What do the values in _subtreeDescription output mean?

Question

Calling _subtreeDescription on a custom scroll view shows:

Seohtracker devel[22556:303] [ AF O WLU ] h=-&- v=-&- EHGraph_scroll 0x100c52f20 f=(367,169,250,168) b=(-) => _NSViewBackingLayer(0x101a77500) a={0, 0} p={367, 169} b=(0,0,250,168) superlayer=0x101a756f0 TILED=no TIME drawRect: min/mean/max 0.00/0.00/0.00 ms

p and b seem to be derived from the frame f. What does the parameter a mean?

Nick K9 Nick K9 · Accepted Answer · 2015-10-15T11:21:03

This is a layer, and the names for things are slightly different from views. Having a look at CALayer, what these mean becomes clear pretty quickly.

p = position
b = bounds
a = anchorPoint

Also, if you print the backing layer out directly in LLVM, you get a much more verbose description of the layer's current properties:

(lldb) po 0x6080000c5550
<SCNBackingLayer:0x6080000c5550; position = CGPoint (0 0); bounds = CGRect (0 0; 480 360); delegate = <SCNView: 0x100e03070 | scene=(null) sceneTime=0.000000 frame={{0, 0}, {480, 360}} pointOfView=(null)>; sublayers = (<AVCaptureVideoPreviewLayer: 0x608000026420>, <SCNBackingLayer: 0x6100000c2450>); opaque = YES; masksToBounds = YES; backgroundFilters = (
); filters = (
); shadowColor = (null); anchorPoint = CGPoint (0 0); NS_view = <SCNView: 0x100e03070 | scene=(null) sceneTime=0.000000 frame={{0, 0}, {480, 360}} pointOfView=(null)>>

For posterity, I should also point out that the other letters (AFOW etc.) are defined at the bottom of _subtreeDescription's output.

What do the values in _subtreeDescription output mean?

1 Answers