Don't print warning messages for DisplayServer functions in headless mode

[Calinou]

DisplayServer methods that only have a cosmetic effect print a warning (instead of an error). These warnings can be silenced in headless mode, as it's assumed that the cosmetic effect is undesired in headless mode anyway (e.g. changing mouse cursor shape).

This prevents spurious warnings from appearing when running the editor in headless mode, e.g. on CI to export a project.

Methods that print an error will continue to do so, as their returned value may not match expectations and have cascading consequences on the project (e.g. clipboard data not being retrievable).

• See Supressing mouse warnings from running server in –headless mode - Godot Forum.

Testing project: test_headless_methods.zip
Run with and without --headless from a terminal and compare output.

Preview

Before

$ godot --headless 
Godot Engine v4.3.dev.custom_build.b091162a9 (2024-04-10 15:49:59 UTC) - https://godotengine.org

WARNING: Custom cursor shape not supported by this display server.
     at: cursor_set_custom_image (servers/display_server.cpp:636)
WARNING: Clipboard is not supported by this display server.
     at: clipboard_set (servers/display_server.cpp:506)
ERROR: Clipboard is not supported by this display server.
   at: clipboard_get (servers/display_server.cpp:510)

ERROR: Virtual keyboard not supported by this display server.
   at: virtual_keyboard_get_height (servers/display_server.cpp:624)
0
WARNING: Native dialogs not supported by this display server.
     at: dialog_input_text (servers/display_server.cpp:652)

After

$ godot --headless
Godot Engine v4.3.dev.custom_build.67b915f63 (2024-04-11 21:14:41 UTC) - https://godotengine.org

ERROR: Clipboard is not supported by this display server.
   at: clipboard_get (servers/display_server.cpp:517)

ERROR: Virtual keyboard not supported by this display server.
   at: virtual_keyboard_get_height (servers/display_server.cpp:631)
0

Non-headless output for comparison

This is left unchanged in this PR.

$ godot           
Godot Engine v4.3.dev.custom_build.67b915f63 (2024-04-11 21:14:41 UTC) - https://godotengine.org
Vulkan 1.3.277 - Forward+ - Using Device #0: NVIDIA - NVIDIA GeForce RTX 4090

test
ERROR: Virtual keyboard not supported by this display server.
   at: virtual_keyboard_get_height (servers/display_server.cpp:631)
0
WARNING: Native dialogs not supported by this display server.
     at: dialog_input_text (servers/display_server.cpp:663)

[Riteo]

Sorry, wouldn't it be simpler to just implement a stub method stub methods in the headless class? Since it's an exception, I think that a local solution would be better.

Edit: oops I said "stub method" but I meant like, stubs in general.

[m4gr3d]

Sorry, wouldn't it be simpler to just implement a stub method stub methods in the headless class? Since it's an exception, I think that a local solution would be better.

Edit: oops I said "stub method" but I meant like, stubs in general.

I agree; this breaks encapsulation principle if the parent / base class has special logic for one of its derived class.

[m4gr3d]

Added feedback in comments.

[Calinou]

Sorry, wouldn't it be simpler to just implement a stub method stub methods in the headless class? Since it's an exception, I think that a local solution would be better.

Edit: oops I said "stub method" but I meant like, stubs in general.

Done. I've tested the MRP again and I get the same output as before (in both headless and non-headless mode).

[aaronfranke]

This isn't my area and I haven't tested it but the change is very straightforward and looks good to me.

[akien-mga]

I'm not against adding stubs, but at least some of those may need to be guarded with DisplayServer::get_singleton()->has_feature() checks before being called (which means that actually showing a warning when called should be kept, as it's information for end users when they themselves wrongly rely on the API).

So it might be worth reviewing places in the engine that call some of those APIs without guarding with the proper feature check.

For example:

WARNING: Custom cursor shape not supported by this display server.
     at: cursor_set_custom_image (servers/display_server.cpp:636)

Shouldn't happen anymore already after e6d0bf3.

DisplayServerHeadless::has_feature() is always false so in theory it should be sufficient.

[akien-mga]

If someone wants to look into which checks may actually be missing in the core engine before merging this (see my above comment), that could be good.

But otherwise I'm also fine merging this as is if there's no objection from @bruvzg on making these no-ops (so end users won't know why they don't work on platforms that don't support them, and we need to make sure the docs flag those properly).

[bruvzg]

Adding stubs to the headless DS should be fine.

[akien-mga]

Thanks!