add px_surround

src/experimental/_impl/_px_surround_impl.scad

@@ -0,0 +1,35 @@
+use <experimental/has.scad>;
+
+function _px_surround_corner_value(pts, x, y) =
+    let(
+        c1 = has(pts, [x, y - 1]) || has(pts, [x - 1, y - 1]) ? 1 : 0,
+        c2 = has(pts, [x - 1, y]) || has(pts, [x - 1, y + 1]) ? 2 : 0,
+        c3 = has(pts, [x, y + 1]) || has(pts, [x + 1, y + 1]) ? 4 : 0,
+        c4 = has(pts, [x + 1, y]) || has(pts, [x + 1, y - 1]) ? 8 : 0
+    )
+    c1 + c2 + c3 + c4;
+
+_px_surround_dir_table = [
+    [4,  0], [6,  0], [7, 0],    // RIGHT
+    [8,  1], [12, 1], [14, 1],   // DOWN
+    [2,  2], [3,  2], [11, 2],   // UP
+    [1,  3], [9,  3], [13, 3]    // LEFT
+];
+function _px_surround_dir(cr_value) = 
+    lookup(cr_value, _px_surround_dir_table);
+
+_px_surround_nxt_offset = [
+    [1,  0],   // RIGHT
+    [0, -1],   // DOWN
+    [0,  1],   // UP
+    [-1, 0]    // LEFT
+];
+function _px_surround_travel(pts, p, fst) = 
+    let(
+        dir_i = _px_surround_dir(_px_surround_corner_value(pts, p[0], p[1])),
+        nxt_p = p + _px_surround_nxt_offset[dir_i]
+    )
+    nxt_p == fst ? [p] :
+    concat(
+        [p], _px_surround_travel(pts, nxt_p, fst)
+    );

src/experimental/px_surround.scad

@@ -0,0 +1,10 @@
+use <experimental/_impl/_px_surround_impl.scad>;
+use <util/sort.scad>;
+
+function px_surround(points) = 
+    let(
+        // always start from the left-bottom pt
+        sortedXY = sort(sort(points, by = "x"), by = "y"),
+        fst = sortedXY[0] + [-1, -1]
+    )
+    _px_surround_travel(sortedXY, fst, fst);