View a geometric model in any orientation
• Control the location in 3D space
• Clip Undesired portions of the model

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Overview -The Camera Analogy-
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Overview The Camera Analogy

• Viewing Transformation
• Positioning the view volume in the world
• Modeling Transformation
• Positioning models in the world
• Projection Transformation
• Determining the shape of the view volume
• Viewport Transformation

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Method for Transformation - 1

• The Viewing Transformation
• glTranslatef()
• glRotatef()
• gluLookAt()
• The Modeling Transformation
• glTranslatef()
• glRotatef()
• glScalef()

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Method for Transformation - 2

• The Projection Transformation
• Perspective
• Orthographic
• Order of Setting
• glMatrixMode(types)
• glLoadIdentity()
• glFrustum() or gluPerspective(), glOrtho()

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General-Purpose Transformation Commands

• glMatrixMode(GLenum mode)
• Specifies which matrix will be modified
• GL_MODELVIEW, GL_PROJECTION, GL_TEXTURE
• glLoadIdentity()
• Sets the currently modifiable matrix to the 44
  identity matrix

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General-Purpose Transformation Commands

• glMultMatrixfd(const Type m)
• Multiply the current matrix by the matrix passed
  in as an argument
• glLoadMatrixfd(const Type m)
• Set the 16 values of the current matrix to those
  specified by m

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Viewing and Modeling Transformations
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Thinking about Transformation

• To performing viewing or modeling transformation
• glMatrixMode(GL_MODELVIEW)

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2 Types of Coordinate System

• Example
• glMatrixMode(GL_MODELVIEW)
• glloadIdentity()
• glMultiMatrixf(N)
• glMultiMatrixf(M)
• glBegin(GL_POINTS)
• glVertex3f(v)
• glEnd()
• Grand, Fixed Coordinate System
• Moving a Local Coordinate System

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Modeling Transformation

• Translate
• Void glTranslatefd(x, y, z)
• Rotate
• Void glRotatefd(angle, x, y, z)
• Scale
• Void glScalefd(x, y, z)
• glScalef(2.0, -1.5, 1.0)

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Viewing Transformation - 1

• glTranslate() or glRotate()
• Moving forward camera
• Moving Backward Object
• gluLookAt()
• Void gluLookAt(
• eyex, eyey, eyez,
• centerx, centery, centerz,
• upx, upy, upz)

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Viewing Transformation - 2

• Creating a Custom Utility Routine
• Void PilotView(GLdouble planex, Gldouble planey,
  Gldouble planez, Gldouble roll, Gldouble pitch,
  Gldouble heading)
• glRotated(roll, 0.0, 0.0, 1.0)
• glRotated(pitch, 0.0, 1.0, 0.0)
• glRotated(heading, 1.0, 0.0, 0.0)
• glTranslated(-planex, -planey, -planez)

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Projection Transformations
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Projection Transformations

• Purpose
• To define a viewing volume
• How an object is projected onto the screen
• How to Clip the object
• Setting for projection transformation
• glMatrixMode(GL_PROJECTION)
• glLoadIdentity()

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Perspective Projection - 1

• Foreshortening
• The farther, the smaller object appears in the
  final image
• glFrustum(left, right,
• bottm, top, near, far)

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Perspective Projection - 2

• gluPerspective(fov, aspect, near, far)

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Orthographic Projection -1

• View Volume
• Rectangular parallelepiped

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Orthographic Projection -2

• glOrtho(left, right, bottom, top, near, far)
• glOrtho2D (left, right, bottom, top)

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Viewport Transformation
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Defining the Viewport

• glViewport(x, y, width, height)
• gluPerspective(fov, 2.0, near, far)
• glViewport(0, 0, 400, 200)
• The Transformed
• Depth coordinates

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Program Demo

• Transformation\lesson1.exe