simple function to create curved road segments by using triangle objects. You can set radius of turn, angle of turn, width of road, and segments per section (resolution)

by just typing in this:
drawroad(1,xcenter,ycenter,300,400,16,180,prevangle,trianglecount)
would create a 180 degree curved section of road with a width of 10 units (the difference between the inside radius and the outside radius), using 16 segments, each segment is 2 triangles, so 32 triangles total. The more segments, the smoother the turn. 8 segments per 90 degrees seems to work good. You can play with the z values inside the function where the triangles are drawn. They are all set to zero, but it is totally possible to change them and make banked turns or dips and hills.

                                    ` This code was downloaded from The Game Creators
                                    ` It is reproduced here with full permission
                                    ` http://www.thegamecreators.com
                                    
                                    REM Project: Curved Roads Function
REM Created: 3/7/2007 8:15:47 PM
REM Created by Mike Shihrer
REM ***** Main Source File *****
REM

REM demonstrates function to draw curved roads.
REM at this time, turns must alternate between right and left
REM for simplicity sake for me, the z coordinate is actually the height value
REM feel free to use this code, a credit to me would be cool though, thanks


autocam off

rem load your own road texture here, and uncomment out the texture command inside the drawroad function
rem load image "E:\Dev\Projects\STRider\media\road.jpg",1
rem load image "E:\Dev\Projects\STRider\media\road1.jpg",2


REM array stores x,y coords for triangles to be drawn

dim coordinatearray#(4,36)
Global trianglecount rem keeps track of number of triangles
Global xcenter as float rem center of radius of turn x position
Global ycenter as float rem center of radius of turn y position
Global prevangle as float rem the angle of the end of the last curve section
Global lastradius as float rem the outside radius of the last curve section
Global cameraflag as integer


xcenter = 15000 rem pick somewhere way out in space to avoid negative numbers
ycenter = 15000 rem pick somewhere way out in space to avoid negative numbers
prevangle = 180 rem start angle of first turn
trianglecount = 0 rem initialize triangle object numbers here, it increments as you draw more triangles
lastradius = 0 rem should start at zero here


rem parameters are : drawroad(direction 0 for left, 1 for right,x pos of radius center, y pos of radius center, inside radius, outside radius, segments per curve, angle of turn, last turn ending angle, triangle object number)

drawroad(1,xcenter,ycenter,300,400,16,180,prevangle,trianglecount)
drawroad(0,xcenter,ycenter,300,400,8,90,prevangle,trianglecount)
drawroad(1,xcenter,ycenter,1000,1100,2,5,prevangle,trianglecount)
drawroad(0,xcenter,ycenter,200,300,4,90,prevangle,trianglecount)
drawroad(1,xcenter,ycenter,300,400,16,180,prevangle,trianglecount)
drawroad(0,xcenter,ycenter,300,400,8,90,prevangle,trianglecount)
drawroad(1,xcenter,ycenter,1000,1100,2,5,prevangle,trianglecount)
drawroad(0,xcenter,ycenter,200,300,4,90,prevangle,trianglecount)



position camera xcenter,ycenter,-15
xrotate camera -90 rem comment this out for a top down view of the road

Do

movecamera()

Loop


function drawroad(direction as integer,centerx as float, centerY as float, insideradius as float, outsideradius as float, segments as integer, angle as float,lastangle as float,triangles as integer)

xpi as float
ypi as float
xpo as float
ypo as float
a as float
calcangle as float

calcangle = angle / segments

if direction = 0 rem this is for laft turns

rem Calculate radius centerx and centery between turns

xcenter = centerx + (insideradius + lastradius) * cos(prevangle)
ycenter = centery + (insideradius + lastradius) * sin(prevangle)

a = lastangle - 180 rem keep the angle in a clock wise orientation
rem plot the x and y positions on the curves
for b = 1 to (segments + 1)
   xpi = xcenter + insideradius * cos(a)
   ypi = ycenter + insideradius * sin(a)
   xpo = xcenter + outsideradius * cos(a)
   ypo = ycenter + outsideradius * sin(a)

REM store the segment coordinate positions in an array so we can have the positions for the triangles
   coordinatearray#(1,b) = xpi
   coordinatearray#(2,b) = ypi
   coordinatearray#(3,b) = xpo
   coordinatearray#(4,b) = ypo
   a = a + calcangle

next b
   rem update prevangle with ending angle of curve, update lastradius so can calculate next radius centerx and centery
   prevangle = a - calcangle
   lastradius = outsideradius

endif


if direction = 1 rem this is for right turns

xcenter = centerx + (insideradius + lastradius) * cos(prevangle)
ycenter = centery + (insideradius + lastradius) * sin(prevangle)

a = lastangle + 180

for b = 1 to (segments + 1)
   xpi = xcenter + insideradius * cos(a)
   ypi = ycenter + insideradius  * sin(a)
   xpo = xcenter + outsideradius * cos(a)
   ypo = ycenter + outsideradius * sin(a)

REM store the segment coordinate positions in an array so we can have the positions for the triangles
   coordinatearray#(1,b) = xpi
   coordinatearray#(2,b) = ypi
   coordinatearray#(3,b) = xpo
   coordinatearray#(4,b) = ypo
   a = a - calcangle

next b

   prevangle = a + calcangle
   lastradius = outsideradius

endif

rem loop through the coordinatearray and draw the triangles
for i = 1 to segments
   make object triangle triangles + i,coordinatearray#(1,i),coordinatearray#(2,i),0,coordinatearray#(3,i),coordinatearray#(4,i),0,coordinatearray#(3,(i+1)),coordinatearray#(4,(i+1)),0
   rem texture object triangles + i,1

next i

triangles = triangles + i

 for ii = 1 to segments
    make object triangle triangles + ii,coordinatearray#(1,ii),coordinatearray#(2,ii),0,coordinatearray#(3,ii+1),coordinatearray#(4,ii+1),0,coordinatearray#(1,(ii+1)),coordinatearray#(2,(ii+1)),0
    rem texture object triangles + ii,2

 next ii
triangles = triangles + ii
trianglecount = triangles + 1


endfunction
function movecamera()

if upkey() then move camera .50
if downkey() then move camera -.5
if leftkey() then turn camera left .2
if rightkey() then turn camera right .2


endfunction