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Digital Media


									   Digital Media

    Dr. Jim Rowan
      ITEC 2110
Thursday, September 13
                   Roll call
Barton, Paul H.
                       Sanchez-Casas, Jon F.
Bois, Lauren C.
Bonds, Allison E.      Simson, Davis
Duncan, Jarred T.      Sinnock, Grant A.
Lawson, Joseph I.      Swaim, Mark S.
Mulongo, Julio B.      Tran, Dung Q.
Pennison, Heather L.   Vyas, Anand A.
Reilly, Daniel J.
             Roll call
Jones, Crystal L.
Marsh, Kerreen A.
Thompson, Daniel G.
Tran, Christopher V.
            vector graphics:
• shapes are inherently defined internally
• makes it easy to move the shapes around
• straight lines are created with a line tool
  – internally the line is stored as its endpoints
• connected lines are stored as a polyline
  – internally the polyline is stored as a series of
• closed polylines form a shape
         vector graphics:
     rectangles and squares
• rectangles can be described by two corners
• squares are special cases of the rectangle
              vector graphics:
             ellipses and circles
  • ellipses can be described by two points
  • circles are special cases of the ellipses
     vector graphics: curves
• Question: How would you draw a curve
  using a computer with a mouse?

• You can’t draw smooth lines very easily
• Create a tool with handles based on the
  Bezier curve that can be manipulated
  by those handles
         Lines and curves
• Bezier curves can be smoothly joined
• An anchor point is the point where one
  joins the other
• When a curve closes on itself it is
  considered a closed curve
• When it doesn’t it’s an open curve
           Lines and curves
• Closed (and open for that matter) lines can be
  – This is how drawn shapes become objects like the
    cowboy on Toy Story
  – solid color, patterns or gradient (linear or radial)
  – Patterns are built of tiles that match when placed
    side to side
• Lines have ends
  – ends can be messy when joined
  – mitre, rounded, square, bevel
  objects AKA closed curves
• Translation is a simple up/down side-to-
  side movement
• Scaling: make bigger or smaller
• Rotation about a point
• Reflection about a line
                Object fills
• Solid color
• Patterns
• Gradients
  – linear
  – radial
       3-D... 3 dimensions
• x, y and z
• x & y form the ground plane
• z is the height
• Way more complex than 2-D
• 3-D shapes (objects) are defined by their
• Made even more complicated by the fact that
  a 3-D object inside the computer must be
  translated into 2-D to be rendered on a
  computer screen...
  – This results in the need to specify the viewpoint
        Structural hierarchy
• Things in the real world are
  compositions of smaller things
• Things in the 3-D graphics world are
  also compositions of smaller things
• Hierarchical structure is an excellent
  way of coping with complexity
• Also seen in object-oriented
  programming like Java and Squeak!
          Structural hierarchy
  – Wheels (4)
      • tire
      • wheel
      • hubcap
  – Doors (2)
      • handles
          – inside
              » lever
          – outside
              » button
              » handle
      • window(s)
  – Lights
      • headlights (2)
      • tail lights (2+)
      • stop lights (2+)
   3-D: additional complexity
• lighting
  – natural
  – artificial
• atmosphere
• surface texture
• rendering is extremely computationally
  expensive (demanding)
              3-D models
• Constructive solid geometry
  – uses geometric solids: cube, cylinder,
    sphere and pyramid
  – objects build by squishing and stretching
    those objects
  – objects joined using union, intersection
    and difference
         3-D models
  constructive solid geometry
• Union
  – new object is made from the space occupied by
    both objects
• Intersection
  – new object is made of the space that the two
    objects have in common
• Difference
    new object is made from
                    3-D models
                    Free Form
• Uses an object’s surface (it’s boundary with the
  world) to define it
• Build surfaces from flat polygons or curved patches
   – flat polygons are easier to render and therefore frequently
     used in games where computational power is limited
• Results in an object drawn as a “mesh”
• Can be done using Bezier surface patch but have 16
  control points
• More tractable patch uses a surface called a non-
  rational B-spline
          3-D models
      Free Form: Extrusion
• Draw a 2 dimensional shape through
  space along a line
• The line can be straight or curved
              3-D models
          Procedural modelling
• Objects are defined by formulas
• Best known is based on Fractals
• Fractals
   – exhibit the same structure at all levels of detail
   – aka “self similar”
   – used to model natural objects
• Meatballs model soft objects
• Particle systems... many particles, few controls
• Physics... distribution of mass, elasticity, optical
  properties, laws of motion
            3-D Rendering
• Rendering engine handles the
• Wire frames are used to preview
  objects and their position
  – can’t tell which surface is closer to us and
    which surface is hidden
• To save computation time, hidden
  surfaces are removed before rendering
             3-D rendering
• Lighting
  – Added to scene much like an object
  – spot light, point source, floodlight...
  – position and intensity
• Direct relationship between rendering
  quality and computational burden
                3-D rendering
• Shading... how light reacts with surface
   – Based roughly on physics but modified by
• Texture mapping
   – An image is mathematically wrapped around the object
• Light reflecting off objects of one color affect
  the color and lighting of surrounding objects
   – Two methods
      • Ray tracing Complex... must be repeated for pixel in the
        image... photo-realistic results
      • Radiosity
       3-D texture mapping
• An image is mathematically wrapped around
  the object

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