Libgdx, Setting the full screen resolution during runtime causes application to render at the wrong size - libgdx

Question

I am only using the desktop Application, no mobile.
I am experimenting with letting the user set the screen resolution during run time. I give him the Display Modes available and he applies one. This part actually works. The problem occurs when i save this mode and try to set this display mode the next time they launch the game.
I am using preferences to store the mode the user selected. I am unable to access preferences before the Create method in my Game class, or in the DesktopLauncher Object, where you normally set up the config file and pass it into the application. So my DesktopLauncher looks like this.
val config = Lwjgl3ApplicationConfiguration()
config.setFullscreenMode(Lwjgl3ApplicationConfiguration.getDisplayMode())
Lwjgl3Application(MainGame(), config)
I use the current screen resolution on the creation of the application. Then in my Create method in my MainGame class i get the mode they set from preferences and i set it like so...
override fun create() {
var modes = Gdx.graphics.displayModes.toList()
val mode = Gdx.graphics.displayMode
val preference: Preferences = Gdx.app.getPreferences("screenPreference")
val screenWidth = preference.getInteger("width", mode.width)
val screenHeight = preference.getInteger("height", mode.height)
val refreshRate = preference.getInteger("refreshRate", mode.refreshRate)
modes = modes.filter { it.width == screenWidth }
modes = modes.filter { it.height == screenHeight }
modes = modes.filter { it.refreshRate == refreshRate }
if (modes.isNotEmpty()) {
Gdx.graphics.setFullscreenMode(modes[0])
}
....
}
To summarize i get the list of modes, i pull from preferences what was set last, and i filter the list according to what was in preferences. This should leave one item left in the list and i apply it. If for some reason the list is empty, then i don't set it, or there is no preference set i just apply the current mode again.
This is where the weird stuff happens. I have checked all the numbers when creating my screens and cameras, and they are all correct. I do receive the correct resolution, but the application doesn't render correctly. Below are a couple examples of what happens.
In the first image you see the bounds of the application to the screen. My application only renders in the bottom corner, and the rest is black. What happened to achieve this effect is i started the application with a smaller resolution than my native resolution, so 1280x1024, then in my create method i set the application full screen mode to 1920x1080 before building the rest of my application. I have checked my cameras and my viewports, and they all have the resolution 1920x1080, but the image is not filling the entire screen.
And a second.
This one is what happens when i reverse the settings. So i start at native resolution 1920x1080, and in my create method i set it to 1280x1024, again before creating the rest of my application. This gives me black bars on both sides of the image like id expect, but the application is HUGE, and only a portion of it fits in the window, the rest goes out of bounds, as depicted by the dotted lines.
It will remain like this the entire time, unless i change the resolution while the application is running, it will then correct itself for the rest of the applications life.
I am confounded by this effect i am getting, and am looking for an answer as to why, or how to fix it.

Answer 1

I found the issue that was causing the image to render incorrectly. I was setting the display mode in the create() function in my main game class. This function is not run on the rendering thread, and you do not want to use Gdx.graphics on anything other than the rendering thread, as described in the libgdx wiki https://github.com/libgdx/libgdx/wiki/Threading
There is a function where you can pass in a lambda to be run on the rendering thread.
Gdx.app.postRunnable {
Gdx.graphics.setFullscreenMode(Gdx.graphics.getDisplayMode(modes[0]))
}
After passing that into postRunnable the game renders correctly on launch.