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scrolling an image in a canvas [message #504523]

Mon, 21 December 2009 09:07

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

Hi,
I'm trying to paint an image into a canvas with scrolling support, but the following code is not working:

   public void createPartControl(Composite parent) {
		
	// now create a canvas for this view
	this.canvas = new Canvas( parent, SWT.H_SCROLL | SWT.V_SCROLL );
	// this canvas must show the image when loaded
	this.canvas.addPaintListener( new PaintListener(){

	    @Override
	    public void paintControl(PaintEvent event) {
		// the system wants to show the canvas, so draw the image
		GC graphicContext = event.gc;
		if( image != null )
		    graphicContext.drawImage( image, 0, 0 );		
	    }
	    
	});

I've also tried to use a scrolled composite, but it does not even paint the image:

   public void createPartControl(Composite parent) {
		
        ScrolledComposite scolled = new ScrolledComposite(parent, SWT.H_SCROLL | SWT.V_SCROLL);
	// now create a canvas for this view
	this.canvas = new Canvas( scrolled, SWT.NONE );
	// this canvas must show the image when loaded
	this.canvas.addPaintListener( new PaintListener(){

	    @Override
	    public void paintControl(PaintEvent event) {
		// the system wants to show the canvas, so draw the image
		GC graphicContext = event.gc;
		if( image != null )
		    graphicContext.drawImage( image, 0, 0 );		
	    }
	    
	});

Anyone can help me on how to get the image supporting scrolling?

Thanks

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Re: scrolling an image in a canvas [message #504566 is a reply to message #504523]

Mon, 21 December 2009 14:32

Grant Gayed

Messages: 2150
Registered: July 2009

Senior Member

see
http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.swt.sni ppets/src/org/eclipse/swt/snippets/Snippet48.java?view=co

"Luca Ferrari" <fluca1978@infinito.it> wrote in message
news:hgndru$h0v$1@build.eclipse.org...
> Hi,
> I'm trying to paint an image into a canvas with scrolling support, but the
following code is not working:
>
>
> public void createPartControl(Composite parent) {
>
> // now create a canvas for this view
> this.canvas = new Canvas( parent, SWT.H_SCROLL | SWT.V_SCROLL );
> // this canvas must show the image when loaded
> this.canvas.addPaintListener( new PaintListener(){
>
> @Override
> public void paintControl(PaintEvent event) {
> // the system wants to show the canvas, so draw the image
> GC graphicContext = event.gc;
> if( image != null )
> graphicContext.drawImage( image, 0, 0 );
> }
>
> });
>
>
> I've also tried to use a scrolled composite, but it does not even paint
the image:
>
>
> public void createPartControl(Composite parent) {
>
> ScrolledComposite scolled = new ScrolledComposite(parent,
SWT.H_SCROLL | SWT.V_SCROLL);
> // now create a canvas for this view
> this.canvas = new Canvas( scrolled, SWT.NONE );
> // this canvas must show the image when loaded
> this.canvas.addPaintListener( new PaintListener(){
>
> @Override
> public void paintControl(PaintEvent event) {
> // the system wants to show the canvas, so draw the image
> GC graphicContext = event.gc;
> if( image != null )
> graphicContext.drawImage( image, 0, 0 );
> }
>
> });
>
>
> Anyone can help me on how to get the image supporting scrolling?
>
> Thanks

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Re: scrolling an image in a canvas [message #504710 is a reply to message #504566]

Tue, 22 December 2009 05:01

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

Thanks,
I did that and of course ti works, but is a quite lot of work for a simple functionality like scrolling a composite content. Is there anything simpler to use in SWT? Something that can offer the JScrollPane of swing features?

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Re: scrolling an image in a canvas [message #504713 is a reply to message #504710]

Tue, 22 December 2009 10:17

Dmitry K

Messages: 17
Registered: July 2009

Junior Member

Maybe
http://www.eclipse.org/articles/Article-Image-Viewer/Image_v iewer.html

Should be helpful?

