fixed behavior of PageUp and PageDown keys, which now always scro…

…ll a whole page up or down

CHANGES.md

@@ -8,6 +8,8 @@ Markdown Writer FX Change Log
 - Project specific options: Select "Store in project" checkbox in Options dialog
   to save options in per project (in file `<project-root>/.markdownwriterfx`).
 - "Format only modified paragraphs on Save" checkbox added to Options dialog.
+- Fixed behavior of `PageUp` and `PageDown` keys, which now always scroll a
+  whole page up or down.
 - Fixed behavior of `Ctrl+RIGHT`, which now moves caret to beginning of next
   word.
 - Disabled "Save As" for read-only editors (binary or too-large files).

src/main/java/org/markdownwriterfx/editor/MarkdownTextArea.java

@@ -113,4 +113,73 @@ public void wordBreaksForwards(int n, SelectionPolicy selectionPolicy) {
 		if (newCaretPosition != caretPosition)
 			moveTo(newCaretPosition, selectionPolicy);
 	}
+
+	@Override
+	public void prevPage(SelectionPolicy selectionPolicy) {
+		disableFollowCaret = true;
+
+		// change behavior of PAGE_UP key:
+		//   old behavior: move caret visible lines count up (scrolling depends on caret position)
+		//   new behavior: scroll one page up and move caret visible lines count up
+		try {
+			int firstVisible = firstVisibleParToAllParIndex();
+			int lastVisible = lastVisibleParToAllParIndex();
+			int caretParagraph = getCurrentParagraph();
+			int caretColumn = getCaretColumn();
+
+			showParagraphAtBottom(firstVisible - 1);
+
+			// TODO improve handling of wrapped lines and tabs
+			int newCaretParagraph = Math.max(firstVisible - (lastVisible - caretParagraph), 0);
+			if (caretParagraph == lastVisible && newCaretParagraph > 0)
+				newCaretParagraph--;
+			int newCaretColumn = Math.min(caretColumn, getParagraphLength(newCaretParagraph));
+			moveTo(newCaretParagraph, newCaretColumn, selectionPolicy);
+		} catch (AssertionError e) {
+			// may be thrown in textArea.visibleParToAllParIndex()
+			// occurs if the last line is empty and and the text fits into
+			// the visible area (no vertical scroll bar shown)
+			// --> ignore
+			super.prevPage(selectionPolicy);
+		}
+	}
+
+	@Override
+	public void nextPage(SelectionPolicy selectionPolicy) {
+		disableFollowCaret = true;
+
+		// change behavior of PAGE_DOWN key:
+		//   old behavior: move caret visible lines count down (scrolling depends on caret position)
+		//   new behavior: scroll one page down and move caret visible lines count down
+		try {
+			int firstVisible = firstVisibleParToAllParIndex();
+			int lastVisible = lastVisibleParToAllParIndex();
+			int caretParagraph = getCurrentParagraph();
+			int caretColumn = getCaretColumn();
+
+			showParagraphAtTop(lastVisible);
+
+			// TODO improve handling of wrapped lines and tabs
+			int newCaretParagraph = Math.min(lastVisible + (caretParagraph - firstVisible), getParagraphs().size() - 1);
+			int newCaretColumn = Math.min(caretColumn, getParagraphLength(newCaretParagraph));
+			moveTo(newCaretParagraph, newCaretColumn, selectionPolicy);
+		} catch (AssertionError e) {
+			// may be thrown in textArea.visibleParToAllParIndex()
+			// occurs if the last line is empty and and the text fits into
+			// the visible area (no vertical scroll bar shown)
+			// --> ignore
+			super.nextPage(selectionPolicy);
+		}
+	}
+
+	private boolean disableFollowCaret;
+
+	@Override
+	public void requestFollowCaret() {
+		if (disableFollowCaret) {
+			disableFollowCaret = false;
+			requestLayout();
+		} else
+			super.requestFollowCaret();
+	}
 }