option explicit
option default integer
dim polyx(3)=(100,300,250,75)
dim polyy(3)=(50,75,300,250)
dim count=4,ystart=50,yend=300
line polyx(0),polyy(0),polyx(1),polyy(1)
line polyx(1),polyy(1),polyx(2),polyy(2)
line polyx(2),polyy(2),polyx(3),polyy(3)
line polyx(3),polyy(3),polyx(0),polyy(0)
' load some sort of image to copy into the quadrilateral
' load jpg "amigapics/bigtut",400,0

fillint(4,ystart,yend)
do:loop
sub fillint(count, ystart,  yend)

   local FLOAT nodeX(count)
   local nodes, y, i, j, k
   local float temp
   local f=rgb(red)
   local c=rgb(green)
   local xstart, xend

   for y = ystart to yend-1

       nodes = 0
       j = count-1
       for i = 0 to count-1
           if (polyY(i) <  y and polyY(j) >= y) or (polyY(j)<y and polyY(i) >= y) then
               nodeX(nodes) = (polyX(i) + (y - polyY(i)) / (polyY(j) - polyY(i)) * (polyX(j) - polyX(i)))
             nodes=nodes+1
           endif
           j = i
       next i

       for i = 1 to nodes-1
           temp = nodeX(i)
           for j = i to 1 step -1
               if temp >= nodeX(j-1) then exit for
               nodeX(j) = nodeX(j-1)
           next j
           nodeX(j) = temp
       next i

       for i = 0 to nodes-1 step 2
        xstart=int(nodeX(i))+1
        xend=int(nodeX(i+0.999999999))-1
        for k=xstart to xend
          pixel k,y,f 'replace this with lookup into a rectangle
        next k
      next i
   next y
end sub