• The part of the electromagnetic spectrum with wavelengths ranging from about 380 to 740 nanometers
• A source of an electromagnetic wave creates electric and magnetic fields, perpendicular to each other, that travel away from the source
• The energy of an EM wave is stored in the electric and magnetic fields
• EM waves can travel through a vacuum

An EM Wave

• A spectral color is light of a single wavelength in the visible spectrum.
• The visible spectrum is commonly divided into seven bands named red, orange, yellow, green, blue, indigo and violet (listed in decreasing wavelength).
• It is very difficult to reproduce spectral colors using conventional techniques.

• Light from common objects (whether they are sources of light or objects that reflect light) consists of a range of different wavelengths.
• Hence, light is often characterized using a spectral power distribution that provides the power of the light at each wavelength in the visible spectrum.

The Eye

• Light enters through the cornea
• Is focused by the lens
• Stimulates sensors in the retina

• Visible Light:
  • 400 to 700 nanometers
• Rods:
  • Stimulated by short wavelengths
  • Respond quickly
• Cones:
  • \(\beta\) sensors are sensitive to wavelengths between 400 and 550 nm, but are most sensitive to a wavelength of 450 nm (what we call blue)
  • \(\gamma\) sensors are sensitive to wavelengths between 420 and 660 nm, but are most sensitive to a wavelength of 540 nm (what we call green)
  • \(\rho\) sensors are sensitive to wavelengths between 400 and 700 nm, but are most sensitive to a wavelength of 580 nm (what we call red)

• Processing the Output from Rods:
  • Impacts our perception of luminance or brightness
  • Perceived brightness is approximately logarithmic
• Processing the Output from Cones:
  • Results in our perception of color
  • The data processed by the brain is just the total levels of activity in the three types of cones

• Depth and Distance Cues:
  • Retinal disparity (between the two eyes)
  • Size
  • Shadows
• Motion Cues:
  • "On" and "Off" photoreceptors
  • Head and eye movements

• Defined:
  • A machine that is capable of presenting visual information transmitted from a computer (i.e., making information stored in a computer perceivable by the human eye)
• Types:
  • Continuous Display Space (vector devices)
  • Discrete Display Space (raster devices)

• Coordinates:
  • Quantities that designate the position of a point in relation to a given reference frame
• The Quantities:
  • Can be linear and/or angular

• Cartesian Coordinates:
  • The origin is at the center
  • The basis consists of the horizontal and vertical axes
  • Positive values in the "north east" quadrant
• An Illustration:
  • 

• Another Common Rectangular Coordinate System:
  • The origin is at the upper-left
  • The basis consists of the horizontal and vertical axes
  • Positive values in the "south east" quadrant
• An Illustration:
  • 

The (Linear) Color Cube

• The RGB Model:
  • Begin with black then add red, green, and or blue
  • An additive model
  • Often used for displays/monitors
• The CMYK Model:
  • Begin with white then remove cyan, magenta, and/or yellow
  • A subtractive model
  • Often used for printing

• Defined:
  • The process of taking an internal representation of visual content and presenting it on a visual output device
• Rendering Engines in Java:
  • Graphics
  • Graphics2D

• The "Black Box" Parts of the Process:
  • Conversion of the color space
  • Conversion of coordinate systems
  • Rasterization or vectorization of the internal representation
• Parts of the Process of Concern:
  • Clipping
  • Composition

A Translation of (25,25)

A Rotation of \(- \pi / 6\) Radians

A Scaling of (1.5, 1.5)

A Reflection About the Horizontal Axis

• Clipping Defined:
  • Limiting the portion of the object that will be "drawn" by the rendering engine
• Clipping in Java:
  • Methods in the Graphics2D class

• Composition Defined:
  • Combining the points being drawn (the source points) with the points on the background (the destination points)
• Composition Using Alpha Blending:
  • Four channels -- one each for red, green and blue and one for alpha (a weighting factor)

• The Source Over Destination Rule:
  • \(R_d = R_s + R_d (1 - \alpha_s)\)
  • \(G_d = G_s + G_d (1 - \alpha_s)\)
  • \(B_d = B_s + B_d (1 - \alpha_s)\)
  • \(\alpha_d = \alpha_s + \alpha_d (1 - \alpha_s)\)
• Alpha Blending in Java:
  • The AlphaComposite class

• The JComponent Class:
  • An part of a GUI
  • When it needs to be rendered its paint(java.awt.Graphics) method is called and is passed a rendering engine
• Rendering:
  • Write a class that extends JComponent
  • Override its paint() method

