Spec: https://drafts.fxtf.org/css-masking-1/#ClipPathElement

Note in particular the discussion of clipPathUnits and later the statement that the display property does not apply to clipPath elements.

@tabatkins, it seems the sentence "User coordinates are sized equivalently to the CSS px unit." applies to any case where the SVG clip-path is used in CSS. And it's not entirely clear what the user space is for HTML objects. I presume it's the BorderBox coordinates, in px units.

This reminds me of  issue 373358 , which already has some discussion on what the "user coordinate space" might be. It also happens to start from the exact same tests (AFAICS) =).

IIRC, the reason <shape> and url(...) differ currently is because the former (always) uses the offset of the layer bounds (when resolving the shape) while the same offset isn't applied in a way such that it'd affect the local coordinate space in which the clip-path (url, reference) would be. 

The definition of the two SVG unit types, converted to the CSS box model, is over in the Images 4 delta spec <https://drafts.csswg.org/css-images-4/#paint-sources>.

It doesn't look like the spec has a good definition of which box to use as the bounds. I suggest following the clip-path default of border-box, which is a good approximation to what SVG does.

 Issue 373358  has been merged into this issue.

http://jsbin.com/soveso/edit is producing very odd results.

A guess would be that we apply the clip-path twice (once via PaintLayer and once via SVGPaintContext) for the root (outermost) <svg>. Try checking for isSVGRoot in the else-branch in SVGPaintContext::applyClipIfNecessary.

...and those two callsites will use two different references boxes (the oBB in the latter case, which will be <100, 100, 400, 400>.)

I bet that's it, yes. So the follow on fix for that might be not applying it in PaintLayer if the target is SVG.

I'd suggest the opposite, since that's we're heading (i.e things that have a CSS layout box uses PaintLayer while the rest of the lot does something else.) That's also how we deal with opacity and blend-mode for the outermost root.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e6cc64ba85ee2f7927578efb8d91641db367c2f0

commit e6cc64ba85ee2f7927578efb8d91641db367c2f0
Author: schenney <schenney@chromium.org>
Date: Thu Jun 23 17:24:46 2016

Fix positioning of CSS reference clips in composited layers.

When painting into composited scrolling layers, clip paths must use
an offset from the root location to account for the origin of the
the layer's paint coordinate system. SVG clips referenced by CSS,
with the default UserSpaceOnUse coordinate system were not applying
this offset as required. When the clip is in ObjectBoundingBox
coordinates the offset was applied as a side effect of the object's
bounding box.

This patch corrects the position by adding the necessary offset when
the clip coordinate system is UserSpaceOnUse.

R=fs@opera.com
BUG= 617265 

Review-Url: https://codereview.chromium.org/2078343005
Cr-Commit-Position: refs/heads/master@{#401642}

[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/LayoutTests/compositing/overflow/accelerated-scrolling-with-clip-path-text.html
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/LayoutTests/compositing/overflow/accelerated-scrolling-with-clip-path.html
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/LayoutTests/compositing/overflow/accelerated-scrolling-with-clip-reference.html
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/LayoutTests/css3/masking/clip-path-reference-userSpaceOnUse.html
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/Source/core/paint/SVGClipPainter.cpp
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/Source/core/paint/SVGClipPainter.h
[modify] https://crrev.com/e6cc64ba85ee2f7927578efb8d91641db367c2f0/third_party/WebKit/Source/core/paint/SVGPaintContext.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee

commit 7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee
Author: Rebaseline Bot <blink-rebaseline-bot@chromium.org>
Date: Thu Jun 23 19:02:25 2016

Auto-rebaseline for r401642

https://chromium.googlesource.com/chromium/src/+/e6cc64ba8

BUG= 617265 
TBR=schenney@chromium.org

Review URL: https://codereview.chromium.org/2097613002 .

Cr-Commit-Position: refs/heads/master@{#401668}

[modify] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/linux/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.png
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/linux/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.txt
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/linux/virtual/prefer_compositing_to_lcd_text/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.png
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/linux/virtual/prefer_compositing_to_lcd_text/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.txt
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/mac/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.png
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/mac/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.txt
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/mac/virtual/prefer_compositing_to_lcd_text/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.png
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/mac/virtual/prefer_compositing_to_lcd_text/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.txt
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/win/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.png
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/win/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.txt
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/win/virtual/prefer_compositing_to_lcd_text/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.png
[add] https://crrev.com/7e91aa148b5d7b40b1f5035d6f2e6d805ef412ee/third_party/WebKit/LayoutTests/platform/win/virtual/prefer_compositing_to_lcd_text/compositing/overflow/accelerated-scrolling-with-clip-path-text-expected.txt

What's left to do here?

We still have the issue that defs are not available to CSS when defined inside "display: none" SVG content. According to spec they should be.

It could be a separate bug.

We have issue 258029. (We also some seemingly conflicting bugs, like issue  231552...)

The other bugs aren't really conflicting. It's more that we screw it up in different ways for different situations.

And given I migrated the bugs, it's sad I don't remember. I'll close this one in favor of the others.