dda line drawing algorithm in java

Read about DDA (Digital differential analyzer) algorithm.

You can find line drawing using bresenham's line algorithm here.

Java Code for DDA line drawing algorithm. :-


package applet;

import java.applet.Applet;
import java.awt.Button;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

public class dda extends Applet implements MouseListener, MouseMotionListener, ActionListener {
    int x1 = -1, y1 = -1, x2 = -1, y2 = -1,     //coordinates of start and end points
            pixelsize = 12,                     //size of pixel in raster
            xa = 0, xfin = 0, yfin = 0,         //increment and end point coordinates used in animation
            dif = 0;                            //increment on main axis
    Button refresh = new Button("   CLEAN   "); //button used to reset the drawing
    boolean drawLine = true, animate = false,   //vars to indicate the state of similarly named check boxes
            inProgress = false,                 //var used to indicate if the animation is in progress
            steep = false;                      //var used in animation
    volatile Thread vlakno;                     //thread used for animation
    double ya = 0, ma = 0;                      //vars used in animation
 
    public void setpix(int x, int y, int c) {   //draws a square on selected coordinates in raster
        Graphics g = getGraphics();
        g.setColor(new Color(c));
        g.fillRect(pixelsize * x, pixelsize * y, pixelsize, pixelsize);
    }
 
    public void rasterline(int xi, int yi, int xf, int yf) {
        //this method rasterizes the line if X shall be the main axis
        double y = yi;
        double m = (double)(yf - yi) / (xf - xi);   //calculates the direction
        if (Math.abs(m) <= 1) {                     //true if X is the main axis
            if (xi > xf) {                          //sets increment on the main (i.e. X) axis
                dif = -1;
            } else {
                dif = 1;
            }
            Graphics g = getGraphics();
            int strpos = 35;        //the following lines draws an info about the line and increments
            g.drawString("Real Coordinates", 10, 300 + strpos); strpos+=15;
            g.drawString("Start Point (real): [" + x1 + ", " + y1 + "]", 10, 300 + strpos); strpos+=15;
            g.drawString("End Point (real): [" + x2 + ", " + y2 + "]", 10, 300 + strpos); strpos+=25;
            g.drawString("Raster Coordinates", 10, 300 + strpos); strpos+=15;
            g.drawString("Start Point (raster): [" + xi + ", " + yi + "]", 10, 300 + strpos); strpos+=15;
            g.drawString("End Point (raster): [" + xf + ", " + yf + "]", 10, 300 + strpos); strpos+=25;
            g.drawString("Increment on X-axis = " + dif, 10, 300 + strpos); strpos+=15;
            if (xi > xf) {  //true if start point is to the right of the end point
                g.drawString("Increment on Y-axis = " + (double)Math.round(m*100)/100, 10, 300 + strpos); strpos+=15;
                g.setColor(new Color(0xFF0055));
                g.drawLine(645, 400, 645 + dif*50, 400 - (int)(m*50));
                g.fillOval(645 + dif*50 - 5, 400 - (int)(m*50) - 5, 10, 10);
                g.setColor(new Color(0x000000));
                for (int i = xi; i >= xf; i+=dif) {             //the line rasterization itself
                    setpix(i, (int)Math.round(y), 0x000000);
                    y -= m;
                }
            } else {    //if the start point is to the left of the end point
                //works the same way as the statement before, only increment on y axis is inverted
                //(and the for condition is adjusted to work properly)
                g.drawString("Increment on Y-axis = " + (double)Math.round(-m*100)/100, 10, 300 + strpos); strpos+=15;
                g.setColor(new Color(0xFF0055));
                g.drawLine(645, 400, 645 + dif*50, 400 + (int)(m*50));
                g.fillOval(645 + dif*50 - 5, 400 + (int)(m*50) - 5, 10, 10);
                g.setColor(new Color(0x000000));
                for (int i = xi; i <= xf; i+=dif) {
                    setpix(i, (int)Math.round(y), 0x000000);
                    y += m;
                }
            }
        } else {
            //if Y shall be the main axis, the call thes metho instead
            rastersteepline(yi, xi, yf, xf);
        }
    }
 
    public void rastersteepline(int xi, int yi, int xf, int yf) {
        //this method rasterizes the line if Y shall be the main axis
        //works similarly as the rasterline method, just swaps the main axis
        if (xi > xf) {  //sets the increment on main (i.e. Y) axis
            dif = -1;
        } else {
            dif = 1;
        }
        double y = yi;
        double m = (double)(yf - yi) / (xf - xi);   //calculates the direction
        Graphics g = getGraphics();
        int strpos = 35;        //the following lines draws an info about the line and increments
        g.drawString("Real Coordinates", 10, 300 + strpos); strpos+=15;
        g.drawString("Start Point: [" + x1 + ", " + y1 + "]", 10, 300 + strpos); strpos+=15;
        g.drawString("End Point: [" + x2 + ", " + y2 + "]", 10, 300 + strpos); strpos+=25;
        g.drawString("Raster Coordinates", 10, 300 + strpos); strpos+=15;
        g.drawString("Start Point: [" + xi + ", " + yi + "]", 10, 300 + strpos); strpos+=15;
        g.drawString("End Point: [" + xf + ", " + yf + "]", 10, 300 + strpos); strpos+=25;
        if (xi > xf) {  //true if start point is to the right of the end point
            g.drawString("Increment on X-axis = " + (double)Math.round(-m*100)/100, 10, 300 + strpos); strpos+=15;
            g.setColor(new Color(0xFF0055));
            g.drawLine(645, 400, 645 - (int)(m*50), 400 + dif*50);
            g.fillOval(645 - (int)(m*50) - 5, 400 + dif*50 - 5, 10, 10);
            g.setColor(new Color(0x000000));
            for (int i = xi; i >= xf; i+=dif) {
                setpix((int)Math.round(y), i, 0x000000);
                y -= m;
            }
        } else {        //if start point is to the left of the end point
            g.drawString("Increment on X-axis = " + (double)Math.round(m*100)/100, 10, 300 + strpos); strpos+=15;
            g.setColor(new Color(0xFF0055));
            g.drawLine(645, 400, 645 + (int)(m*50), 400 + dif*50);
            g.fillOval(645 + (int)(m*50) - 5, 400 + dif*50 - 5, 10, 10);
            g.setColor(new Color(0x000000));
            for (int i = xi; i <= xf; i+=dif) {
                setpix((int)Math.round(y), i, 0x000000);
                y += m;
            }
        }
        g.drawString("Increment on Y-axis = " + -dif, 10, 300 + strpos); strpos+=15;
    }
 
