Transcript Shapes in 2D Graphics

Shapes in 2D Graphics
Objectives
To give an overview on the Java classes for Graphics.
To present the main classes of java.awt.geom:
Point2D, Line2D, Rectangle2D,…
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Graphics, Graphics2D, Geom
Class Graphics (java.awt.*)
- JDK 1.1.
- base class for Graphics2D.
- basic methods (drawing, filling,…) for working with shapes, images.
Graphics2D Class (java.awt)
- extends Graphics; any method from Graphics can be used.
- offers a diversity of methods to for working shapes, transformations, colours
- fundamental class for rendering shapes, texts,…
java.awt.geom package
- provides classes for working with geometrical objects in 2D graphics.
- Point2D + (Line2D, Rectangle2D, Arc2D, Ellipse2D,…)
- coordinates real by using inner classes (Double, Float) in each class.
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Point2D
Point2D offers points in real coordinates.
Abstract class with inner classes Double, Float.
Construct a point:
double coordinates: Point2D p = new Point2D.Double();
Point2D p = new Point2D.Double(x,y);
float coordinates: Point2D p = new Point2D.Float();
Point2D p = new Point2D.Float(x,y);
Gives methods for:
- get/set the point location:
p.getX(), p.getY(), p.setLocation(x,y), p.setLocation(p1),
- find the distance between the point p and another point.
p.distance(x,y), p.distance(p1), Point2D.distance(p1,p2)
See the class’ methods.
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Point2D: Example
import java.applet.*;
import java.awt.*;
import java.awt.geom.*;
public class L8Appl1 extends Applet {
Point2D p1,p2; // declare two double points
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D)g; // convert g to a Graphics2D
// construct p1 and p2
p1 = new Point2D.Double(100.,100.); g2.drawString(“P1”,100,102);
p2 = new Point2D.Double(200.,200.); g2.drawString(“P2”,200,202);
g2.draw(new Line2D.Double(p1.getX(),p1.getY(),p2.getX(),p2.getY())); // draw a line from p1 to p2
double lenght=p1.distance(p2); // find the distance between p1 and p2.
g.drawString("The distance is : " + lenght,20,20); // write the distance
}
}
Remark: length is also given by Point2D.distance(p1,p2)
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Line2D
Line2D offers lines with real coordinates.
Abstract class with two inner classes: Double and Float.
Construct lines as follows:
Line2D line = new Line2D.Double();
Line2D line = new Line2D.Double(p1,p2);
Line2D line = new Line2D.Double(x1,y1,x2,y2);
Similarly for float.
Offer method for:
- get/set methods: coordinates
- contains methods: test if the line contains a point or is contained by a
rectangle.
- intersects methods: test if the line is intersected by another line or
rectangle.
- distance methods: from a point to the line.
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Line2D: Example
import java.applet.*;
import java.awt.*;
import java.awt.geom.*;
public class L8Appl2 extends Applet {
Line2D l1= new Line2D.Double(), l2= new Line2D.Double(); // construct two lines
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
l1.setLine(50,50,200,200);l2.setLine(200,50,50,200); // set the lines
g2.draw(l1);g2.draw(l2); // draw the lines !!!
if(l1.intersectsLine(l2))g2.drawString("Intersected lines",10,10); // if l1 and l2 are intersected
else g2.drawString("Disjoint lines",10,10);
}
}
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Rectangle2D
Class RectangularShape is the base for:
Rectangle2D, RoundRectangle2D, Arc, Ellipse.
Rectangle2D has two inner classes: Double, Float.
Construct rectangles as follows:
Rectangle2D r = new Rectangle2D.Double();
Rectangle2D r = new Rectangle2D.Double(x,y,w,h);
Methods for:
get / set the elements x,y,w,h.
find if the rectangle contains a point or is contained in another
rectangle
intersection with a line or with another rectangle
union with another rectangle.
Remark: RoundRectangle2D is similar.
