BufferedCanvas.java

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package edu.rice.cs.hpc.traceviewer.painter;

import org.eclipse.jface.action.Action;
import org.eclipse.jface.action.MenuManager;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.DisposeEvent;
import org.eclipse.swt.events.DisposeListener;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.ImageData;
import org.eclipse.swt.graphics.ImageLoader;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.FileDialog;
import org.eclipse.swt.widgets.Menu;


/*************************************************************************
 * 
 * Standard abstract canvas that contains a buffered image and 
 *  context menu to save the buffered image to a file
 *
 *************************************************************************/
public abstract class BufferedCanvas extends Canvas 
    implements PaintListener, DisposeListener
{
    
    /*** buffer image for displaying the canvas ****/
    protected Image imageBuffer;

    public BufferedCanvas(Composite parent) 
    {
        super(parent, SWT.NO_BACKGROUND);
        addPaintListener(this);
        addDisposeListener(this);
        
        setContextMenus();
    }

    @Override
    /*
     * (non-Javadoc)
     * @see org.eclipse.swt.events.PaintListener#paintControl(org.eclipse.swt.events.PaintEvent)
     */
    public void paintControl(PaintEvent e) 
    {
        if (imageBuffer != null) 
        {
            final Rectangle area = getClientArea();
            final Rectangle rect = imageBuffer.getBounds();
            
            try {
                // Stretch or shrink the image automatically
                e.gc.drawImage(imageBuffer, 0, 0, rect.width, rect.height, 
                        0, 0, area.width, area.height);
            }
            catch (Exception ex)
            {
                // An exception "Illegal argument" will be raised if the resize method is not "fast" enough to create the image
                //      buffer before the painting is called. Thus, it causes inconsistency between the size of the image buffer
                //      and the size of client area. 
                //      If this happens, either we wait for the creation of image buffer, or do nothing. 
                //      I prefer to do nothing because of scalability concerns.
                return;
            }
        }
    }
    
    /******
     * initialization when a new data arrives
     */
    protected void initBuffer() 
    {
        if (imageBuffer != null && !imageBuffer.isDisposed())  
        {
            imageBuffer.dispose();
        }
        imageBuffer = null;
    }
    
    protected void setBuffer(Image buffer)
    {
        this.imageBuffer = buffer;
    }
    
    protected Image getBuffer()
    {
        return imageBuffer;
    }
    

    @Override
    /*
     * (non-Javadoc)
     * @see org.eclipse.swt.events.DisposeListener#widgetDisposed(org.eclipse.swt.events.DisposeEvent)
     */
    public void widgetDisposed(DisposeEvent e)
    {
        if (imageBuffer != null)
            imageBuffer.dispose();
    }
    
    /*************************************************************************
     * add context menus for the canvas
     *************************************************************************/
    private void setContextMenus() {
        
        final Action saveImage = new Action("Save image ...") {
            
            public void run() {
                
                if (imageBuffer == null)
                    return;
                
                FileDialog dialog = new FileDialog(getShell(), SWT.SAVE);
                dialog.setText("Save image ... ");
                dialog.setFilterExtensions(new String[] {"*.png"});
                String filename = dialog.open();
                if (filename == null) {
                    return;
                }
                
                // get image data from the buffer
                ImageData data = BufferedCanvas.this.imageBuffer.getImageData();
                ImageLoader loader = new ImageLoader();
                loader.data = new ImageData[] {data};
                
                // save the data into a file with PNG format
                loader.save(filename, SWT.IMAGE_PNG);
            }
        };
        
        // add menus to the canvas
        MenuManager mnuMgr = new MenuManager();
        Menu menu = mnuMgr.createContextMenu(this);
        mnuMgr.add(saveImage);

        setMenu(menu);
    }
}