Question

I have written a code that draws grids and a triangle inside one grid cell. The grid size is increased/decreased when the window is maximized or minimized.

My requirement is that the triangle size should also increase/decrease to fit the grid cell each time the grid size is increased/decreased.

My code is as follows:

import java.awt.BasicStroke;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.RenderingHints;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class Grid extends JPanel {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Grid g = new Grid();
        JFrame f = new JFrame("Application GUI Window");
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {System.exit(0);}
        });
        f.getContentPane().add("Center", g);
        f.pack();
        f.setSize(new Dimension(450,400));
        f.show();
    }

    public void paint(Graphics g) {

        Graphics2D g2d = (Graphics2D) g;
        Dimension d = getSize();
        g2d.setBackground(getBackground());
        g2d.clearRect(0, 0, d.width, d.height);
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        drawGrid(d.width, d.height, g2d);
        int[] xPoints = {20,15,25}; 
        int[] yPoints = {15,25,25};
        int n = 3;

        Polygon triangle = new Polygon(xPoints, yPoints, n);
        g.fillPolygon(triangle);
    }

    private void drawGrid(int width, int height, Graphics2D g2d) {

       /* BasicStroke border = new BasicStroke(3, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_ROUND, 0, new float[]{0,1,0,1}, 0);
        g2d.setStroke(border);
        g2d.drawRect(3,3,width-6,height-6);*/

        //horizontal lines
        int cellheight = height/10;
        int cellwidth = width/5;
        for (int j=0;j<height;j=j+cellheight)
        {
            BasicStroke line = new BasicStroke(1, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_ROUND, 0, new float[]{0,1,0,1}, 0);
               g2d.setStroke(line);
               g2d.drawLine(0, j, cellwidth*5, j);

        }

        //vertical lines

        for (int i=0;i<width;i=i+cellwidth)
        {
            BasicStroke line = new BasicStroke(1, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_ROUND, 0, new float[]{0,1,0,1}, 0);
               g2d.setStroke(line);
               g2d.drawLine(i, 0, i, cellheight*10);

        }

    }
}

Thanks in advance for your help.

Answer 1

You can tie the coordinates of the triangle to the dimensions of a grid cell. Here is a snippet based on your example:

int cellHeight = d.height/10;
int cellWidth = d.width/5;

int xOffset = cellWidth/6;
int yOffset = cellHeight/6;

int[] xPoints = {cellWidth/2, xOffset, cellWidth - xOffset}; 
int[] yPoints = {yOffset, cellHeight - yOffset, cellHeight - yOffset};

Polygon triangle = new Polygon(xPoints, yPoints, xPoints.length);

Note that in Swing you usually should override paintComponent() rather than paint(), unless in some special cases. See A Closer Look at the Paint Mechanism for more details.

Also note that show() is deprecated in favor of setVisible(). You can replace it with: setVisible(true)