Digital Media
Dr. Jim Rowan
ITEC 2110
Thursday, September 13
Roll call
Barton, Paul H.
Bois, Lauren C.
Bonds, Allison E.
Duncan, Jarred T.
Lawson, Joseph I.
Mulongo, Julio B.
Pennison, Heather L.
Reilly, Daniel J.
Sanchez-Casas, Jon F.
Simson, Davis
Sinnock, Grant A.
Swaim, Mark S.
Tran, Dung Q.
Vyas, Anand A.
Woldeyohannes,
Tesfamichael
Roll call
Jones, Crystal L.
Marsh, Kerreen A.
Thompson, Daniel G.
Tran, Christopher V.
vector graphics:
shapes
• 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
points
• 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
http://en.wikipedia.org/wiki/Ellipse
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
together
• 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 filled
– 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
Manipulating
objects AKA closed curves
• Translation is a simple up/down side-toside 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
3-D
• Way more complex than 2-D
• 3-D shapes (objects) are defined by their
surfaces
• 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!
Car
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 nonrational 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
complexity
• 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
heuristics
• 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
Questions?