Yin and yang: Difference between revisions

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 =={{header|UCB Logo}}==
 [[File:YinYangLogo.gif||200px|thumb|right|UCB Logo Graphic Output]]
 <lang logo>
+to taijitu :r
+  ; Draw a classic Taoist taijitu of the given radius centered on the current
+  ; turtle position. The "eyes" are placed along the turtle's heading, the
+  ; filled one in front, the open one behind.
+  ; don't bother doing anything if the pen is not down
+  if not pendown? [stop]
+  ; useful derivative values
+  localmake "r2 r/2
+  localmake "r4 r/4
+  localmake "r8 r/8
+  ; remember where we started
+  localmake "start  pos
+  ; draw outer circle
+  pendown
+  arc 360 :r
+  ; draw upper half of S
+  penup
+  forward r2
+  pendown
+  arc 180 r2
+  ; and filled inner eye
+  arc 360 r8
+  fill
+  ; draw lower half of S
+  penup
+  back r
+  pendown
+  arc -180 r2
+  ; other inner eye
+  arc  360 r8
+  ; fill this half of the symbol
+  penup
+  forward r4
+  pendown
+  fill
+  ; put the turtle back where it started
+  penup
+  setpos start
+  pendown
+end
+; demo code to produce image at right
+clearscreen
+pendown
+hideturtle
+taijitu 100
+penup
+forward 150
+left 90
+forward 150
+pendown
+taijitu 75
 </lang>