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/*******************************************************************************
* Copyright (c) 2000, 2011 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
*******************************************************************************/
package org.eclipse.compare.internal;
import org.eclipse.swt.*;
import org.eclipse.swt.widgets.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.events.*;
/**
* A Canvas which reduces flicker by drawing in an off screen buffer.
*/
public abstract class BufferedCanvas extends Canvas {
//private static final boolean USE_DOUBLE_BUFFER= !"carbon".equals(SWT.getPlatform()); //$NON-NLS-1$
private static final boolean USE_DOUBLE_BUFFER= true;
/** The drawable for double buffering */
Image fBuffer;
public BufferedCanvas(Composite parent, int flags) {
super(parent, flags | SWT.NO_BACKGROUND);
addPaintListener(
new PaintListener() {
@Override
public void paintControl(PaintEvent event) {
doubleBufferPaint(event.gc);
}
}
);
addDisposeListener(
new DisposeListener() {
@Override
public void widgetDisposed(DisposeEvent e) {
if (fBuffer != null) {
fBuffer.dispose();
fBuffer= null;
}
}
}
);
}
public void repaint() {
if (!isDisposed()) {
GC gc= new GC(this);
doubleBufferPaint(gc);
gc.dispose();
}
}
/*
* Double buffer drawing.
*/
void doubleBufferPaint(GC dest) {
if (!USE_DOUBLE_BUFFER) {
doPaint(dest);
return;
}
Point size= getSize();
if (size.x <= 1 || size.y <= 1) // we test for <= 1 because on X11 controls have initial size 1,1
return;
if (fBuffer != null) {
Rectangle r= fBuffer.getBounds();
if (r.width != size.x || r.height != size.y) {
fBuffer.dispose();
fBuffer= null;
}
}
if (fBuffer == null)
fBuffer= new Image(getDisplay(), size.x, size.y);
GC gc= new GC(fBuffer);
try {
gc.setBackground(getBackground());
gc.fillRectangle(0, 0, size.x, size.y);
doPaint(gc);
} finally {
gc.dispose();
}
dest.drawImage(fBuffer, 0, 0);
}
abstract public void doPaint(GC gc);
}
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