Add smooth scrolling

[Yanpas]

Feature request: add smooth scrolling. (small detail: it would be fine to have precise scrolling on touchpads)
I guess that it would be possible to add this feature after migration to QT5 https://doc.qt.io/qt-5/qabstractscrollarea.html

[Adam Reichold (adamreichold)]

Hello Yanpas,

I am not sure which feature of the scroll area shipped with Qt 5 you are referring to, but scrolling is already per pixel or "smooth" with Qt 4. (Of course, pressing the arrow keys or buttons will usually not scroll by only a single pixel.)

If you are referring to reimplementing Qt's input event handling to change how the scroll area reacts to certain input devices, I have to say that I am certain that this is out of scope for a simple application like qpdfview.

Best regards, Adam.

[Yanpas (yanpaso)]

I'm using qpdfview 0.4.14 from Xubuntu 16.04 and the scrolling is not smooth at all. Every scroll of mouse wheel instantly moves page to 1-2 cm up or down.

[Adam Reichold (adamreichold)]

Hello again,

how input events are synthesized, i.e. how many mouse wheel events with how large a delta value are generated, depends on the graphical environment and the drivers used. And how Qt's QScrollArea reacts to these events is again something that I do not want to reimplement as I am sure it is out of scope for qpdfview.

Maybe you can configure your X server's input handling to generate different mouse wheel events?

Best regards, Adam.

[Yanpas (yanpaso)]

Precise and smooth scrolling works perfect in Chrome and Evince. Maybe something wrong with my libraries / DE. What DE and distro do you use?

[Adam Reichold (adamreichold)]

Hello again,

I use different distributions and different desktops and I would say that scrolling in qpdfview works as it does it other Qt-based applications. As discussed above, there are different ways to implement scrolling but I do not think that qpdfview should implement its own method and if you are sure that how scrolling is implemented in QScrollArea should change, then that change should probably happen within Qt itself.

Best regards, Adam.

[Catalin Hritcu (catalin-hritcu)]

I'm on Manjaro Xfce (freshly installed with the default configuration) and scrolling in qpdfview happens for me in large increments (1-2cm). This is very annoying and it doesn't happen in the other applications I've tried (Chrome, Xfce Terminal, etc). I'm new to Xfce, so I don't really where to look to try to customize this. Any suggestions?

[Catalin Hritcu (catalin-hritcu)]

Let me quickly retract part of what I just said. It does in fact happen in the other applications, just that at least applications like Chrome "smoothen out" the movement by doing the big scroll incrementally, while applications like qpdfview do the movement all at once in 1-2cm increments. Ideally there would be a way to stop this big increment scrolling. I looked in xinput, but couldn't tell if any of the options there could help:

```
$ xinput list-props 9 | grep Scroll
 libinput Natural Scrolling Enabled (275): 0
 libinput Natural Scrolling Enabled Default (276): 0
 libinput Scroll Methods Available (277): 0, 0, 1
 libinput Scroll Method Enabled (278): 0, 0, 0
 libinput Scroll Method Enabled Default (279): 0, 0, 0
 libinput Button Scrolling Button (280): 2
 libinput Button Scrolling Button Default (281): 2
 libinput Horizontal Scroll Enabled (292): 1
```

Anyway, unless someone here has a quick idea, I will ask this on some other forum (although I'm still wondering what would be a good place).

[Catalin Hritcu (catalin-hritcu)]

Let me also mention that I'm using a mouse (Logitech M705) that has a scrolling wheel that has two modes that can be changed by a physical switch: (1) incremental scrolling and (2) continuous scrolling with point accuracy. The problem happens in mode (2), where I would expect to be able to scroll "little by little", not only in large increments, which in qpdfview are super large (1-2cm).