10 rem Converge on a value demo
15 rem Testing a routine that will smoothly converge on a value, easing into a stop
20 rem by Golden Child
100 hgr
110 c=0:d=100 :gosub 5000 : ct=0
120 co=3:x1=c:y1=0:x2=cl:y2=50:gosub 5100:x1=c2:y1=100:gosub 5100:gosub 5500 :c2=cl::c2=cl:cl=c:gosub 9000
125 if abs(c-d)<.1 then ? "DIST="di" FRAMES="ct:d=rnd(1)*279 : ct=0 : di=d-c:?d,c,di
130 ct=ct+1:goto 120

9000 rem converge   c=cur value, d=desired value, mr=max rate, md=max dist, ch=change, cd=dist to go
9010 mr=10:md=100
9020 cd=d-c
9030 if cd>md then cd=md
9040 if abs(cd)<0.1 then c=d
9045 ch = cd/md*mr
9050 c=c+ch: rem ?"c="c" d="d" ch="ch" ct="ct
9051 if abs(ch)<0.1 then c=d
9060 return

5000 rem init display list   :  rem SC = screen to draw
5001 dim dl(2,100,5):hgr2:hgr
5002 SC=0 : DL(0,0,0)=0 : DL(1,0,0)=0  :gosub 5500: rem DL(X,0,0) = NUM OF POINTS
5003 return

5100 rem draw line on other screen
5110 poke 230,(SC+1) * 32  : rem forgot the +1 part
5111 if not(x1>=0 and x1 <=279 and x2 >=0 and x2<=279 and y1>=0 and y1 <=159 and y2>=0 and y2<=159) then return
5120 rem bug should be DL SP = DL(SC,0,0) + 1 : SL(SC,0,0)=SP : ? sp
5120 SP = DL(SC,0,0) + 1 : DL(SC,0,0)=SP : rem  ? sp
5130 DL(SC,SP,0)=CO
5131 DL(SC,SP,1)=X1
5132 DL(SC,SP,2)=Y1
5133 DL(SC,SP,3)=X2
5134 DL(SC,SP,4)=Y2
5140 HCOLOR=CO : HPLOT X1,Y1 TO X2,Y2
5190 RETURN

5400 rem erase lines
5410 for SP = 1 TO DL(SC,0,0) : HCOLOR=0 : rem ? "erase" sc ,sp
5411 HPLOT DL(SC,SP,1),DL(SC,SP,2) TO DL(SC,SP,3),DL(SC,SP,4) : NEXT
5412 DL(SC,0,0)=0  : rem clear the list after erasing
5420 RETURN

5500 rem swap screens
5510 SC = NOT SC
5511 POKE 49236+(NOT SC),0   : rem select page that we're drawing to
5514 rem ? "SC="sc
5515 poke 230,32*(sc+1):gosub 5400  : rem forgot to switch the drawing page
5520 RETURN