Interface gets extra pixel - libgdx

Question

I made an interface for a game, using extended viewport and when i resize the screen the aspect ratio changes and every element in scene is scales, but when this happens this is what i get :
This is the most annoying issue i dealt with, any advice ? I tried making the tower n times bigger and then just setting bigger world size for the viewport but same thing happens, idk what is this extra pixels on images..
I'm loading image from atlas
new TextureRegion(skin.getAtlas().findRegion("tower0"));
the atlas looks like this:
skin.png
size: 1024,1024
format: RGBA8888
filter: Nearest,Nearest
repeat: none
tower0
rotate: false
xy: 657, 855
size: 43, 45
orig: 43, 45
offset: 0, 0
index: -1

Answer 1

In the third picture, you are drawing your source image just slightly bigger than it's actual size in screen pixels. So there are some boundaries where extra pixels have to be filled in to make it fill its full on-screen size. Here are some ways to fix this.
Use linear filtering. For the best appearance, use MipMapLinearLinear for the min filter. This is a quick and dirty fix. The results might look slightly blurry.
Draw your game to a FrameBuffer that is sized to the same aspect ratio as you screen, but shrunk down to a size where your sprites will be drawn pixel perfect to their original scale. Then draw that FrameBuffer to the screen using an upsampling shader. There are some good ones you can find by searching for pixel upscale shaders.
The best looking option is to write a custom Viewport class that sizes your world width and height such that you will be always be drawing the sprites pixel perfect or at a whole number multiple. The downside here is that your world size will be inconsistent across devices. Some devices will see more of the scene at once. I've used this method in a game where the player is always traveling in the same direction, so I position the camera to show the same amount of space in front of the character regardless of world size, which keeps it fair.
Edit:
I looked up my code where I did option 3. As a shortcut, rather than writing a custom Viewport class, I used a StretchViewport, and simply changed its world width and height right before updating it in the game's resize() method. Like this:
int pixelScale = Math.min(
height / MIN_WORLD_HEIGHT,
width / MIN_WORLD_WIDTH);
int worldWidth = width / pixelScale;
int worldHeight = height / pixelScale;
stretchViewport.setWorldWidth(worldWidth);
stretchViewport.setWorldHeight(worldHeight);
stretchViewport.update(width, height, true);
Now you may still have rounding artifacts if your pixel scale becomes something that isn't cleanly divisible for both the screen width and height. You might want to do a bit more in your calculations, like round pixelScale off to the nearest common integer factor between screen width and height. The tricky part is picking a value that won't result in a huge variation in amounts of "zoom" between different phone dimensions, but you can quickly test this by experimenting with resizing a desktop window.
In my case, I merged options 2 and 3. I rounded worldWidth and worldHeight up to the nearest even number and used that size for my FrameBuffer. Then I draw the FrameBuffer to the screen at just the right size to crop off any extra from the rounding. This eliminates the possibility of variations in common factors. Quite a bit more complicated, though. Maybe someday I'll clean up that code and publish it.