Add hybrid hold-toggle aiming for better accessibility

Clicking the aim button will now toggle aiming instead of requiring
the user to hold down the aim button. However, if the aim button
is held for more than 0.4 seconds, aiming will be released once the
user releases the aim button.

This provides better accessibility for trackpad users while still
supporting the old way of aiming.

player/player.gd

@@ -7,6 +7,11 @@ const CAMERA_CONTROLLER_ROTATION_SPEED = 3.0
 const CAMERA_X_ROT_MIN = -89.9
 const CAMERA_X_ROT_MAX = 70
 
+# Release aiming if the mouse/gamepad button was held for longer than 0.4 seconds.
+# This works well for trackpads and is more accessible by not making long presses a requirement.
+# If the aiming button was held for less than 0.4 seconds, keep aiming until the aiming button is pressed again.
+const AIM_HOLD_THRESHOLD = 0.4
+
 const DIRECTION_INTERPOLATE_SPEED = 1
 const MOTION_INTERPOLATE_SPEED = 10
 const ROTATION_INTERPOLATE_SPEED = 10
@@ -22,6 +27,13 @@ var motion = Vector2()
 var velocity = Vector3()
 
 var aiming = false
+
+# If `true`, the aim button was toggled on by a short press (instead of being held down).
+var toggled_aim = false
+
+# The duration the aiming button was held for (in seconds).
+var aiming_timer = 0.0
+
 var camera_x_rot = 0.0
 
 onready var initial_position = transform.origin
@@ -89,7 +101,21 @@ func _physics_process(delta):
 	camera_x.y = 0
 	camera_x = camera_x.normalized()
 
-	var current_aim = Input.is_action_pressed("aim")
+	var current_aim = false
+
+	# Keep aiming if the mouse wasn't held for long enough.
+	if Input.is_action_just_released("aim") and aiming_timer <= AIM_HOLD_THRESHOLD:
+		current_aim = true
+		toggled_aim = true
+	else:
+		current_aim = toggled_aim or Input.is_action_pressed("aim")
+		if Input.is_action_just_pressed("aim"):
+			toggled_aim = false
+
+	if current_aim:
+		aiming_timer += delta
+	else:
+		aiming_timer = 0.0
 
 	if aiming != current_aim:
 		aiming = current_aim