Implement player:get_point_dir() and player:get_point_screen_pos()

[grorp]

This PR implements player:get_point_dir() as described in #15562

More design decision explanation in addition to the issue:

• I chose yaw/pitch for the internal representation / for the network protocol because this means we only need two floats, a normal vector would need three and a quaternion four

• After a discussion with Warr1024, I've also added player:get_point_screen_pos() so that games can place HUD elements taking the pointer position into account.

  • The value could be derived from point direction (or the other way around) on the server if you reconstructed the client's projection matrix, but this would be hacky and brittle, so I'm instead sending both values from client to server.

To do

This PR is a Ready for Review.

I'm no expert in this rotation business, but the rotation stuff works and makes sense as far as I can tell. EDIT: The more complicated rotation stuff I was doing in the first version of this PR doesn't exist anymore.

How to test

Some quick example code for testing player:get_point_screen_pos()

local hud_ids = {}

core.register_globalstep(function()
	for _, player in ipairs(core.get_connected_players()) do
		player:hud_set_flags({ crosshair = false })
		if not hud_ids[player] then
			hud_ids[player] = player:hud_add({
				type = "image",
				position = player:get_point_screen_pos(),
				alignment = {x = 0, y = 0},
				text = "crosshair.png",
				scale = {x = 1, y = 1},
			})
		else
			player:hud_change(hud_ids[player], "position", player:get_point_screen_pos())
		end
	end
end)

core.register_on_leaveplayer(function(player)
	hud_ids[player] = nil
end)

Install GGraffiti with a patch to use player:get_point_dir(): grorp/ggraffiti@1eed15c

1. The mod must work as usual on desktop
2. The mod must work as usual on Android with touch_use_crosshair = true
3. The mod must now work properly on Android with touch_use_crosshair = false: You will now paint where you put your finger
   • arguably the camera shouldn't move while painting, but that's a different UX improvement

Also verify that things still work correctly with non-zero eye offset (player:set_eye_offset)

[nauta-turbidus]

I'm only now realizing how useful this would be for mobile compatibility.

Think hitting enemies with a weapon that is supposed to depend on distance in some way. You have no reliable way to detect the distance currently, because simple position difference length doesn't account for collision boxes for example.

This would allow to at least do a raycast along the actual strike direction (because doing it along look direction would break mobile compatibility), find intersection position, and get distance as position difference length from that to player "eyes".

[Zughy]

I've also added player:get_point_screen_pos() so that games can place HUD elements taking the pointer position into account.

Practical example?

[nauta-turbidus]

I've also added player:get_point_screen_pos() so that games can place HUD elements taking the pointer position into account.

Practical example?

Some movable crosshair?

[grorp]

I've also added player:get_point_screen_pos() so that games can place HUD elements taking the pointer position into account.

Practical example?

A crosshair-like HUD or a "what am I looking at" HUD text like the one in NodeCore (currently that one is placed next to the crosshair afaik, once it takes the actual pointing direction into account, it should also be placed next to the actual pointer position).