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import java.applet.*;
import java.awt.*;
import java.awt.geom.*;
public class L8Appl3 extends Applet {
Rectangle2D r1,r2,r3; // Declare three rectangles
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
r1 = new Rectangle2D.Double(100,100,200,100); // Construct two rectangles
r2 = new Rectangle2D.Double(150,150,200,100);
r3 = new Rectangle2D.Double(); // construct an empty rectangle
g.setColor(Color.red);g2.draw(r1); g.setColor(Color.blue);g2.draw(r2);
if(r1.intersects(r2.getX(),r2.getY(),r2.getWidth(),r2.getHeight())){
// find is r1 intersects r2
Rectangle2D.intersect(r1,r2,r3);
g.setColor(Color.black);g2.draw(r3);
}
}
}
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Lines, Rectangles, … = Shapes
A continuous sequence of lines, quadratic and cubic curves presents a shape.
Lines, Rectangles, … are shapes.
Interface Shape represents the support for all the geom classes.
Abstract methods for:
get the bound of the shape. (the rectangle that contains the shape.)
contains methods. (a point is the shape or the shape is in a rectangle.)
intersects methods. (if the shape intersects an rectangle.)
working with PathIterator. (the shape’s boundary.)
Graphics2D draws shapes: g2.draw(shape).
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PathIterator Interface
PathIterator: traverse and identify each component of a path.
The Nature of a component:
SEG_MOVETO,SEG_LINETO, SEG_QUADTO,
SEG_CUBICTO, SEG_CLOSETO.
Methods:
currentSegment(coordinates) – return the nature of the segment and its
coordinates in float or double.
next() – move the pathiterator forward by one segment.
isDone() – find if the pathiterator is done.
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Construct a General Path
The GeneralPath Class helps to create a shape as a sequence of segments.
Methods to add segments to the GeneralPath.
moveTo(x,y) – move the current path without drawing
lineTo(x,y) – draw a line to (x,y)
quadTo(x1,y1,x2,y2) – draw a quadratic curve to (x1,y1).
curveTo(x1,y1,x2,y2,x3,y3) - draw a cubic curve to (x1,y1).
Append to the general path a shape or a pathiterator.
contains and intersects methods with a point and with a rectangle.
get methods for the current point of the bounds.
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import java.applet.*;
import java.awt.*;
import java.awt.geom.*;
public class L8Appl4 extends Applet {
GeneralPath path = new GeneralPath(); // declare a GeneralPath
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
construct(200,200,5,100); g2.draw(path);
}
public void construct(float x0,float y0,int n,float r){
float x [] = new float [n];float y [] = new float [n]; // construct the coordinates arrays
for(int i=0;i<n;i++){ // find the coordinates based on the general equation
x[i]=x0+(float)(r*Math.cos(2*i*Math.PI/n)); y[i]=x0+(float)(r*Math.sin(2*i*Math.PI/n));
}
path.moveTo(x[0],y[0]);
// go to the first point of the line
for(int i=0;i<n;i++)path.lineTo(x[(i+1)%n],y[(i+1)%n]); // add to the shape the segments one by one
}
}
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The Area Class
Area Class provides methods for combining shapes. (Implement Shape.)
The main operations: union, intersection, subtraction, exclusive or.
Constructing Area
Area ar = new Area(); - empty area
Area ar = new Area(Shape sh); - area for the interior of sh
Methods for
add(ar) – add the area sh to the current area.
intersect(sh) - intersect the area sh to the current area.
subtract(sh) - subtract the area sh to the current area.
Methods inherited from Shape: draw, fill, contains, intersects,…
.
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import java.applet.*;
import java.awt.*;
import java.awt.geom.*;
public class L8Appl5 extends Applet {
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
g.setColor(Color.blue);g.fillRect(0,0,500,500);g.setColor(Color.yellow);
Area area1 = new Area (new Ellipse2D.Double(50,50,200,100));
Area area2 = new Area (new Ellipse2D.Double(100,100,100,200));
area1.add(area2);g2.fill(area1);
}
}
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Problems To Solve
1.
Generate n random lines and find how many intersections points are found.
6 intersection points for the above example.
2.
Generate n random rectangles and find the area covered by them.
To Read: Jonathan Knudsen, Java 2D Graphics, chapter 3.
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