1659492 - Implement true smooth zooming on pdf.js

Status: RESOLVED FIXED

(Firefox :: PDF Viewer, enhancement, P1)

Description

[Kartikaya Gupta (email:[e-mail])]

Some types of inputs (e.g. doing a pinch-gesture on a touchscreen, a macOS trackpad, or high-precision windows/linux trackpad) should do a "smooth" zoom on pdf.js. Currently (as of bug 1643508) touchscreen pinches will do nothing, and the trackpad pinches will do a "stepwise" zoom, where the zoom factor goes up/down by 1.1x every so often.

This bug tracks implementing a "smooth" zoom where the zoom of the document tracks the pinch much more closely.

Comment 2

[Brendan Dahl [:bdahl]]

For someone implementing this, pdf.js already supports doing a CSS zoom where the canvas is scaled by using a CSS transforms first, then doing a full re-draw. We could reuse that by first using CSS zoom, then when the pinch zoom is done, re-draw.

Comment 3

[Kartikaya Gupta (email:[e-mail])]

Can you point me to the APIs that one would use to do this? I was trying to figure out the various setScale-related functions in base_viewer.js but it would probably be easier if you can say which ones would be appropriate here.

I think the only other significant change would be ensuring that the UI thingy that shows the current scale factor is updated appropriately, which I imagine shouldn't be too hard.

Comment 4

[Brendan Dahl [:bdahl]]

If you search for zoomLayer in https://github.com/mozilla/pdf.js/blob/master/web/pdf_page_view.js you'll find the relevant bits. You can also enable only CSS zoom https://github.com/mozilla/pdf.js/blob/ebb903e5067b15081d2cf8e953996bf5ffb8da72/web/app_options.js#L147

Comment 5

[MarjaE]

I have a neuro issue where zooming animations reliably give me migraines and motion sickness, and smooth animations such as smooth scrolling, ease in-out, etc. also reliably give me migraines and motion sickness.

Since it's hard to avoid accidental zooming, I fear the combination will make me vomit onto the keyboard.

Comment 6

[Timothy Nikkel (:tnikkel)]

You know about the about:config pref apz.allow_zooming to disable normal pinch zooming?

Comment 7

[MarjaE]

Not pdf-specific, but there are a lot of sites which either zoom on mouseover, or zoom if users scroll, or zoom if users input data.

Comment 8

[Botond Ballo [:botond]]

In pdf.js, we should be able to check the system's "prefers reduced motion" setting, and zoom in fixed increments (e.g. go from 100% directly to 120% rather than smoothly changing the zoom level from one to the other) in that case.

Comment 9

[MarjaE]

Another option would be to check general.smoothscroll, which has a front-end under about:preferences.

Comment 10

[Botond Ballo [:botond]]

My understanding is that this bug was tracking making pinch-zooming smooth with both touchscreens and touchpads:

(In reply to Kartikaya Gupta (email:[e-mail]) from comment #0)

Some types of inputs (e.g. doing a pinch-gesture on a touchscreen, a macOS trackpad, or high-precision windows/linux trackpad) should do a "smooth" zoom on pdf.js. Currently (as of bug 1643508) touchscreen pinches will do nothing, and the trackpad pinches will do a "stepwise" zoom, where the zoom factor goes up/down by 1.1x every so often.

This bug tracks implementing a "smooth" zoom where the zoom of the document tracks the pinch much more closely.

Touchscreen zooming works nicely now, but touchpad pinch-zooming (tested on Linux Wayland) is still stepwise (zooms in 10% increments).

Calixte, should we reopen this?

Comment 11

[Calixte Denizet (:calixte)]

Yep you're right we must fix the pinch-to-zoom on a trackpad to be complete.

Comment 12

[Calixte Denizet (:calixte)]

Attachment: pr 15909: Add support for smooth pinch-to-zoom on a trackpad (bug 1659492)

Comment 13

[Kartikaya Gupta (email:[e-mail])]

For me on macOS 2023-01-09 nightly using the trackpad to zoom on a PDF zooms the entire content area, including the PDF toolbar component. That's not what I would expect (and not what I intended when I filed this bug). But I don't know, maybe that's the intended behaviour now?

Comment 14

[Calixte Denizet (:calixte)]

:kats, I filed a bug about that:
https://bugzilla.mozilla.org/show_bug.cgi?id=1809080.
It should be fixed in nightly this week.

Comment 15

[Botond Ballo [:botond]]

(In reply to Calixte Denizet (:calixte) from comment #11)

Yep you're right we must fix the pinch-to-zoom on a trackpad to be complete.

Thanks! Confirmed to be working well on Linux Wayland as well now.