987443 - Rounding error of Zoom Widget %label

Status: RESOLVED FIXED

(Firefox :: Toolbars and Customization, defect)

Description

[Alice0775 White]

Steps To Reproduce.
1. Preparation
   set devtools.chrome.enabled = true in about:config
   Open Scratchpad (Shift+F4)
   Check Environment > Browser
2. Open any web page
3. Paste following code to Scratchpad and run
   ZoomManager.setZoomForBrowser(gBrowser.selectedBrowser , 0.95);
   FullZoom._applyZoomToPref(gBrowser.selectedBrowser);
4. Observe %lebel of Zoom Widget

Actual Results
 94%

Expected Results:
 95%

Comment 1

[Mike de Boer [:mikedeboer]]

Using the zoom +/- buttons I get the following values for `window.ZoomManager.zoom`:

zoom value: 1
zoom value: 0.949999988079071
zoom value: 1
zoom value: 0.8999999761581421
zoom value: 0.800000011920929
zoom value: 0.6700000166893005
zoom value: 0.5
zoom value: 0.30000001192092896
zoom value: 1
zoom value: 1.100000023841858
zoom value: 1.2000000476837158
zoom value: 1.3300000429153442
zoom value: 1.5
zoom value: 1.7000000476837158
zoom value: 2
zoom value: 1
zoom value: 1

This is on OSX, retina.

The `0.949999988079071` value is what I get when using Alice's STR. This lead to the following patch.

Comment 2

[Mike de Boer [:mikedeboer]]

Attachment: Patch v1: fix zoom button label rounding

Comment 3

[:Gijs (he/him)]

Comment on attachment 8396286 [details] [diff] [review]
Patch v1: fix zoom button label rounding

Review of attachment 8396286 [details] [diff] [review]:
-----------------------------------------------------------------

Math in JS is hard. :-(

Comment 4

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/integration/fx-team/rev/aa558a14a770

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/aa558a14a770

Comment 6

[Mike de Boer [:mikedeboer]]

Comment on attachment 8396286 [details] [diff] [review]
Patch v1: fix zoom button label rounding

[Approval Request Comment]
Bug caused by (feature/regressing bug #): Australis
User impact if declined: User might see an invalid zoom percentage for non-default zoom levels. It's rare, but theoretically possible.
Testing completed (on m-c, etc.): landed on m-c.
Risk to taking this patch (and alternatives if risky): minor.
String or IDL/UUID changes made by this patch: n/a

Comment 7

[Matthew N. [:MattN]]

https://hg.mozilla.org/releases/mozilla-aurora/rev/ce9cfb44f9c2

Comment 8

[Matthew N. [:MattN]]

https://hg.mozilla.org/releases/mozilla-beta/rev/76d6c9260ae6

Comment 9

[:Gijs (he/him)]

I don't think this is worth writing and running a testcase for.