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/*******************************************************************************
* Copyright (c) 2006, 2013 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
* Daesung Ha <nberserk@gmail.com> - supports top and bottom scrolling - https://bugs.eclipse.org/bugs/show_bug.cgi?id=412267
*******************************************************************************/
package org.eclipse.ui.texteditor;
import java.util.ResourceBundle;
import org.eclipse.swt.custom.StyledText;
import org.eclipse.jface.text.source.ISourceViewer;
/**
* An action to handle emacs-like recenter.
* This function scrolls the selected window to put the cursor at the middle/top/bottom of the screen.
*
* @since 3.3
*/
public class RecenterAction extends TextEditorAction {
private static final int RECENTER_MIDDLE= 0;
private static final int RECENTER_TOP= 1;
private static final int RECENTER_BOTTOM= 2;
private static final int RECENTER_POS_SIZE= 3;
private int fPrevOffset= -1;
private int fDestPos;
/**
* Creates a new action for the given text editor. The action configures its
* visual representation from the given resource bundle.
*
* @param bundle the resource bundle
* @param prefix a prefix to be prepended to the various resource keys
* (described in <code>ResourceAction</code> constructor), or
* <code>null</code> if none
* @param editor the text editor
*/
public RecenterAction(ResourceBundle bundle, String prefix, ITextEditor editor) {
super(bundle, prefix, editor);
}
/*
* @see IAction#run()
*/
public void run() {
ITextEditor editor= getTextEditor();
if (!(editor instanceof AbstractTextEditor))
return;
ISourceViewer viewer= ((AbstractTextEditor)editor).getSourceViewer();
if (viewer == null)
return;
StyledText st= viewer.getTextWidget();
if (st == null)
return;
// compute the number of lines displayed
int height= st.getClientArea().height;
int lineHeight= st.getLineHeight();
int rowPerScreen= height / lineHeight;
int caretOffset= st.getCaretOffset();
int caretLine= st.getLineAtOffset(caretOffset);
if (caretOffset==fPrevOffset) { // if successive call in same position
fDestPos++;
fDestPos%= RECENTER_POS_SIZE;
}else{
fDestPos= RECENTER_MIDDLE;
}
fPrevOffset= caretOffset;
int line= 0;
switch (fDestPos) {
case RECENTER_MIDDLE:
line= Math.max(0, (caretLine - rowPerScreen / 2));
break;
case RECENTER_TOP:
line= caretLine;
break;
case RECENTER_BOTTOM:
line= Math.max(0, caretLine - rowPerScreen + 1);
break;
default:
break;
}
st.setTopIndex(line);
}
}
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