An Example

javaexamples/visual/BoringComponent.java

import java.awt.*;
import javax.swing.*;


/**
 * A concrete extension of a JComponent that illustrates
 * the process of obtaining and using a rendering engine
 *
 * @version 1.0
 * @author  Prof. David Bernstein, James Madison University
 */
public class BoringComponent extends JComponent
{

    /**
     * Render this BoringComponent
     *
     * @param g   The rendering engine to use
     */
    public void paint(Graphics g)
    {
       Graphics2D         g2;
       
       // Cast the rendering engine appropriately
       g2 = (Graphics2D)g;
       

       // Put the rendering code here
    }

}

        

• What About the Output Device?
  • We'll start by using the display/monitor
• Remember Content Panes:
  • The specialization of JComponent can be added to the content pane of a MultimediaApplication or MultimediaApplet

• Requirements:
  • Add and remove content
  • Control the \(z\)-order of content
  • Render all of the content
  • Support multiple different presentations of the same content
  • Support the transformation of visual content
  • Be thread safe
• Alternative Designs:
  • We'll consider several

A Common Design

A Design with a Problem

A Better Design

A Design that Satisfies Almost All of the Requirements

"Enhancing" the View with Specialization

A Good Design

The SimpleContent Interface

javaexamples/visual/statik/SimpleContent.java

package visual.statik;

import java.awt.*;

/**
 * The requirements of simple static visual content
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public interface SimpleContent
{
    /**
     * Render this static visual content
     *
     * @param g2   The rendering engine to use
     */
    public abstract void render(Graphics g);    
}
        

The Visualization Class

Skeleton:

javaexamples/visual/Visualization.java (Fragment: 1)

package visual;

import java.awt.event.*;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;

import visual.statik.SimpleContent;


/**
 * A collection of Content objects to be rendered
 * (and a collection of GUI components that will
 * render them)
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Visualization
{
    private   CopyOnWriteArrayList<SimpleContent> content;
    private   LinkedList<VisualizationView>       views;
    

    /**
     * Default Constructor
     */
    public Visualization()
    {
       content = new CopyOnWriteArrayList<SimpleContent>();
    
       views   = new LinkedList<VisualizationView>();

       views.addFirst(createDefaultView());       
    }

}
        

Content Management:

javaexamples/visual/Visualization.java (Fragment: content)

    /**
     * Add a SimpleContent to the "front" of this Visualization
     *
     * Note: This method only adds the SimpleContent if it is not
     * already in the Visualization.  However, the "underlying"
     * content (e.g., BufferedImage, Shape) in two different
     * SimpleContent objects can be the same.
     *
     * To change the order of a SimpleContent that is already on the canvas
     * use toBack() or toFront().
     * 
     * @param r   The SimpleContent to add
     */
    public void add(SimpleContent r)
    {
       if (!content.contains(r))
       {
          content.add(r);
          repaint();
       }
    }

    /**
     * Clear this Visualization of all SimpleContent objects
     */
    public void clear()
    {
       content.clear();
    }

    /**
     * Get an Iterator that contains all of the SimpleContent
     * objects
     *
     * @return   The SimpleContent objects
     */
    public Iterator<SimpleContent> iterator()
    {
       return content.iterator();       
    }


    /**
     * Remove the given SimpleContent from this Canvas
     *
     * @param r    The SimpleContent to remove
     */
    public void remove(SimpleContent r)
    {
       if (content.remove(r)) repaint();
    }
        

javaexamples/visual/Visualization.java (Fragment: move)

    /**
     * Move the given SimpleContent to the "back"
     *
     * Note: The SimpleContent must have already been added for this
     * method to have an effect.
     *
     * @param r   The SimpleContent to move to the back
     */
    public void toBack(SimpleContent r)
    {
       boolean         removed;
       
       removed = content.remove(r);
       if (removed)
       {
          content.add(r);
       }
    }

    /**
     * Move the given SimpleContent to the "front".
     *
     * Note: The SimpleContent must have already been added for this
     * method to have an effect.
     *
     * @param r   The SimpleContent to move to the front
     */
    public void toFront(SimpleContent r)
    {
       boolean         removed;
       
       removed = content.remove(r);
       if (removed)
       {
          content.add(0, r);
       }
    }
        

View Management:

javaexamples/visual/Visualization.java (Fragment: views)

