In Dolphin, text file previews are enabled, but all thumbnails for .txt files blank.

[ocalhoun]

Text file previews are one of the big reasons I switched to linux, actually.

And, at first, I turned on the option to show previews of text files and it worked perfectly. Now that I've restarted the computer a few times, though, I'm starting to have some issues with it.
Standard text files (with a .txt extension or no extension at all) are showing a blank preview image now. It is still attempting to preview them -- the option to show previews for text files is still turned on, and it's showing a preview of a blank document instead of the text file that exists. It's happening for all folders everywhere, including the desktop.
It is still showing proper previews for certain files, though: if I rename the text file as a .cfg or .ini for example, the preview loads and works perfectly. But if I rename the same file back to .txt, the preview goes blank again. (And those are using the same previewer: .cfg files stop showing previews if I turn off the option to preview text files.)

Screenshots:
These three files are exactly the same, just with different names.
Sometimes, I'm randomly getting this:


Most of the time, I get this:

[ocalhoun]

Maybe there's a cache somewhere that needs deleting? Where would that be?

[ocalhoun]

New development!

The text previews are NOT blank. They're showing the correct text ... with white text on a white background. If you open the second screenshot there in an image editor, you can change the colors and actually see the (outline of the) text, matching the .cfg and .ini files.

So the question becomes ... how do I change the text and/or background color of the text file preview thumbnails? (Editing title to reflect this.)

[DoYouKubuntu]

So the question becomes ... how do I change the text and/or background color of the text file preview thumbnails? (Editing title to reflect this.)

I believe that's set in your System Settings. It may be a function of the theme you're using, or it may be user-controllable. Try going to System Settings | Appearance | Colors and see if that answers the question. You should be able to edit whichever set you're using; hover over your set with your mouse, and you should see an 'edit' icon appear; use that to adjust your settings. If that's not it, then it's probably defined by the theme or style you're using. For example, under System Settings | Appearance | Application Style, again, hover over your style and see if it can be edited. If none of that works...someone else will have to chime in!

[ocalhoun]

Thanks! I didn't know you could hover over the color scheme to change it's details!
I feel like what I need has got to be in there somewhere ... the problem is that there are a LOT of colors to change in there ... and none of them are labeled 'thumbnail' anything. It's going to take a lot of experimentation to figure out which colors are actually being used in the text file thumbnails.

Edit:
Okay, well this is kind of bizarre.
First of all, I tried just selecting different color schemes, including some light-colored ones. None of it helped the thumbnails, even after refreshing the view to regenerate thumbnails and even creating new text files to ensure that it couldn't be using an old cached thumbnail. (That's the same testing procedure I used after every try.)
Then I tried making a copy of the breeze dark color scheme, and in the copy, I changed every white-ish color to bright green instead.
Eureka! The text in text file thumbnails turned bright green! (Not the white background, though. Apparently the white background color will never change.)
I then changed back to the standard Breeze Dark color scheme to start finding out exactly which color controls that text color ... and that's when it gets weird.
The text in text file previews is still green, even after changing to the standard Breeze Dark color scheme, even after refreshing the view, even after creating new files with new thumbnails.
Which ... I suppose that's an improvement vs white-on-white, but it's quite bizarre that the thumbnail color scheme sometimes can be changed by the system color scheme, but other times it does not respond to those changes.

Edit again:
Okay, starting to make some sense. There seems to be a substantial delay between applying the color settings and those settings actually being applied to thumbnails.
Unfortunately, this delay makes it extremely tedious to try and experiment to find out which color controls the thumbnail text color.
I'm going to try setting my experimental color scheme to all kinds of crazy colors ... which will hopefully allow me to identify the pertinent color.

[ocalhoun]

After further experimentation with the color schemes, I have learned some important things:

1: You can get the text file thumbnail color to change to the system theme color faster by selecting the window with your thumbnails in it and holding down F5 for a few seconds.

2: The background color of the text file thumbnail cannot be changed.

3: The color of the text in the thumbnail is controlled by the 'View Text' color of the system's color scheme! Unfortunately, so is a lot of other things. Still ... now all I have to do is change the 'View Text' color to a color that looks acceptable on both a light and a dark background. Wish me luck!

We can consider this issue solved now, more or less (though it still would be nice to find a way to change the thumbnail background color or change the thumbnail text color without changing any other system colors.)

[DoYouKubuntu]

I'm glad you've made some progress! It's funny about the 'hover' color thing--I didn't know either, until I stumbled upon it one time. Being able to adjust its settings is so nice!

Being me, I refuse to believe that anything can't be done on Linux, so I'm convinced that the background color can be changed--we just don't know how yet. When I have some time, I'll poke around a bit, too, and see if I can find its magical setting. If you do, please post! It's always helpful for others to see how things were solved.

[ocalhoun]

Well, if it can be changed, it's not through the system color settings. Maybe it's hard-coded somewhere in the code that generates previews?
I changed *every* white or white-ish color in the color settings, and it never changed the background color of the file previews.