    public void init() {
        //sets up the environment
        setSize(800, 500);
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
     
        refresh.addActionListener(this);
        this.add(refresh);
      }
 
    public void stop() {
        vlakno = null;
    }
 
    public void update(Graphics g) {
        //overrides the default update method that is called after aplication of repaint() command
        //this disables the pre-cleaning of the drawing area before the paint method is applied
        //that causes the flicker
        paint(g);
    }
 
    public void paint( Graphics g ) {
        Dimension d = getSize();
        Color c1 = new Color(0x000000);
        Color c2 = new Color(0xCCCCCC);
        Color c3 = new Color(0xF5C24E);

        refresh.setLocation(380, 353);
        g.drawString("Raster Size:", 225, 370);

        //draws the mini coordinate system in right-bottom corner
        if (!inProgress) {
            g.drawLine(570, 400, 720, 400);
            g.drawLine(645, 325, 645, 475);
            g.drawLine(570, 325, 720, 475);
            g.drawLine(570, 475, 720, 325);
        }
     
        if ((x1 >= 0) && (y1 >= 0) && (x2 >= 0) && (y2 >= 0)) {
        //true if both the start and end point were selected
            if(inProgress) {    //true if the animation is in progress
                if(steep) {     //true if Y is the main axis
                    setpix((int)Math.round(ya), xa, 0xA6EBFB);
                } else {
                    setpix(xa, (int)Math.round(ya), 0xA6EBFB);
                }
            } else {    //if the animation is not in progress
                rasterline(x1 / pixelsize, y1 / pixelsize, x2 / pixelsize, y2 / pixelsize);
            }
         
            if(drawLine) {  //draws the "real" line, if drawLineCHX checkbox is checked
                g.setColor(c3);
                g.drawLine(x1, y1, x2, y2);
            }
        }
     
        g.clearRect(1, 301, d.width - 1, 20);

        //these following lines draws the raster lines
        g.setColor(c2);
        for(int i = pixelsize; i < d.width; i += pixelsize) {
            g.drawLine(i, 0, i, d.height - 200);
        }
        for(int i = pixelsize; i < d.height - 200; i += pixelsize) {
            g.drawLine(0, i, d.width, i);
        }
     
        g.setColor(c1);
        //draws the text in the mini coordinate system in right-bottom corner
        g.drawString("dx=1/m", 595, 320); g.drawString("dy=1", 595, 330);
        g.drawString("dx=1/m", 665, 320); g.drawString("dy=1", 665, 330);
        g.drawString("dx=1", 705, 370); g.drawString("dy=m", 705, 380);
        g.drawString("dx=1", 705, 430); g.drawString("dy=-m", 705, 440);
        g.drawString("dx=-1/m", 665, 475); g.drawString("dy=-1", 665, 485);
        g.drawString("dx=-1/m", 595, 475); g.drawString("dy=-1", 595, 485);
        g.drawString("dx=-1", 555, 430); g.drawString("dy=-m", 555, 440);
        g.drawString("dx=-1", 555, 370); g.drawString("dy=m", 555, 380);
     
        //these following lines draws the border lines
        g.drawLine(0, 0, d.width, 0);
        g.drawLine(0, 0, 0, d.height);
        g.drawLine(d.width - 1, d.height - 1, d.width - 1, 0);
        g.drawLine(d.width - 1, d.height - 200, 0, d.height - 200);
        g.drawLine(d.width - 1, d.height - 1, 0, d.height - 1);
    }
 
    public void actionPerformed(ActionEvent e) {
        //a method for the refresh ("CLEAN") buttton
        vlakno = null;      //turn of the animation process
        inProgress = false;
        x1 = -1;            //reset the line coordinates
        y1 = -1;
        x2 = -1;
        y2 = -1;
        Graphics g = getGraphics();
        g.clearRect(0,0, getSize().width, getSize().height);    //clean the drawing area
        repaint();
    }
 
    public void mousePressed(MouseEvent e) {
        if (e.getY() < 300) {            
        //disallows drawing of the line in the lower area, outside the raster
            if ((x1 < 0) || (y1 < 0)) { //if the start point is not set
                x1 = e.getX();
                y1 = e.getY();
                setpix(x1 / pixelsize, y1 / pixelsize, 0x00FF00);
            } else  if (((x2 < 0) || (y2 < 0)) && (e.getX() != x1) && (e.getY() != y1)) {
            //if the end point is not set
                x2 = e.getX();
                y2 = e.getY();
                repaint();
            }
        }
    }
 
    public void mouseDragged(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
    public void mouseClicked(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mouseMoved(MouseEvent e) {}
}

copy this code and run in eclipse using Java applet.