Add system-offset options
While currently the existing window handling code is technically correct,
on Android opertating sytem certain devices (or SDL on them) behave weirdly.
In the engine we have two types of coordinates, screen and script:
- Screen coordinates are coordinates the game window runs in (needed
to translate e.g. mouse pointer hover area).
- Script coordinates are coordinates the game runs in (always 1080p).
So, for a 2400x1080 screen, as found in Redmi Note9 Pro in landscape
mode, the following values are set:
- script_width / script_height = 1920 / 1080 (game resolution)
- screen_width / screen_height = 1920 / 1080 (windowed game resolution,
unused in fullscreen really)
- screen_ratio1 / screen_ratio2 = 1080 / 1080 (native screen height
/ game script height)
- fullscript_width / fullscript_height = 2400 / 1080 (screen resolution
in game coordinates)
- fullscreen_width / fullscreen_height = 1920 / 1080 (game resolution
in screen coordinates)
- fullscript_offset_x / fullscript_offset_y = 240 / 0 (offset to game
on device screen in game coordinates)
What we actually observe on the device is padding of 420 pixels to the
left and 210 pixels to the right with the game width cut to 1770 pixels
wide. If fullscript_offset_x becomes 0 on a normal device that would
have meant the game would run in the top left corner, but it is absolutely
not what happens on Redmi Note9 Pro. What we observe after the change is
left padding of 180 pixels and right padding of 300 pixels with the game
width being 1920 as normal. I guess, neither is correct, but the latter
is at least useable.
What we concluded from these values is that on this device the game
always runs at 180 pixel offset to the right (420 - 240 = 180) enforced
by some system software (or maybe SDL). This is horrifying but not much
we can do about it. To handle the issue as such and get a perfectly centred
image fullscript_offset_x should be 60 as calculated from (2400 - 1920)
/ 2 - 180. Here 180 is so called system_offset_x.
This patch introduces such a variable and makes it user-configurable
via engine arguments or ons.cfg.
