This error happens usually when the code is trying to transform a singular 3x3 matrix which is is considered a mathematical violation. So I think there should be some condition to check whether the matrices has a determinant of zero.

ccameron@, any idea what this might be? There's only a couple of places we use CGAffineTransformInvert, and one of them (https://cs.chromium.org/chromium/src/skia/ext/bitmap_platform_device_mac.cc?q=%22CGAffineTransformInvert%22&sq=package:chromium&l=90&dr=C) looks a little suspicious to me. What do you think?

More likely being caused by something in Cocoa. Two suggestions from StackOverflow

First:

  I once had this error cause by mistake was setting a font with size 
  0 when using [UIFont fontWithName:size:] for a UILabel.

Second:

  "CGAffineTransformInvert: singular matrix" seems to come up when
  layoutSubViews: runs on a view (such as UIScrollView or UILabel) that
  has a frame of size (0,0).

Dropping priority, marking available.

Since this happens to every renderer, I used lldb to figure out the emitter of the warning. Looks like an issue at the intersection of Skia and CoreText/CoreGraphics.

"""
(lldb) bt
* thread #1: tid = 0x57ef1, 0x00007fffd37c2a44 CoreGraphics`CGAffineTransformInvert + 59, name = 'CrRendererMain', queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
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    frame #190: 0x000000012454b287 libcontent.dylib`RunNamedProcessTypeMain + 599 at content_main_runner.cc:418
    frame #191: 0x000000012454d176 libcontent.dylib`Run + 1462 at content_main_runner.cc:785
    frame #192: 0x000000012454aaed libcontent.dylib`ContentMain + 349 at content_main.cc:20
    frame #193: 0x000000010e0e2843 libchrome_dll.dylib`ChromeMain + 83 at chrome_main.cc:85
    frame #194: 0x000000010942dd7c Chromium Helper`main + 780 at chrome_exe_main_mac.c:85
    frame #195: 0x000000010942da64 Chromium Helper`start + 52
"""

I think this usually happens when a text size of zero is requested. Skia can't ask CG directly for a text size of 0 (you'll end up with 12 or something like that instead), so we ask for some size and then transform it down to 0.

The documentation for CGAffineTransformInvert at https://developer.apple.com/library/mac/documentation/GraphicsImaging/Reference/CGAffineTransform/index.html#//apple_ref/c/func/CGAffineTransformInvert explicitly states that if the transform cannot be inverted it will be returned unchanged. There's no point wasting time checking to see if it can be inverted, and then have CGAffineTransformInvert again check (with a different method and tolerances, so the initial check may be for nothing anyway). That CGAffineTransformInvert as a library function is writing to stdio or stderr directly seems bad form, it should get fixed.

Is there someone on the team who would be best to open a radar against Apple to remove this rather annoying message that the function is doing what it says it does? I'm also not sure of current way of marking this issue as an external dependency.

This happens every time I navigate away from the NTP to google.com. Given that we control all of these domains, I would hope that we would never request a text size of zero. I'm guessing there's a bug somewhere. Can you look into the Skia side, and if the issue isn't there, we can find an appropriate Blink person to continue investigating?

There's no designated person for filing radars. Instructions are here: https://g3doc.corp.google.com/company/appledev/book/apple/bugs/index.md?cl=head

The following revision refers to this bug:
  https://skia.googlesource.com/skia.git/+/1f0e78ddf94f6259e8bbfb403b55c8eeedac390c

commit 1f0e78ddf94f6259e8bbfb403b55c8eeedac390c
Author: bungeman <bungeman@google.com>
Date: Tue Aug 23 20:19:01 2016

SkScalerContextRec::computeMatrices to return status.

When computing the matricies for a scaler context, there is a special
case when the matrix is determined to be singular. No port properly
handles zero sized text, so we detect this case and return a 'normal'
text size and a zero matrix for all computed transformations. This
CL causes computeMatricies to return 'false' in this case.

This is used in the constructor of SkScalerContext_Mac in order to
avoid calling CGAffineTransformInvert on non-invertible transformations.
CGAffineTransformInvert documents that if the transform is
non-invertible it will return the passed transform unchanged. It does
so, but then also prints a message to stdout. Since the information is
already available to avoid this chatty behavior, use it to keep things
quiet.

BUG= skia:3231 , chromium:630169 
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2276583003

Review-Url: https://codereview.chromium.org/2276583003

[modify] https://crrev.com/1f0e78ddf94f6259e8bbfb403b55c8eeedac390c/src/core/SkScalerContext.cpp
[modify] https://crrev.com/1f0e78ddf94f6259e8bbfb403b55c8eeedac390c/src/core/SkScalerContext.h
[modify] https://crrev.com/1f0e78ddf94f6259e8bbfb403b55c8eeedac390c/src/ports/SkFontHost_mac.cpp

Awesome, thanks! I take it this is fixed?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/94267418aa8cd1f48f99ec9aa83b9908cc804484

commit 94267418aa8cd1f48f99ec9aa83b9908cc804484
Author: skia-deps-roller <skia-deps-roller@chromium.org>
Date: Wed Aug 24 01:37:46 2016

Roll src/third_party/skia/ da19f6f3b..ae6377c08 (6 commits).

https://chromium.googlesource.com/skia.git/+log/da19f6f3b5f1..ae6377c08e5c

$ git log da19f6f3b..ae6377c08 --date=short --no-merges --format='%ad %ae %s'
2016-08-23 msarett Make singleton SkColorSpaces thread safe
2016-08-23 bsalomon Remove SkPixelRef::getTexture() GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2264293003
2016-08-23 mtklein GN: extract optional() as a template and use for giflib-dependent code
2016-08-23 mtklein GN: Fix up Ganesh native interface hooks.
2016-08-23 csmartdalton Skip non-AA intersect rects in GrReducedClip
2016-08-23 bungeman SkScalerContextRec::computeMatrices to return status.

BUG= 630169 

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
TBR=bungeman@google.com

Review-Url: https://codereview.chromium.org/2274773002
Cr-Commit-Position: refs/heads/master@{#413930}

[modify] https://crrev.com/94267418aa8cd1f48f99ec9aa83b9908cc804484/DEPS

Marking as fixed. We already have the information we need to make a determination not to call CGAffineTransformInvert, so the added complexity is just an extra conditional branch. I'll see what can be done to get CoreGraphics to stop writing to stdout, but at least we're avoiding the case where it does so.

@Comment 6: it turns out that zero sized text is more common than one would hope. I know of at least one situation where it's done on purpose (to force use of a webfont). There's also those doing it to force whitespace to zero width, see https://css-tricks.com/fighting-the-space-between-inline-block-elements/#article-header-id-3  . Doing a search for "font-size: 0" turns up a somewhat disturbing number of results.