Java Tutorial/SWT/Canvas

Add Controls to Canvas

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class CanvasControlAdd {
  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    shell.setText("Canvas Example");
    shell.setLayout(new FillLayout());
    Canvas canvas = new Canvas(shell, SWT.NONE);
    Button button = new Button(canvas, SWT.PUSH);
    button.setBounds(10, 10, 300, 40);
    button.setText("You can place widgets on a canvas");
    canvas.addPaintListener(new PaintListener() {
      public void paintControl(PaintEvent e) {
        Rectangle rect = ((Canvas) e.widget).getBounds();
        e.gc.setForeground(e.display.getSystemColor(SWT.COLOR_RED));
        e.gc.drawFocus(5, 5, rect.width - 10, rect.height - 10);
        e.gc.drawText("You can draw text directly on a canvas", 60, 60);
      }
    });
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
    display.dispose();
  }
}

Add KeyEvent to Canvas

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.KeyEvent;
import org.eclipse.swt.events.KeyListener;
import org.eclipse.swt.graphics.Font;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.RowLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class CanvasKeyEvent {
  public static void main(String[] args) {
    final Display display = new Display();
    Shell shell = new Shell(display);
    
    shell.setLayout(new RowLayout());
    final Canvas canvas = new Canvas(shell, SWT.NULL);
    canvas.setSize(500, 500);
    canvas.setBackground(display.getSystemColor(SWT.COLOR_YELLOW));
    canvas.addKeyListener(new KeyListener() {
      public void keyPressed(KeyEvent e) {
        GC gc = new GC(canvas);
        Rectangle rect = canvas.getClientArea();
        gc.fillRectangle(rect.x, rect.y, rect.width, rect.height);
        
        Font font = new Font(display, "Arial", 32, SWT.BOLD );
        gc.setFont(font);
        
        gc.drawString("" + e.character, 15, 10);
        
        gc.dispose();
        font.dispose();
      }
      public void keyReleased(KeyEvent e) {
      }
    });
    
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
  }
}

Add Traverse event to Canvas

import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;
public class CanvasTranverseEvent {
  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    
    final Canvas c = new Canvas(shell, SWT.BORDER);
    c.setBounds(10, 50, 100, 32);
    c.addListener(SWT.Traverse, new Listener() {
      public void handleEvent(Event e) {
        switch (e.detail) {
        /* Do tab group traversal */
        case SWT.TRAVERSE_ESCAPE:
          System.out.println("SWT.TRAVERSE_ESCAPE");
          break;
        case SWT.TRAVERSE_RETURN:
        case SWT.TRAVERSE_TAB_NEXT:
          System.out.println("SWT.TRAVERSE_TAB_NEXT");
          break;
        case SWT.TRAVERSE_TAB_PREVIOUS:
        case SWT.TRAVERSE_PAGE_NEXT:
        case SWT.TRAVERSE_PAGE_PREVIOUS:
          e.doit = true;
          break;
        }
      }
    });
    Text t = new Text(shell, SWT.SINGLE | SWT.BORDER);
    t.setBounds(10, 85, 100, 32);
    c.setFocus();
    shell.setSize(200, 200);
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch())
        display.sleep();
    }
    display.dispose();
  }
}

Canvas: scroll an image (flicker free, no double buffering)

/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
/*
 * Canvas example snippet: scroll an image (flicker free, no double buffering)
 *
 * For a list of all SWT example snippets see
 * http://www.eclipse.org/swt/snippets/
 */
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.FileDialog;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.ScrollBar;
import org.eclipse.swt.widgets.Shell;
public class ImageScrollFlickerFree {
  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    shell.setLayout(new FillLayout());
    Image originalImage = null;
    FileDialog dialog = new FileDialog(shell, SWT.OPEN);
    dialog.setText("Open an image file or cancel");
    String string = dialog.open();
    if (string != null) {
      originalImage = new Image(display, string);
    }
    if (originalImage == null) {
      int width = 150, height = 200;
      originalImage = new Image(display, width, height);
      GC gc = new GC(originalImage);
      gc.fillRectangle(0, 0, width, height);
      gc.drawLine(0, 0, width, height);
      gc.drawLine(0, height, width, 0);
      gc.drawText("Default Image", 10, 10);
      gc.dispose();
    }
    final Image image = originalImage;
    final Point origin = new Point(0, 0);
    final Canvas canvas = new Canvas(shell, SWT.NO_BACKGROUND | SWT.NO_REDRAW_RESIZE | SWT.V_SCROLL
        | SWT.H_SCROLL);
    final ScrollBar hBar = canvas.getHorizontalBar();
    hBar.addListener(SWT.Selection, new Listener() {
      public void handleEvent(Event e) {
        int hSelection = hBar.getSelection();
        int destX = -hSelection - origin.x;
        Rectangle rect = image.getBounds();
        canvas.scroll(destX, 0, 0, 0, rect.width, rect.height, false);
        origin.x = -hSelection;
      }
    });
    final ScrollBar vBar = canvas.getVerticalBar();
    vBar.addListener(SWT.Selection, new Listener() {
      public void handleEvent(Event e) {
        int vSelection = vBar.getSelection();
        int destY = -vSelection - origin.y;
        Rectangle rect = image.getBounds();
        canvas.scroll(0, destY, 0, 0, rect.width, rect.height, false);
        origin.y = -vSelection;
      }
    });
    canvas.addListener(SWT.Resize, new Listener() {
      public void handleEvent(Event e) {
        Rectangle rect = image.getBounds();
        Rectangle client = canvas.getClientArea();
        hBar.setMaximum(rect.width);
        vBar.setMaximum(rect.height);
        hBar.setThumb(Math.min(rect.width, client.width));
        vBar.setThumb(Math.min(rect.height, client.height));
        int hPage = rect.width - client.width;
        int vPage = rect.height - client.height;
        int hSelection = hBar.getSelection();
        int vSelection = vBar.getSelection();
        if (hSelection >= hPage) {
          if (hPage <= 0)
            hSelection = 0;
          origin.x = -hSelection;
        }
        if (vSelection >= vPage) {
          if (vPage <= 0)
            vSelection = 0;
          origin.y = -vSelection;
        }
        canvas.redraw();
      }
    });
    canvas.addListener(SWT.Paint, new Listener() {
      public void handleEvent(Event e) {
        GC gc = e.gc;
        gc.drawImage(image, origin.x, origin.y);
        Rectangle rect = image.getBounds();
        Rectangle client = canvas.getClientArea();
        int marginWidth = client.width - rect.width;
        if (marginWidth > 0) {
          gc.fillRectangle(rect.width, 0, marginWidth, client.height);
        }
        int marginHeight = client.height - rect.height;
        if (marginHeight > 0) {
          gc.fillRectangle(0, rect.height, client.width, marginHeight);
        }
      }
    });
    shell.setSize(200, 150);
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch())
        display.sleep();
    }
    originalImage.dispose();
    display.dispose();
  }
}

Repaint Canvas

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class CanvasRepaint {
  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    shell.setText("Canvas Example");
    shell.setLayout(new FillLayout());
    Canvas canvas = new Canvas(shell, SWT.NONE);
    canvas.addPaintListener(new PaintListener() {
      public void paintControl(PaintEvent e) {
        e.gc.drawRoundRectangle(10, 10, 200, 200, 30, 30);
      }
    });
    
    canvas.redraw();
    
    
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
    display.dispose();
  }
}