Change Dolphin's appearance alone

I’m wondering if there’s a way to customize Dolphin without affecting other KDE or Qt apps, and without changing the source code.

I would like to increase the thumbnail size beyond the maximum zoom level and actually found a way of doing so by assigning a higher value to QT_SCALE_FACTOR when running it, but then I have to compensate for everything other than the thumbnails gettings bigger (icons, text, toolbar, header) and so far the aspects I can change I can only do so through the global settings, thus changing the appearance of all other Qt and KDE apps.

My hope is that there’s some sort of configuration file I could use at run time, kind of like when you apply a userstyle to a website you don’t own except for desktop Qt apps, giving you access to all Qt parameters that don’t exist as environment variables, but I couldn’t find such a thing because all my search results point to source code development rather than code for already installed apps.

If such a thing doesn’t exist, so be it. I’ll leave Dolphin at its default style.

Alter the .desktop file or launcher to look a bit like

Exec=env QT_SCALE_FACTOR=2  dolphin %u

Dolphin has a “Zoom” slider at the bottom, does that not do what you want to achieve?

Thanks but knowing how to zoom is not my issue. I’m talking about larger thumbnail sizes for HiDPI displays, like Thunar does since v4.18 (although it’s a broken feature currently). This is why I’d like to change Qt/KDE settings on a per-application basis and hopefully even per-instance basis. I have low expectation that such a possibility exists at this point but that’s ok. I frequently jump between Linux file browsers depending on my task and will continue doing so. Somehow they all complete each other for me despite each having their drawbacks.

Thanks but that’s not my issue. I know how to change the variable when running it. My problem is adapting the size of elements other than thumbnails to compensate for the increase in global scale.

In general it’s recommended to use full screen scaling to make the entire system adapt to a high DPI screen, rather then applying hacks to invididual apps. Doing that is likely to cause pain in the long term.

Thanks. I’m using 2x scaling, which is comfortable for me to read. I’m looking to get thumbnails roughly 3x but when I do so globally, the text and icons get unnecessarily big.
For some other Qt apps I need to save screen space for the viewport and can’t afford to have large buttons and text. For these I use 1.5 scale or even 1. I understand applying hacks to invididual apps is not recommended but it’s just the better deal for me. Programs come in all shapes and forms and have all kinds of purposes. Sometimes global settings don’t align with them or how we use them all.

It’s ok if what I’m asking doesn’t exist. If you are curious to find out as well or know the answer from the top of your head, by all means tell me all about it but otherwise, by even more means have a good free time or get to whatever much more pressing issues you have. If I really need to change the size of thumbnails alone, I’ll look into the source code and try to make a custom build. And if I succeed I’ll share the patch here.

I just noticed that QT_FONT_DPI can work with values below 96 only if you set QT_AUTO_SCREEN_SCALE_FACTOR=0. So that’s one step closer.

Now the main issue is the vector icon sizes, though that’s where I have the most doubts because they are much more specific KDE settings.

At this point I would recommend that you submit a feature request for Dolphin at requesting that the maximum thumbnail size be made larger.