Add a test that covers input/actions/movement controls and checks the output is correct.

Perhaps we can manually call the update function:

And mock out ebiten.IsKeyPressed?

This would have really helped with edge cases in #9

If a non-meta key is held down, repeat it after a time delay.

Default to a delay of 500ms, then the held down key is repeated every 30ms thereafter.

Hey, I read your blog post on the editor, as Hajime Hoshi shared it on the discord chat. I follow the development of Ebitengine fairly closely, and I wanted to share a few tips and ideas that you may find useful / interesting, even if you are unlikely to implement most of them. Using an issue for this feels a bit wrong, but you can just close it without remorse, no problem, this is only meant to be informative for you or other people that may want to do something similar or take things one step further.

• Proper font rendering requires proper layout: you need to take into account the display DPI if you want to do any kind of sharp text rendering. This can be done by taking ebiten.DeviceScaleFactor() into account and applying it on the Layout() function. While many Ebitengine examples do this, you can also check this article that goes more in depth explaining it. It also touches on LayoutF, which can be fairly important for an application such as a text editor.
• Pixel fonts are tricky: even if you are using high DPI, making pixel fonts look sharp can still be hard. In particular, the standard font DPI used is 72, but CSS uses 96 instead. For this reason, many fonts are designed with that in mind, and certain point sizes are likely to look better or worse. There are two tricks to solve this: either try both 72 and 96 DPIs when creating a font face to see what looks best, or apply a 3/4 or 4/3 factor (never remember which one of the two) when computing the font size.
• Efficient GPU usage: since Ebitengine v2.5.0 (still in alpha), draw calls are optimized when no draw commands happen. This means you can use ebiten.SetScreenClearedEveryFrame(false) and avoid doing anything in the Draw() function unless necessary. This will make a massive difference in power usage, and for an application that's idle most of the time, this is a very big deal. It's still not as efficient as regular GUI frameworks, which skip buffer swaps altogether and often don't have a fixed timestep update loop called regularly, but it's still a massive improvement.

Maybe changing to vectorial fonts now is too bothersome, and you are probably doing this only for fun and learning, but wanted to share anyway! Have fun with Ebitengine!

Editor.Layout() should return the logical size of the editor, no just echoing back the screen size.

• PageUp/PageDown should move by page.
• Cursor down at bottom of visible page should scroll up by single line, not page.
• Cursor up at top of visible page should scroll down by single line, not page.
• Home should go to beginning of line.
• End should go to end of line.

I'm interested in contributing an adaptation of your editor, to make it a library that can be more easily pulled into another Ebitengine application.

Can you add a license to this code, so that it's clearer in how it can be used?

I prefer MIT and BSD-3 Clause myself, as Go is a statically linked language that doesn't play well with mixing in GPL libraries, but of course it's up to you.