Quick answer: Render to a fixed virtual resolution and scale it to the window with integer (nearest) scaling, letterboxing the remainder, so pixels stay square at every window size.
A pixel-art game looks crisp at one resolution and smeared at another because it scales non-integer. Render at a fixed base resolution and upscale by whole numbers.
How to fix it
1. Use a fixed base resolution
Render the game at a constant virtual resolution and scale the result to the window, instead of rendering directly at the variable window size.
2. Scale by integer factors
Upscale with nearest-neighbor at whole-number factors (2x, 3x) so the pixel grid stays uniform; letterbox or pillarbox the leftover space.
3. Set the texture filter
Use nearest filtering on sprites and the viewport so the integer scale does not get blurred by bilinear filtering on the final blit.
Catching the ones you can't reproduce
The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.
Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.
This is where a tool like Bugnet earns its place. Its SDK captures every Godot error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.
Ship the fix, watch the signature disappear from the next build. That's how you know it's really gone.