Chasing but limiting the turning angle

BlitzMax Forums/BlitzMax Beginners Area/Chasing but limiting the turning angle

Ryan Burnside

(Posted 2007) [#1]

I've written a simple chasing behavior for my enemie objects. Basically the player may change direction in incriments of three degrees so i can't just tell the enemies to face and move towards the player. What I've tried to do is make the enemy find the angle to the target x and y (tx,ty) and choose weither to add or subtrack three degrees from the current direction. It seems that when the direction to the player is 0, the eneies start weaving toward the left and ignore the direction to the player.

I need to find if direction-3 is closer than direction+3 to the target direction then choose the right action.

Method chase(tx#,ty#)
' since the chaser can omly change direction in incriments of three
' find which direction is closer to the target angle direction+3 or direction-3


	If direction-point_direction(x,y,tx,ty)<0
		direction:+3
	End If
	If direction-point_direction(x,y,tx,ty)>0
		direction:-3
	End If
	

	x:+Cos(direction)*speed
	y:+Sin(direction)*speed
End Method

I've made a small file that you can compile to see:

' lets make some chasing missles
Strict
Graphics 640,480
Function point_direction#(x1#,y1#,x2#,y2#)
Local direction#= ATan2(y1-y2,x1-x2)+180

	
Plot 320,240
Return direction

EndFunction
Type missle
	Field x#,y#,direction#,speed#
	Global missle_list:TList = New TList
	
	Function create (x#,y#,direction#,speed#)
	Local temp:missle = New missle
	temp.x=x
	temp.y=y
	temp.direction = direction
	temp.speed = 5
	ListAddLast(missle_list,temp)
	End Function
	Method update()
	Local target_x#=MouseX()
	Local target_y=MouseY()
	Local max_angle#=3
	Local target_direction#=point_direction(x,y,target_x,target_y)
	
	If direction< target_direction
		direction:+max_angle
	EndIf
	
	If direction>target_direction
		direction:-max_angle
	EndIf
	
	
	
	x:+Cos(direction)*speed
	y:+Sin(direction)*speed
	DrawOval(x-5,y-5,10,10)
	End Method
End Type




	missle.create(Rand(640),Rand(480),0,3)

While Not KeyDown (KEY_ESCAPE)
	
	For Local i:missle = EachIn(missle.missle_list)
		i.update()
	Next
	DrawText(point_direction(320,240,MouseX(),MouseY()),12,12)
	Flip
Wend

DIJ	(Posted 2007) [#2]

If direction-point_direction(x,y,tx,ty)<0
direction:+3
End If
If direction-point_direction(x,y,tx,ty)>0
direction:-3
End If

You are checking for greater than 0 or less than 0, never 0.

try this function, I've used it and it works fine

Function RotateToPoint(originalAngle:Int,targetAngle:Int,turnspeed:Float)

Local angleDiff
angleDiff = originalAngle - targetAngle
	If angleDiff < 0 Then angleDiff = 360 + angleDiff
	If angleDiff > 359 Then angleDiff = 360 - angleDiff
	
	If angleDiff > 180 Then Return turnspeed
	If angleDiff < 181 Then Return -turnspeed

End Function

Just pass your original angle, target angle and how fast you want them to turn and it returns the angle change required.

Ryan Burnside

(Posted 2007) [#3]

Thanks a million . :)