    /**
     * Add a view to this Visualization
     *
     * @param view    The view to add
     */
    public void addView(VisualizationView view)
    {
       views.addLast(view);       
    }

    /**
     * Get the "main" view (i.e., the "main" VisualizationView
     * that is used to present the SimpleContent objects) associated
     * with this Visualization.
     *
     * Note: A visualization can actually have multiple
     *       views associated with it.  This is a convenience
     *       method that can be used when there is only one such
     *       view.
     *
     * @return   The view
     */
    public VisualizationView getView()
    {
       return views.getFirst();       
    }



    /**
     * Get all of the views associated with this Visualization
     *
     * @return   The views
     */
    public Iterator<VisualizationView> getViews()
    {
       return views.iterator();       
    }

    /**
     * Remove a view from this Visualization
     *
     * @param view    The view to remove
     */
    public void removeView(VisualizationView view)
    {
       views.remove(view);       
    }

    /**
     * Change the "main" view associated with this Visualization
     *
     * Note: A visualization can actually have multiple
     *       views associated with it.  This is a convenience
     *       method that can be used when there is only one such
     *       view.
     *
     * @param view   The new view to use as the "main" view
     */
    public void setView(VisualizationView view)
    {
       views.removeFirst();
       views.addFirst(view);       
    }
        

Forcing Rendering:

javaexamples/visual/Visualization.java (Fragment: repaint)

    /**
     * Repaint the view(s) assocaited with this Visualization
     */
    protected  void repaint()
    {
       Iterator<VisualizationView>   i;       
       VisualizationView             view;
       
       i = views.iterator();
       while (i.hasNext())
       {
          view = i.next();
          view.repaint();
       }
    }
        

The VisualizationView Class

Skeleton:

javaexamples/visual/VisualizationView.java (Fragment: skeleton)

package visual;


import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

import visual.statik.*;

/**
 * A GUI component that presents a collection of SimpleContent
 * objects
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class      VisualizationView
       extends    JComponent
       implements MouseListener
{

    protected Visualization         model;
    protected VisualizationRenderer renderer;
    

    /**
     * Explicit Value Constructor
     *
     * @param model     The Visualization to use
     * @param renderer  The VisualizationRenderer to use
     */
    public VisualizationView(Visualization         model,
                             VisualizationRenderer renderer)
    {
       super();
       this.model    = model;       
       this.renderer = renderer;       

    }

    /**
     * Handle updates
     *
     * This is overriden so that the background is not
     * erased before painting (which is the default)
     */
    public void update(Graphics g)
    {
       paint(g);
    }

    
}
        

Rendering:

javaexamples/visual/VisualizationView.java (Fragment: render)

    /**
     * Set the VisualizationRenderer that this component
     * should use when rendering
     *
     * @param renderer  The VisualizationRenderer
     */
    public void setRenderer(VisualizationRenderer renderer)
    {
       this.renderer = renderer;       
    }
    

    
    /**
     * Operations to perform after rendering.
     * This method is called by paint().
     *
     * @param g   The rendering engine
     */
    protected void postRendering(Graphics g)
    {
       renderer.postRendering(g, model, this);
    }
    

    /**
     * Operations to perform before rendering.
     * This method is called by paint().
     *
     * @param g   The rendering engine
     */
    protected void preRendering(Graphics g)
    {
       renderer.preRendering(g, model, this);
    }
    

    /**
     * Render the content contained in the model.
     * This method is called by paint().
     *
     * @param g   The rendering engine
     */
    protected void render(Graphics g)
    {
       renderer.render(g, model, this);
    }
        

The PlainVisualizationRenderer Class

javaexamples/visual/PlainVisualizationRenderer.java (Fragment: render)

    /**
     * Render the content contained in the model.
     * This method is called by paint().
     *
     * @param g   The rendering engine
     */
    public void render(Graphics          g,
                       Visualization     model,
                       VisualizationView view)
    {

       Iterator<SimpleContent>   iter;
       SimpleContent             c;

       iter = model.iterator();
       while (iter.hasNext())
       {
          c  = iter.next();
          if (c != null) c.render(g);
       }
    }
        

The ScaledVisualizationRenderer Class

Skeleton:

javaexamples/visual/ScaledVisualizationRenderer.java (Fragment: skeleton)

package visual;

import java.awt.*;
import java.util.*;


/**
 * A decorator of a VisualizationRenderer that adds
 * scaling capabilities.  That is, a ScaledVisualizationRenderer
 * will scale all of the content to fit its component.
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class      ScaledVisualizationRenderer
       implements VisualizationRenderer
{
    private double                  height, scaleX, scaleY, width;       
    private VisualizationRenderer   decorated;
    

