12.6 Stroking Lines

The BasicStroke class is an implementation of the Stroke interface. This interface is responsible for defining how lines are drawn, or stroked, in Java 2D. Filling arbitrary shapes is the fundamental graphics operation defined by Java 2D. The Stroke interface defines the API by which line-drawing operations are transformed into area-filling operations, as illustrated in Figure 12-7. Example 12-9 shows the code used to produce this figure. (Once you understand how the Stroke interface converts a shape to a stroked shape suitable for filling, you can define interesting custom Stroke implementations, as we'll do later in this chapter, in Example 12-17.)

Figure 12-7. How lines are drawn in Java 2D

Example 12-9. Stroking.java

package je3.graphics;
import java.awt.*;
import java.awt.geom.*;

/** A demonstration of how Stroke objects work */
public class Stroking implements GraphicsExample {
    static final int WIDTH = 725, HEIGHT = 250;  // Size of our example
    public String getName( ) {return "Stroking";} // From GraphicsExample
    public int getWidth( ) { return WIDTH; }      // From GraphicsExample
    public int getHeight( ) { return HEIGHT; }    // From GraphicsExample

    /** Draw the example */
    public void draw(Graphics2D g, Component c) {
        // Create the shape we'll work with.  See convenience method below.
        Shape pentagon = createRegularPolygon(5, 75);

        // Set up basic drawing attributes
        g.setColor(Color.black);                          // Draw in black
        g.setStroke(new BasicStroke(1.0f));               // Use thin lines
        g.setFont(new Font("SansSerif", Font.PLAIN, 12)); // Basic small font

        g.translate(100, 100);                        // Move to position
        g.draw(pentagon);                             // Outline the shape
        g.drawString("The shape", -30, 90);           // Draw the caption

        g.translate(175, 0);                          // Move over
        g.fill(pentagon);                             // Fill the shape
        g.drawString("The filled shape", -50, 90);    // Another caption

        // Now use a Stroke object to create a "stroked shape" for our shape
        BasicStroke wideline = new BasicStroke(10.0f);
        Shape outline = wideline.createStrokedShape(pentagon);

        g.translate(175, 0);                          // Move over
        g.draw(outline);                              // Draw the stroked shape
        g.drawString("A Stroke creates",-50,90);      // Draw the caption
        g.drawString("a new shape", -35, 105);

        g.translate(175,0);                           // Move over
        g.fill(outline);                              // Fill the stroked shape
        g.drawString("Filling the new shape",-65,90); // Draw the caption
        g.drawString("outlines the old one",-65,105);
    }

    // A convenience method to define a regular polygon.
    // Returns a shape that represents a regular polygon with the specified
    // radius and number of sides, and centered at the origin.
    public Shape createRegularPolygon(int numsides, int radius) {
        Polygon p = new Polygon( );               
        double angle = 2 * Math.PI / numsides;   // Angle between vertices
        for(int i = 0; i < numsides; i++)  // Compute location of each vertex
            p.addPoint((int)(radius * Math.sin(angle*i)),
                       (int)(radius * -Math.cos(angle*i)));
        return p;  
    }
}