diff --git a/src/pixel/_impl/_px_circle_impl.scad b/src/pixel/_impl/_px_circle_impl.scad
new file mode 100644
index 00000000..873803cf
--- /dev/null
+++ b/src/pixel/_impl/_px_circle_impl.scad
@@ -0,0 +1,54 @@
+function _px_circle_y(f, y) = f >= 0 ? y - 1 : y;
+function _px_circle_ddf_y(f, ddf_y) = f >= 0 ? ddf_y + 2 : ddf_y;
+function _px_circle_f(f, ddf_y) = f >= 0 ? f + ddf_y : f;
+
+function _px_circle(f, ddf_x, ddf_y, x, y, filled) = 
+    x >= y ? [] : 
+    let(
+        ny = _px_circle_y(f, y),
+        nddf_y = _px_circle_ddf_y(f, ddf_y),
+        nx = x + 1,
+        nddf_x = ddf_x + 2,
+        nf = _px_circle_f(f, ddf_y) + nddf_x
+    )
+    concat(
+        filled ? 
+            concat(
+               [for(xi = -nx; xi <= nx; xi = xi + 1) [xi, -ny]],
+               [for(xi = -ny; xi <= ny; xi = xi + 1) [xi, -nx]],
+               [for(xi = -ny; xi <= ny; xi = xi + 1) [xi, nx]],
+               [for(xi = -nx; xi <= nx; xi = xi + 1) [xi, ny]]              
+            )
+            :
+            [  
+                [-nx, -ny], [nx, -ny],                 
+                [-ny, -nx], [ny, -nx],
+                [-ny, nx], [ny, nx],
+                [-nx, ny], [nx, ny]
+            ],
+        _px_circle(nf, nddf_x, nddf_y, nx, ny, filled)
+    );
+    
+function _px_circle_impl(radius, filled) =
+    let(
+        f = 1 - radius,
+        ddf_x = 1,
+        ddf_y = -2 * radius,
+        x = 0,
+        y = radius
+    )
+    concat(
+        filled ? 
+            concat(
+                [[0, radius], [0, -radius]],
+                [for(xi = -radius; xi <= radius; xi = xi + 1) [xi, 0]]
+            )
+            : 
+            [
+                [0, -radius],                
+                [-radius, 0], 
+                [radius, 0],
+                [0, radius]
+            ],
+        _px_circle(f, ddf_x, ddf_y, x, y, filled)
+    );
\ No newline at end of file
diff --git a/src/pixel/px_circle.scad b/src/pixel/px_circle.scad
index 45982054..a65279ee 100644
--- a/src/pixel/px_circle.scad
+++ b/src/pixel/px_circle.scad
@@ -8,57 +8,6 @@
 *
 **/ 
 
-function _px_circle_y(f, y) = f >= 0 ? y - 1 : y;
-function _px_circle_ddf_y(f, ddf_y) = f >= 0 ? ddf_y + 2 : ddf_y;
-function _px_circle_f(f, ddf_y) = f >= 0 ? f + ddf_y : f;
+use <pixel/_impl/_px_circle_impl.scad>;
 
-function _px_circle(f, ddf_x, ddf_y, x, y, filled) = 
-    x >= y ? [] : 
-    let(
-        ny = _px_circle_y(f, y),
-        nddf_y = _px_circle_ddf_y(f, ddf_y),
-        nx = x + 1,
-        nddf_x = ddf_x + 2,
-        nf = _px_circle_f(f, ddf_y) + nddf_x
-    )
-    concat(
-        filled ? 
-            concat(
-               [for(xi = -nx; xi <= nx; xi = xi + 1) [xi, -ny]],
-               [for(xi = -ny; xi <= ny; xi = xi + 1) [xi, -nx]],
-               [for(xi = -ny; xi <= ny; xi = xi + 1) [xi, nx]],
-               [for(xi = -nx; xi <= nx; xi = xi + 1) [xi, ny]]              
-            )
-            :
-            [  
-                [-nx, -ny], [nx, -ny],                 
-                [-ny, -nx], [ny, -nx],
-                [-ny, nx], [ny, nx],
-                [-nx, ny], [nx, ny]
-            ],
-        _px_circle(nf, nddf_x, nddf_y, nx, ny, filled)
-    );
-    
-function px_circle(radius, filled = false) =
-    let(
-        f = 1 - radius,
-        ddf_x = 1,
-        ddf_y = -2 * radius,
-        x = 0,
-        y = radius
-    )
-    concat(
-        filled ? 
-            concat(
-                [[0, radius], [0, -radius]],
-                [for(xi = -radius; xi <= radius; xi = xi + 1) [xi, 0]]
-            )
-            : 
-            [
-                [0, -radius],                
-                [-radius, 0], 
-                [radius, 0],
-                [0, radius]
-            ],
-        _px_circle(f, ddf_x, ddf_y, x, y, filled)
-    );
\ No newline at end of file
+function px_circle(radius, filled = false) = _px_circle_impl(radius, filled);
\ No newline at end of file
diff --git a/test/pixel/test_px_circle.scad b/test/pixel/test_px_circle.scad
index 19d2f675..1ae5b036 100644
--- a/test/pixel/test_px_circle.scad
+++ b/test/pixel/test_px_circle.scad
@@ -1,5 +1,5 @@
-include <unittest.scad>;
-include <pixel/px_circle.scad>;
+use <unittest.scad>;
+use <pixel/px_circle.scad>;
 
 module test_px_circle() {
     echo("==== test_px_circle ====");