Bug 190513 – [Cairo] Incorrect rendering for 135-deg skews

• Status: RESOLVED
• Resolution: FIXED
• Component: New Bugs

[Yoshiaki Jitsukawa]

Transforming with 135 deg skew results in incorrect rendering.

With a 135 deg skew, transformation matrix is { xx=1, xy=-1, yx=0, yy=1 } and here
the xScale becomes 0, which causes a division-by-zero.
https://github.com/WebKit/webkit/blob/523cf6b5bbafa7394699a0b3b52f13265174cff6/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp#L245

This behavior has been introduced with bug 154283.

[Yoshiaki Jitsukawa]

Quick test:
https://psdev-ext.jp.biz.playstation.net/orbis/vsh/testapp/xshin/transform_test.html

[Yoshiaki Jitsukawa]

Created attachment 352150 [details]
layout tests

[Yoshiaki Jitsukawa]

Created attachment 352152 [details]
Patch

[Yoshiaki Jitsukawa]

Provided R=(ctm.xx, ctm.xy, ctm.yx, ctm.yy), T=(ctm.x0, ctm.y0), D=(-dx, -dy),
the translation components (x0, y0) after cairo_translate(-dx, -dy) will be
 (x0, y0) = R*D + T
so D to zero (x0, y0) is:
 D = -R^-1* T

With (xy = 0, yx = 0), D is:
 D = -(x0, y0) * (yy, xx) / det: where det = xx * yy
so
 (dx, dy) = (x0 / xx, y0 / yy)

This is the same result as before.

[EWS Watchlist]

Comment on attachment 352152 [details]
Patch

Attachment 352152 [details] did not pass mac-ews (mac):
Output: https://webkit-queues.webkit.org/results/9549433

New failing tests:
fast/transforms/skew-y-135deg-with-gradient.html
fast/transforms/skew-x-135deg-with-gradient.html

[EWS Watchlist]

Created attachment 352153 [details]
Archive of layout-test-results from ews101 for mac-sierra

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews101  Port: mac-sierra  Platform: Mac OS X 10.12.6

[EWS Watchlist]

Comment on attachment 352152 [details]
Patch

Attachment 352152 [details] did not pass mac-wk2-ews (mac-wk2):
Output: https://webkit-queues.webkit.org/results/9549446

New failing tests:
fast/transforms/skew-y-135deg-with-gradient.html
fast/transforms/skew-x-135deg-with-gradient.html

[EWS Watchlist]

Created attachment 352154 [details]
Archive of layout-test-results from ews106 for mac-sierra-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews106  Port: mac-sierra-wk2  Platform: Mac OS X 10.12.6

[EWS Watchlist]

Comment on attachment 352152 [details]
Patch

Attachment 352152 [details] did not pass mac-debug-ews (mac):
Output: https://webkit-queues.webkit.org/results/9549511

New failing tests:
fast/transforms/skew-y-135deg-with-gradient.html
fast/transforms/skew-x-135deg-with-gradient.html

[EWS Watchlist]

Created attachment 352157 [details]
Archive of layout-test-results from ews112 for mac-sierra

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews112  Port: mac-sierra  Platform: Mac OS X 10.12.6

[EWS Watchlist]

Comment on attachment 352152 [details]
Patch

Attachment 352152 [details] did not pass ios-sim-ews (ios-simulator-wk2):
Output: https://webkit-queues.webkit.org/results/9549724

New failing tests:
fast/transforms/skew-y-135deg-with-gradient.html
fast/transforms/skew-x-135deg-with-gradient.html

[EWS Watchlist]

Created attachment 352164 [details]
Archive of layout-test-results from ews125 for ios-simulator-wk2

The attached test failures were seen while running run-webkit-tests on the ios-sim-ews.
Bot: ews125  Port: ios-simulator-wk2  Platform: Mac OS X 10.13.6

[EWS Watchlist]

Comment on attachment 352152 [details]
Patch

Attachment 352152 [details] did not pass ios-sim-ews (ios-simulator-wk2):
Output: https://webkit-queues.webkit.org/results/9550617

New failing tests:
fast/transforms/skew-y-135deg-with-gradient.html
fast/transforms/skew-x-135deg-with-gradient.html

[EWS Watchlist]

Created attachment 352167 [details]
Archive of layout-test-results from ews126 for ios-simulator-wk2

The attached test failures were seen while running run-webkit-tests on the ios-sim-ews.
Bot: ews126  Port: ios-simulator-wk2  Platform: Mac OS X 10.13.6

[EWS Watchlist]

Comment on attachment 352152 [details]
Patch

Attachment 352152 [details] did not pass win-ews (win):
Output: https://webkit-queues.webkit.org/results/9551304

New failing tests:
fast/transforms/skew-y-135deg-with-gradient.html
fast/transforms/skew-x-135deg-with-gradient.html

[EWS Watchlist]

Created attachment 352168 [details]
Archive of layout-test-results from ews205 for win-future

The attached test failures were seen while running run-webkit-tests on the win-ews.
Bot: ews205  Port: win-future  Platform: CYGWIN_NT-6.1-2.9.0-0.318-5-3-x86_64-64bit

[Michael Catanzaro]

Thanks!

You'll investigate why the EWS are failing?

[Yoshiaki Jitsukawa]

(In reply to Michael Catanzaro from comment #17)
> Thanks!
> 
> You'll investigate why the EWS are failing?

Yes, let me check.

[Yoshiaki Jitsukawa]

Created attachment 352286 [details]
diff image

Looks like solid color and gradient make slightly different results. The tests need to improve.

[Yoshiaki Jitsukawa]

Created attachment 352294 [details]
Patch

[Yoshiaki Jitsukawa]

(In reply to Yoshiaki Jitsukawa from comment #19)
> Looks like solid color and gradient make slightly different results. The
> tests need to improve.

10px border lines now cover the edges rendered (antialiased?) in a platform-specific way.

[Zan Dobersek]

Comment on attachment 352294 [details]
Patch

r=me

[WebKit Commit Bot]

Comment on attachment 352294 [details]
Patch

Clearing flags on attachment: 352294

Committed r237119: <https://trac.webkit.org/changeset/237119>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/45274028>