Line of sight

[slenkar]

To see if 2 game characters can see each other you need 2 functions

distance:

Code:

Function distance (x1 as Integer, y1 as Integer, x2 as Integer, y2 as Integer) as Integer Dim x as Integer x=ABS(x1-x2) Dim y as Integer y=ABS(y1-y2) Return Sqr((x^2)+(y^2)) End Function

line:

Code:

Function line(X1 as Integer,Y1 as Integer,X2 as Integer,Y2 as Integer) as Integer 'creates a line of individual co-ords from X1,Y1 to X2,Y2 at any angle Dim dist as Integer dist=distance(X1,Y1,X2,Y2) dim bresiter as Integer For bresiter=0 To dist bresx(bresiter)=0 bresy(bresiter)=0 Next Dim steep as Integer if Abs(Y2-Y1) > Abs(X2-X1) then steep=1 else steep=0 end if PRINT AT 1,0 ; PAPER 1 ; INK 0 ; "steep "+STR(steep) If steep =1 Then Dim Temp as Integer Temp=X1 X1=Y1 Y1=Temp Temp=X2 X2=Y2 Y2=Temp End If Dim DeltaX as Integer DeltaX=Abs(X2-X1) Dim DeltaY as Integer DeltaY=Abs(Y2-Y1) Dim IError as Integer IError=0 Dim DeltaError as Integer DeltaError=DeltaY Dim x as Integer x=X1 'Start at X1,Y1 Dim y as Integer y=Y1 Dim XStep as Integer Dim YStep as Integer If X1<X2 Then XStep=1 Else XStep=-1 end if If Y1<Y2 Then YStep=1 Else YStep=-1 'Direction end if Dim iter as Integer iter=1 While x<>X2 x=x+XStep 'Move in X IError=IError+DeltaError 'Add to counter If (IError SHL 1)>DeltaX then 'Would it overflow? y=y+YStep 'Move in Y IError=IError-DeltaX 'Overflow/wrap the counter End if If steep then bresx(iter)=y bresy(iter)=x Else bresx(iter)=x bresy(iter)=y End If iter=iter+1 If iter>dist then 'Print at 3,0;PAPER 1;INK 0;"bresenham over distance "+STR(dist) Return dist End If Wend Return dist End Function

create 2 arrays to hold the x and y coordinates of the line

Code:

Dim bresx(350) as Integer Dim bresy(350) as Integer

The size of the arrays should be the distance of the longest line you intend to create
a line going across the screen of the speccy is about 322 in length

You have 2 characters on a playing field that has x and y coordinates

you call the line function:
one character is at 1,1
the other is at 100,95

Code:

Dim dist as Integer dist=line(1,1,100,95)

then finally you go through the co-ordinates on the line to check if anything is in the way, like walls or other characters

Code:

Dim can_see:UByte can_see=1 for x=0 to dist if wall_in_way(bresx(x),bresy(x)) then can_see=0 end if next if can_see =1 then 'yes they can see each other end if if can_see =0 then 'no they can not see each other end if