calibre
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kovidgoyal
Use smooth scroll in viewer on mouse wheel scroll
Summary
Currently, the calibre viewer has smooth scrolling if you press the Up/Down keyboard keys, but not if you scroll using your mouse wheel. This is regardless of the orientation of the text. This PR attempts to use the same smooth animating system as keyboard press for mouse wheel events. This was previously requested here.
Implementation
Instead of calling scroll_by_in_block_direction on mouse scroll, we now call into the ScrollAnimator class that is used already by the Up/Down keyboard shortcuts. To specify how much we want to scroll by, a new argument was added to scroll_animator.start().
Furthermore, scroll_by_and_check_next_page checks whether the scroll resulted in a chapter flip. Unfortunately we can't use the same function anymore since by using ScrollAnimator, we lose access to calling arbitrary checks upon finishing the scroll. Fortunately though, ScrollAnimator already checks whether we need to move to the next/previous spine item, so we can remove the need to call scroll_by_and_check_next_page!
Tested
Tested scrolling with keyboard and mouse on one vertical and horizontal book each.
This makes scrolling with a touchpad much worse, as noted in the original MR thread. If you want to do this, it should only be done for DOM_DELTA_LINE. And possibly even then have an option to turn it off/on in the scrolling behavior section of the viewer preferences.
Ouch, I hadn't tested with a touchpad. I'll look into adding a config option as you say, and likely limit it to _LINE only. May I ask why you think smooth scroll shouldn't be used with DOM_DELTA_PAGE? Presumably, that can also benefit from smooth scroll.
What would page based smooth scrolling look like? You want to animate the page transition? You certainly cant turn pages continuously, since you have to give the user time to read the page.
I've tested and researched a bit more and it seems that both my mouse and trackpad emit a DOM_DELTA_PIXEL, and in fact, based on some reading, it seems Chromium (which is underneath QtWebEngine) will always emit either a calculated DOM_DELTA_PIXEL or a DOM_DELTA_PAGE regardless of how the OS is configured to send scroll events (Chromium source code for wheel event & discussion on Mozilla about how they are the only browser using DOM_DELTA_LINE).
There is no way to detect whether a mouse or trackpad is being used at all.
We can have an option to enable smooth scroll on all possible DELTA modes (and mouse users can opt-in to this), but I feel it might be better to abandon this PR.