Display hidden characters in NSTextView - cocoa

Question

I am writing a text editor for Mac OS X. I need to display hidden characters in an NSTextView (such as spaces, tabs, and special characters). I have spent a lot of time searching for how to do this but so far I have not found an answer. If anyone could point me in the right direction I would be grateful.

Answer 1

Here's a fully working and clean implementation
#interface GILayoutManager : NSLayoutManager
#end
#implementation GILayoutManager
- (void)drawGlyphsForGlyphRange:(NSRange)range atPoint:(NSPoint)point {
NSTextStorage* storage = self.textStorage;
NSString* string = storage.string;
for (NSUInteger glyphIndex = range.location; glyphIndex < range.location + range.length; glyphIndex++) {
NSUInteger characterIndex = [self characterIndexForGlyphAtIndex: glyphIndex];
switch ([string characterAtIndex:characterIndex]) {
case ' ': {
NSFont* font = [storage attribute:NSFontAttributeName atIndex:characterIndex effectiveRange:NULL];
[self replaceGlyphAtIndex:glyphIndex withGlyph:[font glyphWithName:#"periodcentered"]];
break;
}
case '\n': {
NSFont* font = [storage attribute:NSFontAttributeName atIndex:characterIndex effectiveRange:NULL];
[self replaceGlyphAtIndex:glyphIndex withGlyph:[font glyphWithName:#"carriagereturn"]];
break;
}
}
}
[super drawGlyphsForGlyphRange:range atPoint:point];
}
#end
To install, use:
[myTextView.textContainer replaceLayoutManager:[[GILayoutManager alloc] init]];
To find font glyph names, you have to go to CoreGraphics:
CGFontRef font = CGFontCreateWithFontName(CFSTR("Menlo-Regular"));
for (size_t i = 0; i < CGFontGetNumberOfGlyphs(font); ++i) {
printf("%s\n", [CFBridgingRelease(CGFontCopyGlyphNameForGlyph(font, i)) UTF8String]);
}

Answer 2

Have a look at the NSLayoutManager class. Your NSTextView will have a layout manager associated with it, and the layout manager is responsible for associating a character (space, tab, etc.) with a glyph (the image of that character drawn on the screen).
In your case, you would probably be most interested in the replaceGlyphAtIndex:withGlyph: method, which would allow you to replace individual glyphs.

Answer 3

I wrote a text editor a few years back - here's some meaningless code that should get you looking in (hopefully) the right direction (this is an NSLayoutManager subclass btw - and yes I know it's leaking like the proverbial kitchen sink):
- (void)drawGlyphsForGlyphRange:(NSRange)glyphRange atPoint:(NSPoint)containerOrigin
{
if ([[[[MJDocumentController sharedDocumentController] currentDocument] editor] showInvisibles])
{
//init glyphs
unichar crlf = 0x00B6;
NSString *CRLF = [[NSString alloc] initWithCharacters:&crlf length:1];
unichar space = 0x00B7;
NSString *SPACE = [[NSString alloc] initWithCharacters:&space length:1];
unichar tab = 0x2192;
NSString *TAB = [[NSString alloc] initWithCharacters:&tab length:1];
NSString *docContents = [[self textStorage] string];
NSString *glyph;
NSPoint glyphPoint;
NSRect glyphRect;
NSDictionary *attr = [[NSDictionary alloc] initWithObjectsAndKeys:[NSUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:#"invisiblesColor"]], NSForegroundColorAttributeName, nil];
//loop thru current range, drawing glyphs
int i;
for (i = glyphRange.location; i < NSMaxRange(glyphRange); i++)
{
glyph = #"";
//look for special chars
switch ([docContents characterAtIndex:i])
{
//space
case ' ':
glyph = SPACE;
break;
//tab
case '\t':
glyph = TAB;
break;
//eol
case 0x2028:
case 0x2029:
case '\n':
case '\r':
glyph = CRLF;
break;
//do nothing
default:
glyph = #"";
break;
}
//should we draw?
if ([glyph length])
{
glyphPoint = [self locationForGlyphAtIndex:i];
glyphRect = [self lineFragmentRectForGlyphAtIndex:i effectiveRange:NULL];
glyphPoint.x += glyphRect.origin.x;
glyphPoint.y = glyphRect.origin.y;
[glyph drawAtPoint:glyphPoint withAttributes:attr];
}
}
}
[super drawGlyphsForGlyphRange:glyphRange atPoint:containerOrigin];
}

Answer 4

I solved the problem of converting between NSGlyphs and the corresponding unichar in the NSTextView. The code below works beautifully and replaces spaces with bullets for visible text:
- (void)drawGlyphsForGlyphRange:(NSRange)range atPoint:(NSPoint)origin
{
NSFont *font = [[CURRENT_TEXT_VIEW typingAttributes]
objectForKey:NSFontAttributeName];
NSGlyph bullet = [font glyphWithName:#"bullet"];
for (int i = range.location; i != range.location + range.length; i++)
{
unsigned charIndex = [self characterIndexForGlyphAtIndex:i];
unichar c =[[[self textStorage] string] characterAtIndex:charIndex];
if (c == ' ')
[self replaceGlyphAtIndex:charIndex withGlyph:bullet];
}
[super drawGlyphsForGlyphRange:range atPoint:origin];
}

Answer 5

Perhaps -[NSLayoutManager setShowsControlCharacters:] and/or -[NSLayoutManager setShowsInvisibleCharacters:] will do what you want.

Answer 6

Here is Pol's solution in Swift:
class MyLayoutManager: NSLayoutManager {
override func drawGlyphsForGlyphRange(glyphsToShow: NSRange, atPoint origin: NSPoint) {
if let storage = self.textStorage {
let s = storage.string
let startIndex = s.startIndex
for var glyphIndex = glyphsToShow.location; glyphIndex < glyphsToShow.location + glyphsToShow.length; glyphIndex++ {
let characterIndex = self.characterIndexForGlyphAtIndex(glyphIndex)
let ch = s[startIndex.advancedBy(characterIndex)]
switch ch {
case " ":
let attrs = storage.attributesAtIndex(characterIndex, effectiveRange: nil)
if let font = attrs[NSFontAttributeName] {
let g = font.glyphWithName("periodcentered")
self.replaceGlyphAtIndex(glyphIndex, withGlyph: g)
}
case "\n":
let attrs = storage.attributesAtIndex(characterIndex, effectiveRange: nil)
if let font = attrs[NSFontAttributeName] {
// let g = font.glyphWithName("carriagereturn")
let g = font.glyphWithName("paragraph")
self.replaceGlyphAtIndex(glyphIndex, withGlyph: g)
}
case "\t":
let attrs = storage.attributesAtIndex(characterIndex, effectiveRange: nil)
if let font = attrs[NSFontAttributeName] {
let g = font.glyphWithName("arrowdblright")
self.replaceGlyphAtIndex(glyphIndex, withGlyph: g)
}
default:
break
}
}
}
super.drawGlyphsForGlyphRange(glyphsToShow, atPoint: origin)
}
}
And to list the glyph names:
func listFonts() {
let font = CGFontCreateWithFontName("Menlo-Regular")
for var i:UInt16 = 0; i < UInt16(CGFontGetNumberOfGlyphs(font)); i++ {
if let name = CGFontCopyGlyphNameForGlyph(font, i) {
print("name: \(name) at index \(i)")
}
}
}