alecail alecail - 1 year ago 124
Objective-C Question

How to have CATextLayer smooth its text?

According to the documentation, it is possible to enable font smoothing inside CATextLayer:

Text can only be drawn using sub-pixel antialiasing when it is composited into an existing opaque background at the same time that it's rasterized.

Here is how I understand this sentence:

@implementation CATextLayerWithFontSmoothing
-(id)init {
self=[super init];
if (self) {
CALayer * whiteBackground = [CALayer layer];
CATextLayer * blackText = [CATextLayer layer];

[whiteBackground setBounds:NSMakeRect(0, 0, 300, 300)];
[blackText setBounds:NSMakeRect(0, 0, 300, 300)];

[whiteBackground setBackgroundColor:[NSColor whiteColor].CGColor];
[blackText setForegroundColor:[NSColor blackColor].CGColor];
[blackText setString:@"CATextLayer"];

[blackText setShouldRasterize:YES];

[self addSublayer:whiteBackground];
[self addSublayer: blackText];

return self;

which doesn't work. Text is not drawn using subpixel anti-aliasing.

Answer Source

The method described here works:

Case 2: If you're using a CATextLayer directly, you'll need to subclass CATextLayer and do something like the following in your drawing code:

- (void)drawInContext:(CGContextRef)ctx
CGContextSetRGBFillColor (ctx, r, g, b, a);
CGContextFillRect (ctx, [self bounds]);
CGContextSetShouldSmoothFonts (ctx, true);
[super drawInContext:ctx];

Here is a comparison of smoothed vs non-smoothed:

text on a regular CATextLayer

text with sub-pixel-aa

800% zoom of both layers

PS: Don't look at this answer on a CRT.