refactor: fastport tg beam datums

code/__DEFINES/beam.dm

@@ -0,0 +1,12 @@
+/// Called before beam is redrawn
+#define COMSIG_BEAM_BEFORE_DRAW "beam_before_draw"
+	#define BEAM_CANCEL_DRAW (1 << 0)
+
+/// Sent to a beam when an atom enters any turf the beam covers: (obj/effect/ebeam/hit_beam, atom/movable/entered)
+#define COMSIG_BEAM_ENTERED "beam_entered"
+
+/// Sent to a beam when an atom exits any turf the beam covers: (obj/effect/ebeam/hit_beam, atom/movable/exited)
+#define COMSIG_BEAM_EXITED "beam_exited"
+
+/// Sent to a beam when any turf the beam covers changes: (list/datum/callback/post_change_callbacks)
+#define COMSIG_BEAM_TURFS_CHANGED "beam_turfs_changed"

code/__HELPERS/maths.dm

@@ -250,3 +250,15 @@
 			return "centuple"
 		else //It gets too tedious to use latin prefixes from here.
 			return "[number]-tuple"
+
+/// Angle between two arbitrary points and horizontal line same as [/proc/get_angle]
+/proc/get_angle_raw(start_x, start_y, start_pixel_x, start_pixel_y, end_x, end_y, end_pixel_x, end_pixel_y)
+	var/dy = (32 * end_y + end_pixel_y) - (32 * start_y + start_pixel_y)
+	var/dx = (32 * end_x + end_pixel_x) - (32 * start_x + start_pixel_x)
+	if(!dy)
+		return (dx >= 0) ? 90 : 270
+	. = arctan(dx/dy)
+	if(dy < 0)
+		. += 180
+	else if(dx < 0)
+		. += 360