CALayer shadowPath done the right way

gistfile1.txt

/* 
Source: Apple Developer - Understanding iOS View Compositing
*/

// setup the layer
CALayer *layer = view.layer;
layer.bounds = sublayer_bounds;
layer.backgroundColor = random_color();

// set the shadow properties on the layer
layer.shadowOpacity = 0.5;
layer.shadowRadius = 10;
layer.shadowOffset = CGSizeMake(0, 10);

// get a UIBezierPath (for its CGPath gut)
CGPathRef shadowPath = [UIBezierPath bezierPathWithRect:sublayer_bounds].CGPath;
sublayer.shadowPath = shadowPath;

// set the CGPath as the shadow layer
UIImage *image = [self loadImage];
UIColor *color = [UIColor colorWithWhite:0 alpha:0.5];

// Draw it into context (you always want to draw it into context, all in one rendering pass)
CGContextSetShadowWithColor(ctx, CGSizeMake(0,10) /* offset */, 10 /* blur radius */, color.CGColor);
CGContextDrawImage(ctx, r, image.CGImage);

Can you clarify what ctx is?

the CGContext you are drawing into. CGContextRef context = UIGraphicsGetCurrentContext();

What's the "r" in the CGContextDrawImage