    /**
     * Explicit Value Constructor
     *
     * @param decorated  The VisualizatioRenderer to decorate
     * @param width      The full-size width of the content
     * @param height     The full-size height of the content
     */
    public ScaledVisualizationRenderer(VisualizationRenderer decorated,
                                       double width, double height)
    {
       this.decorated = decorated;       
       this.width     = width;
       this.height    = height;       
    }
    

    /**
     * Render the content contained in the model.
     *
     * @param g      The rendering engine
     * @param model  The Visualization containing the content
     * @param view   The component presenting the content
     */
    public void render(Graphics          g,
                       Visualization     model,
                       VisualizationView view)
    {
       decorated.render(g, model, view);       
    }
}
        

Before Rendering:

javaexamples/visual/ScaledVisualizationRenderer.java (Fragment: preRendering)

    

    /**
     * Operations to perform before rendering.
     *
     * @param g      The rendering engine
     * @param model  The Visualization containing the content
     * @param view   The component presenting the content
     */
    public void preRendering(Graphics          g,
                             Visualization     model,
                             VisualizationView view)
    {
       Dimension         size;       
       Graphics2D        g2;
       
       

       g2   = (Graphics2D)g;       
       size = view.getSize();
       scaleX = size.getWidth()  / width;
       scaleY = size.getHeight() / height;

       g2.scale(scaleX, scaleY);

       decorated.preRendering(g, model, view);       
    }
        

After Rendering:

javaexamples/visual/ScaledVisualizationRenderer.java (Fragment: postRendering)

    
    /**
     * Operations to perform after rendering.
     *
     * @param g      The rendering engine
     * @param model  The Visualization containing the content
     * @param view   The component presenting the content
     */
    public void postRendering(Graphics          g,
                              Visualization     model,
                              VisualizationView view)
    {
       Graphics2D   g2;
       
       g2 = (Graphics2D)g;       
       g2.scale(1.0/scaleX, 1.0/scaleY);

       decorated.postRendering(g, model, view);       
    }
        

The PartialVisualizationRenderer Class

Skeleton:

javaexamples/visual/PartialVisualizationRenderer.java (Fragment: skeleton)

package visual;

import java.awt.*;
import java.util.*;

/**
 * A decorator of a VisualizationRenderer that 
 * only shows part of the content.
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class      PartialVisualizationRenderer
       implements VisualizationRenderer
{
    private double                  x, y;       
    private VisualizationRenderer   decorated;
    

    /**
     * Explicit Value Constructor
     *
     * @param decorated  The VisualizatioRenderer to decorate
     * @param x          The left-most point to render
     * @param y          The upper-most point to render
     */
    public PartialVisualizationRenderer(VisualizationRenderer decorated,
                                        double x, double y)
    {
       this.decorated = decorated;       
       this.x         = x;
       this.y         = y;       
    }

    /**
     * Render the content contained in the model.
     *
     * @param g      The rendering engine
     * @param model  The Visualization containing the content
     * @param view   The component presenting the content
     */
    public void render(Graphics          g,
                       Visualization     model,
                       VisualizationView view)
    {
       decorated.render(g, model, view);       
    }
}
        

Before Rendering:

javaexamples/visual/PartialVisualizationRenderer.java (Fragment: preRendering)

    

    /**
     * Operations to perform before rendering.
     *
     * @param g      The rendering engine
     * @param model  The Visualization containing the content
     * @param view   The component presenting the content
     */
    public void preRendering(Graphics          g,
                             Visualization     model,
                             VisualizationView view)
    {
       Graphics2D   g2;
       
       g2 = (Graphics2D)g;       
       g2.translate(-x, -y);
       decorated.preRendering(g, model, view);
    }
        

After Rendering:

javaexamples/visual/PartialVisualizationRenderer.java (Fragment: postRendering)

    
    /**
     * Operations to perform after rendering.
     *
     * @param g      The rendering engine
     * @param model  The Visualization containing the content
     * @param view   The component presenting the content
     */
    public void postRendering(Graphics          g,
                              Visualization     model,
                              VisualizationView view)
    {
       Graphics2D   g2;
       
       g2 = (Graphics2D)g;       
       g2.translate(x, y);
       decorated.postRendering(g, model, view);       
    }
        

