1 Review of COMPSCI 221  Chapters 1-11 in text  User Interfaces will be addressed as a take- home question

2 Computer Graphics Modeling: Creating a virtual world. Rendering: Generating a visual image of a scene.

3 Java2D  Graphics2D class manages the rendering  Use a Panel to provide the Graphics context  Use JApplet or JFrame as root container

4 Graphics2D Class  Properties –Foreground color –Font –Stroke –Paint  Capabilities –drawing and filling Shape objects –applying AffineTransforms

5 2D Objects  A 2D object consists of a set of points in a plane  Examples –point –lines, curves –shapes like rectangles, ellipses, arcs, polygons –text and images

6 Parametric Equation  Parametric equation expresses each coordinate in terms of a parameter x = f(t)‏ y = g(t)‏  The parametric equation for an ellipse is x = x 0 + a cos t y = y 0 + b sin t

7 Custom Shapes  Area combines shapes to create more complex objects  Set-theoretic operations –Intersect –Add –Subtract –Exclusive or  PathIterator interface allows Shape object to return an iterator to sub- parts  Path2D constructs an outline from a sequence of lines and curves –moveTo –lineTo –quadTo –curveTo –closePath

8 Coloring Objects  Paint interface supports –Color - create a color by giving the amount od red, green, blue to make the color –Gradients - interpolations between two different colors –Texture - use an image to "color" an object

9 Strokes  The Stroke interface defines a method for creating an outline from a shape  BasicStroke class has the following properties –Width –End style (butt, round, square)‏ –Join style (bevel, miter, round)‏ –Miter limit (limits miters on small angle joins)‏ –Dash pattern and phase

10 Affine Transformation  Maps parallel lines to parallel lines  Common affine transforms in both 2D and 3D –Translation –Rotation –Reflection –Scale –Shear

11 Clipping Path A rendered image may be clipped by a clipping path

12 Text in Java2D  Text is treated as a special kind of geometric object  A Font defines the rendering shapes of all the characters  Geometry of a text string in a particular font is represented by a GlyphVector  Create a Shape from the GlyphVector

13 BufferedImage  A BufferedImage contains –Raster -- holds the pixel values –ColorModel -- specifies how to interpret pixel values  BufferedImage has a create Graphics method which allows you to draw to the image  BufferedImageOps –RescaleOp - scale pixel values linearly –LookupOp - use a table to convert pixel values –ConvolveOp - convolute pixel value with thos of neighbors –ColorConvertOp - pixel-by- pixel color conversion –AffineTransformOp - apply the specified transformation to each pixel

14 Animation  You need a way to make something happen at regular intervals –Change some parameter used by the paintComponent method –call repaint() or revalidate() to cause paintComponent to be called  Timer is a Swing Component –delay can be set –generates an ActionEvent after each delay period –register a Listener to respond to the event

15 3D Model and View

16 Java 3D  High-level API  Scene is represented as a scene graph object –Content branch defines the onjects in the scene –View branch defines how the scene is viewed  VirtualUniverse –SimpleUniverse  Locale  Nodes –Group nodes –Leaf nodes  NodeComponents –attached to one or more nodes

17 Background and Bounds  Default background is black  Create custom background with the Background node –set the color –use an image –use a geometry  Environmental nodes need to be limited in extent –e.g. lights, background –limits amount of rendering to be done  Two ways: –Bounds, node component –BoundingLeaf, a Node  uses a Bounds object

18 Points and Vectors  Point represents position  Vector represents direction  Both can be represented as a tuple  An n-dimensional vector is an n-tuple of numbers –(x 1, x 2, …, x n )‏

19 Shapes in 3D  Use a Shape3D Node to represent visual objects –A Shape3D leaf node usually references Geometry and Appearance node components  Geometry is abstract class with many subclasses –GeometryArray –IndexedGeometryArra y –Text3D

20 GeometryArray  Supports construction of objects using arrays of points, lines and polygons  Defines an array of vertices along with other properties that are associated with them –normals –color (3 or 4 elements)‏ –texture coordinates (2, 3 or 4 elements)‏

21 Transform3D  A higher-level representation for transformations  Has constructors to create from both Matrix objects and from vectors  Also has set and get methods for the internal 4 x 4 matrix  Can also set a particular type of transformation

22 Views  View Volume –represented by a projection matrix  View positioning –represented by a view matrix  View Properties –Projection type –Field of view –Limits to view distance –Size of view plate

23 Projections  A projection maps a point in the virtual world onto a view plane –view plate is a finite window in the view plane –also limit the depth that is rendered  Two types of projection –parallel –perspective

24 Types of Lights  Ambient light –uniform in all directions and locations  Directional light –models a distant light source whose rays are all parallel  Point light –light located at a particular location which emits in all directions –Intensity decreases with distance  Spot light –Like a point source except the direction of the emission is restricted

25 Geometry of Reflection  For perfectly reflective surface –angle of incidence = angle of reflection –no loss of intensity  In reality surfaces aren't perfect –light gets scattered –light can be absorbed  Phong model I = I a k a + I p k d cos  + I p k s cos n  –k a, k d, k s are coefficients for ambient, diffuse and specular reflection for a particular material –n is the shininess coefficient, also a property of the material

26 Appearance  Node component which has components that control various aspects of the appearance of an object. –ColoringAttributes, RenderingAttributes, TransparencyAttributes –PointAttributes, LineAttributes, PolygonAttributes –Material –TextureAttributes, Texture, TexCoordGeneration, TextureUnitState

27 Material  Contains components to control the color contributed by different kinds of lighting –ambient, diffuse, specular –can also contain an emissive color component  Shininess coefficient affects specular reflection  Color target for per-vertex colors

28 Depth Cueing  Atmospheric attenuation effects can be simulated with depth cueing  Blend the objects with background color (or with arbitrary fog color)‏ C = f C 0 + (1 - f) C f  Blending is an increasing function of the distance –linear –exponential –gaussian

29 Texture Mapping  Real surfaces often have a large amount of detail  Use a digital image to provide complex detail with minimal computational cost  Procedural textures use a function to calculate the color at any given point

30 Behavior  Java3D uses behavior to facilitate dynamics in a scene graph  Behavior is a leaf node –Defines actions to be taken when the behavior is activated (waked-up)‏ –Behavior is triggered by wakeup conditions  For interactions, triggers are user generated  For animation, triggers are time-based

31 Interpolators for Animation  Interpolator is an abstract subclass of Behavior –It has a number of predefined subclasses containing typical behaviors needed for animation  For example, Color, Switch, Transparency, Transform  The idea is to set two values for a particular attribute and interpolate values in between as a function of time  Alpha object is used to trigger the changes

32 Alpha  A function of time –usually periodic  Has a range from 0.0 to 1.0

33 User Interfaces  Design principles –User should be in control –Reduce memory load for users –Be consistent  Useability heuristics –Ease of learning and remembering –Efficiency of use –Minimize errors  Facilitate recovery from errors