Simple and accurate LOS function for BlitzMax

From RogueBasin
Revision as of 20:23, 12 June 2008 by Gbox (Talk | contribs)

Jump to: navigation, search

Simple and accurate LOS function

By Gbox

This fuction assumes you have Type (Or struct) For each map cell And your map
is an array of this Type.
	Type tMapcell
		Field InLos		'// This flag is set true if the player can see the cell.
		Field HasSeen		'// This Flag is when the player has already seen this cell before. 
		Field BlockVision	'// This flag is set for things like walls and doors, otherwise its false.
	End Type

	Global Map:tMapCell[MAPWIDTH,MAPHEIGHT]	'// the map

For this code example we'll assume a Type called tMonster. Monsters in the dungeon are of this type and so is the player.
	Type tMonster
		Field X
		Field Y
		Field Vision		'// this is how many tiles can be seen in any direction from center
	End Type

This Method is Not the fastest, but it's easy To implement And work very well. I dont detect  any kind of performance decrease when using this function.
It works by drawing a filled circle 360 deg around the player And marking map cells that are in LOS.
There are more than 360 Steps in the circle because just using 360 would Create gaps in the vision at a distance.
the fractional amount gives better resolution. [0.1 causes LOS To sometimes seep though doors, >= 0.2 creates gaps. 0.18 seems the sweet spot.
The Code is in BLitzMax (a derivitive of Basic made For games. []) but should be easy To translate.
Function UpdateLOS( m:tMonster )
	If m = Null Then RuntimeError("Null in LOScheck!")
	Local XX:Int, YY:Int
	'// Loop through the entire map resetting the LOS flag
	For xx = 0 To MAPWIDTH - 1
		For yy = 0 To MAPHEIGHT - 1
			If Map[xx, yy].InLOS = True Then
				Map[xx, yy].HasSeen = True	'// Mark the cell as previously seen [drawn in dark colors]
				Map[xx, yy].InLOS = False

	For Local angle:Float = 1 To 360 Step 0.18
		Local dist:Int = 0
		Local x:Float = Float(m.X) + 0.5		'// Add 0.5 to simulate looking from the center of the tile.
		Local y:Float = Float(m.y) + 0.5
		Local xmove:Float = Cos(angle)
		Local ymove:Float = Sin(angle)
			x = x + xmove
			y = y + ymove
			dist = dist + 1
			If dist >= m.Vision Then Exit
			If X >= MAPWIDTH Then Exit
			If y >= MAPHEIGHT Then Exit
			If x < 0 Then Exit
			If y < 0 Then Exit
			Map[x, y].InLOS = True
			If Map[x, y].BlockVision Then Exit
End Function
Personal tools