1427220 - <svg:text>s with same pos but diff stroke not on top of each other

Status: UNCONFIRMED

(Core :: SVG, defect, P3)

Description

[Philipp Pief]

Attachment: stroke_demo.html

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20171218174357

Steps to reproduce:

1. Go to https://bl.ocks.org/Herst/raw/a304caf946e59a7e34c24bd828fa0b3a/ or open the attached test case.

2. Click on the "paint-order" checkbox to switch between drawing the text twice to get the outline/glow effect and look for changes.


Actual results:

There is a difference between the two states toggled through the checkbox. It looks like in the case with the two <text> elements on top of each other (instead of using paint-order) the two text elements are not exactly on top each other (the black text is not centered inside the bright outline text with the thicker stroke).

See also the screenshots. Reproduced on Windows and Linux.


Expected results:

The two cases should be indistinguishable, as is the case in Google Chrome (see screenshot).

Comment 1

[Philipp Pief]

Attachment: Windows

Comment 2

[Philipp Pief]

Attachment: Linux

Comment 3

[Philipp Pief]

Attachment: Google Chrome

Comment 4

[Robert Longson [:longsonr]]

This looks like antialiasing at work. I don't think it's a bug.

Comment 5

[Philipp Pief]

Attachment: Linux (detail)

> This looks like antialiasing at work.

There is indeed an antialiasing difference between the two cases on Windows, in the double paint case subpixel antialiasing is used while in the paint-order there is only greyscale AA (as is the case in Linux in either case). I would argue that this is unexpected as well which is why I filled bug 1400663 in which IMHO you didn't quite understand the problem as well (I should have been more clear).

To the problem, horizontal antialiasing cannot account for vertical differences and like I said in Chrome both case look the same. Please have a look at the attached detail view to see how the *vertical* alignment is not correct.