SWT: Working with colors

SWT provides Color class to define colors. There are three ways to get Color object.

a.   Using getSystemColor method

b.   Using RGB

c.    Using RGBA

Using getSystemColor method

Display class provides 'getSystemColor' method to get the color instance.

public Color getSystemColor (int id)

Ex:

Color blue = display.getSystemColor(SWT.COLOR_BLUE);

Using RGB

Color class provides following constructor to define color instance using RGB notation.

public Color (Device device, RGB rgb)

Ex:

Color green = new Color(display, new RGB(0, 255, 0));

Using RGBA

Color class provide following constructor to define color instance using RGBA notation.

public Color(Device device, RGBA rgba)

Ex:

Color color = new Color(display, new RGBA(24, 20, 123, 5));

If you create Color instances using any approach other than getSystemColor method, you need to dispose them manually.

Ex:

green.dispose();

color.dispose();

Following is the complete working application.

package swt_app;

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.RGB;
import org.eclipse.swt.graphics.RGBA;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class Test
{

 private static int shellWidth = 1000;
 private static int shellHeight = 700;

 private static int canvasHeight = 300;
 private static int canvasWidth = 400;

 private static void drawGraphcis(Display display, GC gc)
 {
  Color blue = display.getSystemColor(SWT.COLOR_BLUE);
  Color red = display.getSystemColor(SWT.COLOR_RED);
  Color green = new Color(display, new RGB(0, 255, 0));
  Color color = new Color(display, new RGBA(24, 20, 123, 5));

  gc.setBackground(red);
  gc.drawRectangle(150, 130, 200, 75);
  gc.fillRectangle(30, 30, 200, 75);

  gc.setForeground(blue);
  gc.drawLine(0, 0, 400, 300);

  gc.drawString("Hello World Graphics Application", 75, 0);

  gc.drawOval(0, 0, 400, 300);

  green.dispose();
  color.dispose();

 }

 private static void addGraphicsToShell(Display display, Shell shell)
 {
  Canvas canvas = new Canvas(shell, SWT.BORDER);
  canvas.setSize(canvasWidth, canvasHeight);
  canvas.setLocation(20, 20);

  /* Open shell window */
  shell.open();

  GC gc = new GC(canvas);

  drawGraphcis(display, gc);

  canvas.addPaintListener(new PaintListener()
  {
   @Override
   public void paintControl(PaintEvent e)
   {
    GC gc = e.gc;
    drawGraphcis(display, gc);
   }

  });
  gc.dispose();

 }

 public static void main(String[] args)
 {

  /* Instantiate Display object, it represents SWT session */
  Display display = new Display();

  /*
   * Define Shell, it represent a window, You can add more than one shell to Display
   */
  Shell shell = new Shell(display);
  shell.setSize(shellWidth, shellHeight);
  shell.setText("SWT Tutorial");

  addGraphicsToShell(display, shell);

  /*
   * Run the event dispatching loop until an exit condition occurs, which is typically when the main shell window
   * is closed by the user.
   */

  while (!shell.isDisposed()) {
   if (!display.readAndDispatch()) {
    display.sleep();
   }
  }

  /* Dispose the display */
  display.dispose();

 }
}

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