• An Additional Requirement:
  • The ability to transform content
• Alternative Designs:
  • Add a Transformation class that contains the necessary attributes and behaviors
  • Add the necessary attributes and behaviors to implementations of SimpleContent

Adding Transformations using a Helper

Adding Transformations using Stand-Alone Interfaces

Adding Transformations using Individual Interfaces

The Best Way to Add Transformations

The AbstractTransformableContent Class

javaexamples/visual/statik/AbstractTransformableContent.java

package visual.statik;

import java.awt.geom.*;


/**
 * A partial implementation of the TransformableContent
 * interface that keeps track of transformation information
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public abstract class AbstractTransformableContent 
                implements TransformableContent
{

    protected boolean          relocated, rerotated, rescaled;
    protected double           angle;
    protected double           xScale, yScale;
    protected double           x, y;    
    protected double           xRotation, yRotation;    


    /**
     * Default Constructor
     */
    public AbstractTransformableContent()
    {
       setTransformationRequired(false);
       
       angle     = 0.0;
       xScale    = 1.0;
       yScale    = 1.0;
       x         = 0.0;
       y         = 0.0;
       xRotation = 0.0;
       yRotation = 0.0;
    }

    /**
     * Get the (concatenated) AffineTransform
     *
     * @return  The rotation, scaling and translation concatenated
     */
    protected AffineTransform getAffineTransform()
    {
       // We could use an object pool rather than local 
       // variables.  Rough tests estimate that this method 
       // would require 1/3 as much time with an object pool.
       AffineTransform     at, rotation, scaling, translation;
       Rectangle2D         bounds;

       // Start with the identity transform
       at = AffineTransform.getTranslateInstance(0.0, 0.0);

       if (rerotated)
       {
          bounds = getBounds2D(false);
          
          
          rotation = AffineTransform.getRotateInstance(angle, 
                                                   xRotation,
                                                   yRotation);
          at.preConcatenate(rotation);
       }

       
       if (rescaled)
       {          
          scaling = AffineTransform.getScaleInstance(xScale, 
                                                     yScale);
          at.preConcatenate(scaling);
       }
       

       if (relocated)
       {
          translation = AffineTransform.getTranslateInstance(x, 
                                                             y);
          at.preConcatenate(translation);
       }

       return at;
    }
    
    /**
    * Returns a high precision bounding box of the appropriately
    * transformed content (required by TransformedContent) 
    *
    * @return   The bounding box
    */
    public Rectangle2D getBounds2D()
    {
       return getBounds2D(true);       
    }
    

   
    /**
     * Returns a high precision bounding box of the Content
     * either before or after it is transformed
     *
     * @param    transformed    true to get the BB of the transformed content
     * @return   The bounding box
     */
    public abstract Rectangle2D getBounds2D(boolean transformed);
       

    /**
     * Set the translation
     * (required by TransformedContent)
     *
     * @param x   The x posiiton
     * @param y   The y position
     */
    public void setLocation(double x, double y)
    {
       this.x = x;
       this.y = y;
       relocated = true;       
    }


    /**
     * Set the angle of rotation around the midpoint
     * (required by TransformedContent)
     *
     * @param angle   The rotation angle
     * @param x       The x-coordinate of the point to rotate around
     * @param y       The y-coordinate of the point to rotate around
     */
    public void setRotation(double angle, double x, double y)
    {
       this.angle = angle;
       xRotation  = x;
       yRotation  = y;       
       rerotated  = true;       
    }
    

    /**
     * Set the scaling
     * (required by TransformedContent)
     *
     * @param xScale   The scaling in the horizontal dimension
     * @param yScale   The scaling in the vertical  dimension
     */
    public void setScale(double xScale, double yScale)
    {
       this.xScale = xScale;
       this.yScale = yScale;
       rescaled    = true;       
    }
    

    /**
     * Set the scaling
     *
     * @param scale   The scaling (in both dimensions)
     */
    public void setScale(double scale)
    {
       setScale(scale, scale);
    }


    /**
     * Set whether this AbstractTransformableContent object
     * needs to be transformed before being used
     *
     * @param required   true to indicate that a transformation is requried
     */
    protected void setTransformationRequired(boolean required)
    {
       relocated = required;
       rerotated = required;
       rescaled  = required;
    }
    

    /**
     * Does this AbstractTransformableContent object need
     * to be transformed before being used?
     *
     * @return  true to indicate a transformation is required
     */
    protected boolean isTransformationRequired()
    {
       return (relocated || rerotated || rescaled);
    }
    
}