Bitmap/Midpoint circle algorithm: Difference between revisions

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     call draw_circle_toch(img%channel, c, radius, lum)
   end subroutine draw_circle_sc</lang>
+=={{header|J}}==
+'''Solution:'''<br>
+Using definitions from [[Basic bitmap storage#J|Basic bitmap storage]].
+<lang j>NB.*getBresenhamCircle v Returns points for a circle given center and radius
+NB. y is: y0 x0 radius
+getBresenhamCircle=: monad define
+  'y0 x0 radius'=. y
+  x=. 0
+  y=. radius
+  f=. -. radius
+  pts=. 0 2$0
+  while. x <: y do.
+    pts=. pts , x , y
+    if. f >: 0 do.
+      y=. <:y
+      f=. f + _2&* y      NB. _2 * y
+    end.
+    x=. >:x
+    f =. f + 2&(>:@*) x   NB. 1 + 2 * x
+  end.
+  offsets=. (,|."1) (1 _1 {~ #: i.4) *"1"1 _ pts
+  ~.,/ (x0,y0) +"1 offsets
+)
+NB.*drawCircle v Draws circle (x) on image (y)
+NB. x is: 2-item list (y0 x0 radius) ; (color)
+drawCircle=: (1&{:: ;~ [: ; [: <@getBresenhamCircle"1 (0&{::))@[ setPixels ]
+</lang>
+'''Example usage:'''
+<lang j>   myimg=: 0 255 0 makeRGB 25 25                              NB. 25 by 25 green image
+   myimg=: (12 12 12 ; 255 0 0) drawCircle myimg              NB. draw red circle with radius 12
+   viewRGB ((12 12 9 ,: 12 12 6) ; 0 0 255) drawCircle myimg  NB. draw two more concentric circles
+   '+' (<"1 getBresenhamCircle 7 7 7)} 15 15$ ' '
+     +++++
+   ++     ++
+  +         +
+ +           +
+ +           +
++             +
++             +
++             +
++             +
++             +
+ +           +
+ +           +
+  +         +
+   ++     ++
+     +++++     </lang>
 =={{header|Modula-3}}==