595209 - scaling svg text causes it to be unreadable

Status: RESOLVED FIXED

(Core :: SVG, defect)

Description

[ben hockey]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.9) Gecko/20100824 Firefox/3.6.9 ( .NET CLR 3.5.30729)
Build Identifier:  Mozilla/5.0 (Windows NT 5.1; rv:2.0b5) Gecko/20100101 Firefox/4.0b5

using dojo's gfx library (dojox.gfx) i create an svg surface and add some text to it.  when the surface is resized, the text is unreadable - blurry.

Reproducible: Always

Steps to Reproduce:
1. load the attached test file (note the text 'abc' is clear)
2. click the 'click to resize' button (note the text is very blurry)
3. click the 'click to resize' button again (note the text is clear)
Actual Results:  
after the first resize, the text is very blurry.

Expected Results:  
the text should be clear

Comment 1

[ben hockey]

Attachment: a self contained test case to demonstrate the problem

Comment 2

[Robert Longson [:longsonr]]

You should probably use fill rather than stroke to draw text.

Comment 3

[Robert Longson [:longsonr]]

Even allowing for that the trunk display is odd.

Comment 4

[Boris Zbarsky [:bzbarsky]]

minimal testcase without the dojo goop would be nice...

Comment 5

[ben hockey]

Attachment: testcase, no dojo

a test case without dojo.  it seems the cause of the problem is the combination of using stroke and rotate on the text element.  commenting out the lines for either one causes the expected result but the combination causes the error.

Comment 6

[ben hockey]

Attachment: testcase, no dojo (without console.log)

sorry... left a console.log in the last one which meant that firebug had to be enabled to see this working.  removed the console.log so you don't need firebug enabled

Comment 7

[Boris Zbarsky [:bzbarsky]]

Thanks, confirming.  That click handler should really be idempotent; the fact that it's not is totally bogus.

Comment 8

[Takeshi Kurosawa :takenspc]

We call CharacterIterator::SetupFor() which rescales stroke-width in nsSVGGlyphFrame::AddCharactersToPath() for each glyph.
As a result we rescale stroke-width multiple times.

http://mxr.mozilla.org/mozilla-central/source/layout/svg/base/src/nsSVGGlyphFrame.cpp#1639

Comment 9

[Takeshi Kurosawa :takenspc]

Attachment: Reftest

Convert the attachment to reftest

Comment 10

[Takeshi Kurosawa :takenspc]

Attachment: Patch

Add Save()/Restore() for each iteration.

Comment 11

[Boris Zbarsky [:bzbarsky]]

Hmm.  So with this patch we'll save/restore for every single glyph in SVG text?  Is that reasonably cheap?

Comment 12

[Robert Longson [:longsonr]]

Echoing bz, why can't we Save/Restore outside the loops?

Comment 13

[Takeshi Kurosawa :takenspc]

Attachment: Patch

Yeah, we should save/restore outside the loop.

Comment 14

[Robert Longson [:longsonr]]

Why doesn't this affect textPaths or text with multiple lengths or rotations. If it does then your Save/Restore needs to go round the DirectTextRun... calls too.

On top of that can you use gfxContextAutoSaveRestore, then you won't need the restore call. See nsSVGInnerSVGFrame.cpp for usage.

Comment 15

[Robert Longson [:longsonr]]

Attachment: patch

When we go via the placed glyphs path - always for text-paths or as in the example when there is a rotation, we apply the line width scaling factor for each character rather than just once.

This bug has been around for a very long time, it's much more noticable now that we use the place glyphs code patch for ordinary text rather than just text-paths though.

Comment 16

[Robert Longson [:longsonr]]

Attachment: patch

part of another patch crept into the previous version

Comment 17

[Robert Longson [:longsonr]]

Attachment: hg changeset patch

Comment 18

[Robert Longson [:longsonr]]

Attachment: hg changeset patch

Comment 19

[Daniel Holbert [:dholbert]]

Landed patch: http://hg.mozilla.org/mozilla-central/rev/c428371144df
and tests:    http://hg.mozilla.org/mozilla-central/rev/ddfa6625b645