figure.java

java编程的一些Applets例子。值得深入研究一下。

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// $Id: Figure.java,v 1.3 1996/04/16 20:55:23 greg Exp $

import java.lang.*;
import java.awt.*;
import java.io.*;
import java.net.*;

/*

A Figure is a generic line drawing.  It consists of a list of line
segments in the plane.  It can be drawn to a Graphics object
(with transformations), intersected with another Figure, read from a
stream, and written to a stream.

*/

public class Figure
{
    Color color = null;
    int lines[][][];
    int n_lines;

    Figure() {
	this.lines = new int[2][2][2];
	n_lines = 2;
    }

    Figure( int lines[][][] ) {
	this.lines = lines;
	n_lines = lines.length;
    }

    // Translate and rotate the lines.
    public Figure transform( int ox, int oy, double angle ) {
	double s = Math.sin( angle );
	double c = Math.cos( angle );
	int tlines[][][] = new int[n_lines][2][2];
	for (int i=0; i<n_lines; ++i) {
	    int sx=lines[i][0][0], sy=lines[i][0][1];
	    int ex=lines[i][1][0], ey=lines[i][1][1];
	    int sxt = (int)(ox+sx*c-sy*s);
	    int syt = (int)(oy+sx*s+sy*c);
	    int ext = (int)(ox+ex*c-ey*s);
	    int eyt = (int)(oy+ex*s+ey*c);
	    tlines[i][0][0] = sxt;
	    tlines[i][0][1] = syt;
	    tlines[i][1][0] = ext;
	    tlines[i][1][1] = eyt;
	}
	return new Figure( tlines );
    }

    // The default rendering routine is to simply
    // draw all the lines.
    public void render( Graphics g ) {
	if (color != null) g.setColor( color );
	for (int i=0; i<n_lines; ++i)
	  g.drawLine( lines[i][0][0], lines[i][0][1],
		     lines[i][1][0], lines[i][1][1] );
    }

    // display a line.
    void pline( int a[][] ) {
	System.out.println( ""+a[0][0]+" "+a[0][1]+" "+a[1][0]+" "+a[1][1] );
    }

    // intersectLine1() checks for intersection between one line segment and
    // the infinte line containing the other line segment.
    public boolean intersectLine1( int a[][], int b[][] ) {
	int sx=a[0][0], sy=a[0][1], ex=a[1][0], ey=a[1][1];
	return
	  (((sy-ey)*(b[0][0]-sx) + (ex-sx)*(b[0][1]-sy)) > 0) !=
	    (((sy-ey)*(b[1][0]-sx) + (ex-sx)*(b[1][1]-sy)) > 0);
    }

    // intersectLine() checks for intersection between two line segments.
    public boolean intersectLine( int a[][], int b[][] ) {
	if (intersectLine1( a, b ) && intersectLine1( b, a )) {
	    return true;
	}
	return false;
    }

    // Check for intersection between the given line and the lines
    // in this Figure.
    public boolean intersectLines( int b[][] ) {
	for (int i=0; i<n_lines; ++i)
	  if (intersectLine( lines[i], b ))
	    return true;
	return false;
    }

    // Check for intersection between the given Figure and us.
    public boolean intersectFigure( Figure f ) {
	for (int i=0; i<f.n_lines; ++i)
	  if (intersectLines( f.lines[i] ))
	    return true;
	return false;
    }

    // Clear out all the lines.
    public void reset() {
	n_lines = 0;
    }

    // Add a line, extending the array if necessary
    public void addLine( int sx, int sy, int ex, int ey ) {
	if (n_lines >= lines.length) {
	    int newlines[][][] = new int[lines.length*2][2][2];
	    for (int i=0; i<lines.length; ++i)
	      newlines[i] = lines[i];
	    lines = newlines;
	}
	lines[n_lines][0][0] = sx;
	lines[n_lines][0][1] = sy;
	lines[n_lines][1][0] = ex;
	lines[n_lines][1][1] = ey;
	n_lines++;
    }

    // Remove a line.
    public void removeLine( int which ) {
	int tmp[][] = lines[which];
	lines[which] = lines[--n_lines];
	lines[n_lines] = tmp;
    }

    // Calculate the distance between two points.
    double dist( double x0, double y0, double x1, double y1 ) {
	x1 -= x0; y1 -= y0;
	return Math.sqrt( x1*x1 + y1*y1 );
    }

    // Calculate the distance from (x,y) to line.
    double distToLine( double x, double y, int line[][] ) {
	if ((line[1][0]-line[0][0])*(x-line[0][0])
	    + (line[1][1]-line[0][1])*(y-line[0][1]) < 0) {
	    return dist( x, y, (double)line[0][0], (double)line[0][1] );
	}
	else if ((line[0][0]-line[1][0])*(x-line[1][0])
		 + (line[0][1]-line[1][1])*(y-line[1][1]) < 0) {
	    return dist( x, y, (double)line[1][0], (double)line[1][1] );
	}
	else {
	    int ax = line[1][0] - line[0][0];
	    int ay = line[1][1] - line[0][1];
	    double bx = x - line[0][0];
	    double by = y - line[0][1];
	    return Math.abs( (-ay*bx + ax*by)/Math.sqrt(ax*ax+ay*ay) );
	}
    }

    // Find the nearest line in this figure to (x,y).
    public int nearestLine( double x, double y ) {
	int best=0;
	double dist = distToLine( x, y, lines[0] );

	for (int i=0; i<n_lines; ++i) {
	    double d = distToLine( x, y, lines[i] );

	    if (best==-1 || d<dist) {
		best = i;
		dist = d;
	    }
	}
	return best;
    }

    // Write this Figure to a stream.
    public void write( DataOutputStream out ) throws IOException {
	out.writeInt( n_lines );
	for (int i=0; i<n_lines; ++i) {
	    out.writeInt( lines[i][0][0] );
	    out.writeInt( lines[i][0][1] );
	    out.writeInt( lines[i][1][0] );
	    out.writeInt( lines[i][1][1] );
	}
    }

    // Write this Figure to a file.
    public void write( String fname ) {
	try {
	    FileOutputStream fout = new FileOutputStream( fname );
	    DataOutputStream out = new DataOutputStream( fout );
	    write( out );
	    fout.close();
	    System.out.println( "Wrote." );
	} catch( Exception e ) {
	    System.out.println( "Write: " + e );
	}
    }

    // Read this Figure from a stream.
    public void read( DataInputStream in ) throws IOException {
	reset();
	int n = in.readInt();
	for (int i=0; i<n; ++i) {
	    int sx = in.readInt();
	    int sy = in.readInt();
	    int ex = in.readInt();
	    int ey = in.readInt();
	    addLine( sx, sy, ex, ey );
	}
    }

    // Read this Figure from a file.
    public void read( String fname ) {
	try {
	    FileInputStream fin = new FileInputStream( fname );
	    DataInputStream in = new DataInputStream( fin );
	    read( in );
	    System.out.println( "Read." );
	    fin.close();
	} catch( Exception e ) {
	    System.out.println( "Read: " + e );
	}
    }

    // Read this Figure from a URL.
    public void read( URL url ) {
	try {
	    URLConnection uc = url.openConnection();
	    InputStream in = uc.getInputStream();
	    read( new DataInputStream( in ) );
	} catch( IOException e ) {
	    System.out.println( "read " + e );
	}
    }
}