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#constant SW 256
#constant SH 256

sync on : sync rate 0

dim pal(255)
dim tab(SW, SH)

box 0, 0, 128, 1, 0, 0, 255, 255
box 128, 0, 256, 1, 255, 255, -1, -1

for i = 0 to 255
   pal(i) = point(i, 0)
next i

for x = 0 to SW
   for y = 0 to SH
      tab(x, y) =  2000 / sqrt(x * x + y * y)
   next y
next x
tab(0, 0) = 255

repeat

   x1 = 60 * cos(a)      + 30 * sin (-a)    + SW / 2
   y1 = 30 * cos(-a * 2) + 60 * sin (a)     + SH / 2
   x2 = 30 * cos(a)      + 60 * sin (a * 2) + SW / 2
   y2 = 60 * cos(a)      + 30 * sin (a)     + SH / 2
   x3 = 45 * cos(-a)     + 45 * sin (a)     + SW / 2
   y3 = 45 * cos(a * 2)  + 45 * sin (-a)    + SH / 2

   inc a, 2

   lock pixels
   for x = 0 to SW
      for y = 0 to SH

         xx1 = abs(x1 - x)
         yy1 = abs(y1 - y)
         xx2 = abs(x2 - x)
         yy2 = abs(y2 - y)
         xx3 = abs(x1 - x)
         yy3 = abs(y3 - y)

         col = tab(xx1, yy1) + tab(xx2, yy2) + tab(xx3, yy3)
         if col > 255 then col = 255
         dot x, y, pal(col)

      next y
   next z
   unlock pixels

   sync

until mouseclick()
end

for x = 0 to SW
      xx1 = abs(x1 - x)
      xx2 = abs(x2 - x)
      xx3 = abs(x3 - x)
      for y = 0 to SH
         yy1 = abs(y1 - y)
         yy2 = abs(y2 - y)
         yy3 = abs(y3 - y)
         col = tab(xx1, yy1) + tab(xx2, yy2) + tab(xx3, yy3)
         if col > 255 then col = 255
         dot x, y, pal(col)
      next y
   next z

function ABSrep(value)
   if value < 0
      value = 0-value
   endif
endfunction value

for x = 0 to SW
      xx1 = ABSrep(x1 - x)
      xx2 = ABSrep(x2 - x)
      xx3 = ABSrep(x3 - x)
      for y = 0 to SH
         yy1 = ABSrep(y1 - y)
         yy2 = ABSrep(y2 - y)
         yy3 = ABSrep(y3 - y)
         col = tab(xx1, yy1) + tab(xx2, yy2) + tab(xx3, yy3)
         if col > 255 then col = 255
         dot x, y, pal(col)
      next y
   next x