An odd new issue. The coordinates I’m getting from action.x and action.y are offset by half a pixel. +0.5 X and -0.5 Y.
Defold 1.2.183, Linux Mint 20.1 Ulyssa.
Reported on github: action.x and action.y are offset by half a pixel. · Issue #5925 · defold/defold · GitHub
Can someone else test this project to see if they get the same results? (without resizing the window of course.)
mouse-pos-test.zip (2.7 KB)
Not only that, but also this:
And these are not new issues, this has been the case from the very beginning.
Thank you for reporting and reminding us of these. The upside now is that the source code is available and accepting pull requests! 
Thanks! I guess with a high-dpi screen the coordinates are halved, right?
If you double that gui pos, you get: 409.5, 638.5
Which is exactly the +0.5 X and -0.5 Y from screen pos that I have.
It’s really mind-boggling that I haven’t noticed this before. I thought I’d done the conversion between them dozens of times. I guess I usually only use screen coordinates outside of GUI because they don’t get stretched.
So, I tried looking at the source code to figure this out and this is what I found:
The 0.5 offset seems very intentional. I would like to see the reason of that explained, though I assume it’s to make a pixel coordinate centered.
The y coordinates being in [1, window_height] and not in [0, window_height - 1] as expected is likely due to off-by-one error in this line:
So, the simplest fix is
input_action.m_ScreenY = window_height - 1 - action->m_Y;
Keep in mind though, that this is my first time looking at Defold source code, so I may be completely wrong 
I also don’t have the knowledge to build and test the engine, so I can’t confirm the proposed fix actually works.
Correct. According to the very old commit it was due to picking:
You’re right. That’s probably it.