! Scatter Method

! library "TB Library:PictLib*"

clear

let d = .08

if y$ = "y" then
    ! call Copy_printer(1)
    set window -d, 1+d,  -d, 1+d
  else
    set window -d, 1+d,  -d, 1+d
  end if

option angle degrees
let a=-1
let b=3
let c=-1
let gold = (-b+SQR(b^2-4*a*c))/(2*a)

call setMacPallette

! Grey background (60% white)
let bgr = 3
let bgg = 3
let bgb = 3
call setrgb( bgr, bgg, bgb )
plot area: 0, 0;  0, 1;  1, 1;  1, 0

for w = 0 to 15
    let a = 180 * 1/15 * w + 45
    ! let a = 180 * gold * w
    let dx = d * .8 * cos(a)
    let dy = d * .8 * sin(a)
    let ex = dx / 3
    let ey = dy / 3
    let fx = ex / 3
    let fy = ey / 3
    for r = max( 0, w - 10 ) to min( w, 5 )
        let cy = w - r
        for g = max( 0, cy - 5 ) to min( cy, 5 )
            let b = cy - g
            call setrgb( r, g, b )
            let x = g/5 * .8  +  b/5 * .2
            let y = r/5 * .7  +  b/5 * .3
            plot area: x+dx-ey,y+dy+ex;x+dx+ey,y+dy-ex;x-dx+fy,y-dy-fx;x-dx-fy,y-dy+fx
            if r=0 or r=5 then let redge = 1  else  let redge = 0
            if g=0 or g=5 then let gedge = 1  else  let gedge = 0
            if b=0 or b=5 then let bedge = 1  else  let bedge = 0
            if r = g  and  g = b  then
                if g > 2  then  call setrgb( 2, 2, 2 )  else  call setrgb( 3, 3, 3 )
                ! call setrgb( r + 2*sgn(2.5-r), g + 2*sgn(2.5-g), b + 2*sgn(2.5-b) )
                let doborder = 1
               else  if redge + gedge + bedge = 3  then
                call setrgb( 0, 0, 0 )
                let doborder = 1
               else
                let doborder = 0
               end if
            if doborder = 1  then
                plot x+dx-ey,y+dy+ex; x+dx+ey,y+dy-ex; x-dx+fy,y-dy-fx;
                plot x-dx-fy,y-dy+fx; x+dx-ey,y+dy+ex
               end if
          next g
      next r
  next w


if y$ = "y" then
    ! call Copy_done
    end if

end


sub setrgb( r, g, b )
    if r=0 and g=0 and b=0 then
        set color 255
      else 
        set color 36 * (5-r) + 6 * (5-g) + (5-b)
      end if
  end sub

sub setMacPallette
   for r = 0 to 5
      for g = 0 to 5
         for b = 0 to 5
            if r=0 and g=0 and b=0 then
               set color mix(255) r/5, g/5, b/5
              else 
               set color mix(36*(5-r)+6*(5-g)+(5-b)) r/5, g/5, b/5
              end if
           next b
        next g
     next r
  end sub