Raster drawn road race

[Rod]

If you have any time over the holidays help me sort this out. You can get the tutorial here www.extentofthejam.com/pseudo/

I open this old project up every year and every year so far I have failed. It is a classic raster drawn road, it recedes into the distance and should curve gracefully towards you as you drive into the curves. Its the curves I can't get right. The straight road and banding work, Cundo showed us a curve last year but I need eventually to have flowing curves, straights and hills. But lets get the curves right first.


The idea is that there is a "segment" of road that may be curved or straight and as you move forwards it falls down the screen towards you. You should always be in the middle of the road and the change of "segment" should fall down the screen towards you moving seamlessly from curve to straight or curve to curve. Mine kinda jump about and surprise me. Not good.




   'nomainwin

   rasterlines = 260   'how many raster lines make up the road
   speed = 10          'speed in raster lines
   cameray = -100      'arbitrary camera height
   width = 800         'screen width
   height = 600        'screen height
   rasterplayer = 10   'player sprite's raster line
   midx = 400          'middle of the road

   'precalculate the 3d distance each rasterline represents
   'this is for the banded shading
   'note that we end up drawing 260 rasterlines because
   'the road becomes too small to draw after that
   'also store the flat road width at any point in the distance
   dw=(800-10)/rasterlines
   w=800
   dim zmap(rasterlines,2)
   for raster=1 to rasterlines
       zmap(raster,1) = cameray / (raster - (height / 2))
       zmap(raster,2) = w/2
       w=w-dw
       'print raster,zmap(raster,1),zmap(raster,2)
   next

   'normalise the 3d distance value so that player sprite line is 100%
   'we are not there yet but we will have a player sprite
   b = 1 / zmap(rasterplayer,1)
   b = b * 100
   for raster=1 to rasterlines
       'print raster,zmap(raster,1),
       zmap(raster,1)=zmap(raster,1)*b
       'print zmap(raster,1)
   next


   WindowWidth = 800 : WindowHeight = 660
   UpperLeftX = INT((DisplayWidth-WindowWidth)/2)
   UpperLeftY = INT((DisplayHeight-WindowHeight)/2)
   Open "Road Race" for graphics_nsb_nf as #main
   #main "trapclose [quit]"
   #main "down;fill white;flush"

   'we only need to draw the whole sky once
   #main "fill blue"


   texturepos = 0
   segmentpos = rasterlines

   DX = 0
   DDX = 0


   [draw]
   scan
       'set everything to mid, bottom of screen no curve
       DX = 0
       X= midx
       screenpos = height-1

       FOR raster = 1 TO rasterlines
           'decide if we need to draw a light or a dark line
           IF (zmap(raster,1) + texturepos) MOD 100 > 50 THEN
               GrassColor$ = "green"
               RoadColor$ = "darkgray"
           ELSE
               GrassColor$ = "darkgreen"
               RoadColor$ = "lightgray"
           END IF
           'get the width of the road at this distance
           roadw=(zmap(raster,2))

           'draw the grass then the road on top
           #main "color ";GrassColor$
           #main "line ";0 ;" ";screenpos;" ";width;" ";screenpos
           #main "color ";RoadColor$
           #main "line ";X - roadw;" ";screenpos;" ";X + roadw;" ";screenpos
           screenpos=screenpos - 1

           if raster<segmentpos then DDX=DDXX
           DX=DX+DDX
           X=X+DX
       next

       'advance the texture position so that the banding scrolls
       texturepos = texturepos + speed
       if texturepos>100 then texturepos=texturepos-100

       'drop the segment (curve) down the screen
       segmentpos = segmentpos - speed
       'choose a new segment right left curved or straight
       if segmentpos<0 then
           segmentpos = segmentpos + rasterlines
           segment=rnd(0)
           if segment>.6 then DDXX=.01
           if segment<.3 then DDXX=-.01
           if segment >.3 and segment<.6 then DDXX=0
       end if




goto [draw]


[quit]
timer 0
close #main : end