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Re: scrolling an image in a canvas [message #504793 is a reply to message #504713]

Tue, 22 December 2009 17:22

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

Yes thanks, it is very helpful.
However it still empathizes how SWT is lacking (?) an equivalent component like JScrollPane. Is there a particular reason for that? Why ScolledComposite cannot just embed an image and provide the scrolling capabilities? I'm really curious to understand.

Thanks

P.S.
in the meantime I've succeeded implementing an image-view following your suggestions.

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Re: scrolling an image in a canvas [message #504819 is a reply to message #504793]

Tue, 22 December 2009 19:36

Lakshmi P Shanmugam

Messages: 279
Registered: July 2009
Location: India

Senior Member

The ScrolledComposite provides the scrolling capabilities and can be used to scroll the image. In your example, you have to also set the bounds of the canvas for the image to be visible.
--> this.canvas.setBounds(image.getBounds());

Please see --
http://dev.eclipse.org/viewcvs/index.cgi/org.eclipse.swt.sni ppets/src/org/eclipse/swt/snippets/Snippet215.java?view=co

Lakshmi P Shanmugam

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Re: scrolling an image in a canvas [message #504872 is a reply to message #504819]

Wed, 23 December 2009 04:26

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

Uhm...this is not working for me:

  public void createPartControl(Composite parent) {
		
	// create a scrolling composite
	ScrolledComposite scroller = new ScrolledComposite(parent, SWT.V_SCROLL | SWT.H_SCROLL );
	
	// now create a canvas for this view
	this.canvas = new Canvas( scroller, SWT.NONE );
	scroller.setContent(scroller);
	
	// this canvas must show the image when loaded
	this.canvas.addPaintListener( new PaintListener(){

	    @Override
	    public void paintControl(PaintEvent event) {
		// the system wants to show the canvas, so draw the image
		GC graphicContext = event.gc;
		if( image != null ){
		    // draw the image at the current image position
		    graphicContext.drawImage( image, imageLeftCornerPosition.x, imageLeftCornerPosition.y );
		    canvas.setBounds( image.getBounds() );
		}
	    }
	    
	});

in fact I cannot see any scroll bar on the view. I cannot set the canvas bounds before the image is painted, could it be that the problem?

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Re: scrolling an image in a canvas [message #504898 is a reply to message #504793]

Wed, 23 December 2009 12:33

Lakshmi P Shanmugam

Messages: 279
Registered: July 2009
Location: India

Senior Member

When the bounds of the canvas is zero, canvas doesn't have any visible area to be painted. So, it doesn't get the Paint event and the PaintListener is not called.

You can set the bounds of the canvas to a non-zero value outside the PaintListener so that it can receive the Paint events. You can reset it to the bounds of the image in the PaintListener.

ScrolledComposite scroller = new ScrolledComposite(parent, SWT.V_SCROLL | SWT.H_SCROLL );
final Canvas canvas = new Canvas( scroller, SWT.NONE );
scroller.setContent(scroller);
canvas.setBounds(display.getBounds());
canvas.addPaintListener( new PaintListener(){
public void paintControl(PaintEvent event) {
event.gc.drawImage(image, 0, 0);
canvas.setBounds(image.getBounds());
}
});

Lakshmi P Shanmugam

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Re: scrolling an image in a canvas [message #505156 is a reply to message #504898]

Mon, 28 December 2009 08:04

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

No way to obtain the scrolling:

  public void createPartControl(Composite parent) {
		
	// create a scrolling composite
	ScrolledComposite scroller = new ScrolledComposite(parent, SWT.V_SCROLL | SWT.H_SCROLL );
	
	// now create a canvas for this view
	this.canvas = new Canvas( scroller, SWT.NONE );
	scroller.setContent(scroller);
	this.canvas.setBounds( this.getSite().getShell().getDisplay().getBounds() );
	
	// this canvas must show the image when loaded
	this.canvas.addPaintListener( new PaintListener(){

	    @Override
	    public void paintControl(PaintEvent event) {
		// the system wants to show the canvas, so draw the image
		GC graphicContext = event.gc;
		if( image != null ){
		    // draw the image at the current image position
		    graphicContext.drawImage( image, imageLeftCornerPosition.x, imageLeftCornerPosition.y );
		    canvas.setBounds( image.getBounds() );
		}
	    }
	    
	});

I cannot see the scrolling bars even if I resize the view. I cannot understand why scrolling bars are not even shown. Any help?

