Drawing animated focus rings in Cocoa

example.m

#import <dlfcn.h>

static off_t lookupPrivateSymbol(const char *path, const char *symbol)
{
    // TODO: Parse the Mach-O file
    NSTask *task = [[NSTask alloc] init];
    task.launchPath = @"/usr/bin/nm";
    task.arguments = @[@"-a", @(path)];
    NSPipe *outputPipe = [NSPipe pipe];
    task.standardOutput = outputPipe;
    [task launch];
    NSData *data = [[outputPipe fileHandleForReading] readDataToEndOfFile];
    [task waitUntilExit];

    NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSArray<NSString *> *lines = [string componentsSeparatedByString:@"\n"];
    for (NSString *line in lines) {
        if ([line containsString:@(symbol)]) {
            NSScanner *scanner = [NSScanner scannerWithString:[[line componentsSeparatedByString:@" "] firstObject]];
            unsigned long long offset = 0;
            [scanner scanHexLongLong:&offset];
            return (off_t)offset;
        }
    }

    return 0;
}

static void qt_drawFocusRingOnPath(CGContextRef cg, NSBezierPath *focusRingPath, NSTimeInterval time)
{
    CGContextSaveGState(cg);
    CGContextBeginTransparencyLayer(cg, NULL);
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:[NSGraphicsContext
                                          graphicsContextWithGraphicsPort:(CGContextRef)cg flipped:NO]];

    NSNumber *useAnimatedFocusRing = [[NSUserDefaults standardUserDefaults] objectForKey:@"NSUseAnimatedFocusRing"];
    if (![useAnimatedFocusRing isKindOfClass:[NSNumber class]])
        useAnimatedFocusRing = nil;

    BOOL hasYosemite = YES; // TODO: >= 10.10

    // rdar://23700589
    typedef void (*_NSSetFocusRingStyleForTimeFunction)(NSFocusRingPlacement placement, NSTimeInterval time);
    static _NSSetFocusRingStyleForTimeFunction _NSSetFocusRingStyleForTime = 0;
    if (!_NSSetFocusRingStyleForTime && hasYosemite) {
        Dl_info info;
        dladdr(&NSAppKitVersionNumber, &info);
        off_t addr = lookupPrivateSymbol(info.dli_fname, "_NSSetFocusRingStyleForTime");
        if (addr)
            _NSSetFocusRingStyleForTime = (_NSSetFocusRingStyleForTimeFunction)(info.dli_fbase + addr);
    }

    if (_NSSetFocusRingStyleForTime && (!useAnimatedFocusRing || [useAnimatedFocusRing boolValue]))
        _NSSetFocusRingStyleForTime(NSFocusRingOnly, time); // 0 <= time <= 0.25
    else
        NSSetFocusRingStyle(NSFocusRingOnly);

    [focusRingPath setClip]; // Clear clip path to avoid artifacts when rendering the cursor at zero pos
    [focusRingPath fill];
    [NSGraphicsContext restoreGraphicsState];
    CGContextEndTransparencyLayer(cg);
    CGContextRestoreGState(cg);
}