#414: slow StyledTextRenderer for unicode and unprintable control cha…

…racters

This test replaces the characters 0x00-0x1F with some alternative
character (by default '?') for rendering. This improves the performance
significantly.

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/TextLayout.java

@@ -2854,6 +2854,13 @@ public boolean isDisposed () {
 	return device == null;
 }
 
+private static char replaceBelowSpaceCharacters(char chr) {
+	return chr >= ' '
+		? chr
+		//: (char)(0x2400 + chr);
+		: '?';
+}
+
 /*
  *  Itemize the receiver text
  */
@@ -2881,6 +2888,9 @@ StyleItem[] itemize () {
 	int[] pcItems = new int[1];
 	char[] chars = new char[length];
 	segmentsText.getChars(0, length, chars, 0);
+	for (int i = 0; i < length; i++) {
+		chars[i] = replaceBelowSpaceCharacters(chars[i]);
+	}
 	// enable font ligatures
 	scriptControl.fMergeNeutralItems = true;
 	/*
@@ -3740,6 +3750,9 @@ void shape (GC  gc, final long hdc, final StyleItem run) {
 	final int[] buffer = new int[1];
 	final char[] chars = new char[run.length];
 	segmentsText.getChars(run.start, run.start + run.length, chars, 0);
+	for (int i = 0; i < chars.length; i++) {
+		chars[i] = replaceBelowSpaceCharacters(chars[i]);
+	}
 
 	final int maxGlyphs = (chars.length * 3 / 2) + 16;
 	long hHeap = OS.GetProcessHeap();