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Re: scrolling an image in a canvas [message #506874 is a reply to message #505156]

Mon, 11 January 2010 09:00

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

I've made a simple change but it still does not work:

public void createPartControl(Composite parent) {
		
	// create a scrolling composite
	ScrolledComposite scroller = new ScrolledComposite(parent, SWT.V_SCROLL | SWT.H_SCROLL );
	
	// now create a canvas for this view
	this.canvas = new Canvas( scroller, SWT.NONE );
	this.canvas.setBounds( this.getSite().getShell().getDisplay().getBounds() );
[B]	scroller.setContent( this.canvas );[/B]
	
	
	// this canvas must show the image when loaded
	this.canvas.addPaintListener( new PaintListener(){

	    @Override
	    public void paintControl(PaintEvent event) {
		// the system wants to show the canvas, so draw the image
		GC graphicContext = event.gc;
		if( image != null ){
		    // draw the image at the current image position
		    graphicContext.drawImage( image, imageLeftCornerPosition.x, imageLeftCornerPosition.y );
		    canvas.setBounds( image.getBounds() );
		}
	    }
	    
	});

Now I've got a suspect: the paint listener draws the image at the

imageLeftCornerPosition.x, imageLeftCornerPosition.y

that are set both to zero. So this means that even if the scrollbar moves the image is always displayed at (0,0). Now my doubt is that the problem is with the pain listener, that forces the image to be shown in the canvas at the same position. Should I remove it? And if I remove how can I display the image when it is loaded?

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Re: scrolling an image in a canvas [message #508854 is a reply to message #506874]

Wed, 20 January 2010 14:57

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

I've found that if I remove the paint listener, and therefore I remove the painting at corner 0,0 the scroller seems to work:

 public void createPartControl(Composite parent) {
		
	// create a scrolling composite
	ScrolledComposite scroller = new ScrolledComposite(parent, SWT.V_SCROLL | SWT.H_SCROLL );
	
	// now create a canvas for this view
	this.canvas = new Canvas( scroller, SWT.NONE );
	this.canvas.setBounds( this.getSite().getShell().getDisplay().getBounds() );
	scroller.setContent( this.canvas );
	
	
	// this canvas must show the image when loaded
	this.canvas.addPaintListener( new PaintListener(){

	    boolean paint = true; 
	    @Override
	    public void paintControl(PaintEvent event) {
		// the system wants to show the canvas, so draw the image
		GC graphicContext = event.gc;
		if( image != null && paint ){
		    // draw the image at the current image position
		    graphicContext.drawImage( image, 0, 0 );
		    canvas.setBounds( image.getBounds() );
		    paint = false;
		}
	    }
	    
	});

The problem now is that the image scrolls, but cannot be repaint. For instance, if I scroll to right, the image moves, but when I scroll back to left, the image is not shown and so I got the background color. Any suggestion?

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Re: scrolling an image in a canvas [message #508887 is a reply to message #508854]

Wed, 20 January 2010 16:08

Luca Ferrari

Messages: 159
Registered: November 2009

Senior Member

At last I got it, it seems that the canvas.setBounds inside the paint listener was disturbing the image repainting thru the scrolled composite. The final code working is the following:

 public void createPartControl(Composite parent) {
		
	// create a scrolling composite
	ScrolledComposite scroller = new ScrolledComposite(parent, SWT.V_SCROLL | SWT.H_SCROLL );
	
	// now create a canvas for this view
	this.canvas = new Canvas( scroller, SWT.NONE );
	scroller.setContent( this.canvas );
	
	
	// this canvas must show the image when loaded
	
	this.canvas.addPaintListener( new PaintListener(){

 
	    @Override
	    public void paintControl(PaintEvent event) {
		if( image != null )
		    event.gc.drawImage(image, 0, 0 );
	    }
	    
	});

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