Data update

Task/Bitmap-Midpoint-circle-algorithm/Rebol/bitmap-midpoint-circle-algorithm.rebol

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+Rebol [
+   title: "Rosetta code: Bitmap/Midpoint circle algorithm"
+   file:  %Bitmap-Midpoint_circle_algorithm.r3
+   url:   https://rosettacode.org/wiki/Bitmap/Midpoint_circle_algorithm
+]
+
+draw-circle: func [
+    "Draw a circle on an image using the Midpoint Circle Algorithm."
+    bitmap [image!] center [pair!] radius [integer!] color [tuple!]
+][
+    x:  center/x        ;; unpack center coords from pair for arithmetic
+    y:  center/y
+    dx: radius dy: 0
+    err: 1 - radius     ;; initial error term for midpoint decision
+
+    while [dx >= dy] [  ;; iterate through the first octant only
+        ;; Mirror the single computed point into all 8 octants at once,
+        ;; exploiting the 8-fold symmetry of the circle.
+        bitmap/(as-pair x + dx y + dy): color  ; octant 1
+        bitmap/(as-pair x - dx y + dy): color  ; octant 2
+        bitmap/(as-pair x + dx y - dy): color  ; octant 8
+        bitmap/(as-pair x - dx y - dy): color  ; octant 7
+        bitmap/(as-pair x + dy y + dx): color  ; octant 3
+        bitmap/(as-pair x - dy y + dx): color  ; octant 4 (swapped dx/dy)
+        bitmap/(as-pair x + dy y - dx): color  ; octant 5
+        bitmap/(as-pair x - dy y - dx): color  ; octant 6
+
+        dy: dy + 1      ;; advance one step along the minor axis
+
+        ;; Update the error term and conditionally step inward on dx.
+        ;; err < 0 means we are still inside the circle boundary
+        either err < 0 [
+            err: err + (2 * dy) + 1         ;; correct error for dy step
+        ][
+            dx: dx - 1                      ;; step inward on major axis
+            err: err + (2 * (dy - dx)) + 1  ;; correct error for both steps
+        ]
+    ]
+]
+
+img: make image! 29x29          ;; create a blank 29x29 canvas (white by default)
+draw-circle img 15x15  5 black  ;; small inner circle
+draw-circle img 15x15 10 red    ;; mid-size red ring
+draw-circle img 15x15 14 green  ;; large green ring, nearly fills the canvas
+
+;; scale up 10x with nearest-neighbour (Box) to keep pixel edges sharp
+img: resize/filter img 290 'Box
+save %midpoint-circles.png img
+try [view img]