add px_gray

src/pixel/px_gray.scad

@@ -0,0 +1,36 @@
+function _px_gray_row(r_count, row_bits, width, height, center, invert) =
+    let(
+        half_w = width / 2,
+        half_h = height / 2,
+        offset_x = center ? 0 : half_w,
+        offset_y = center ? 0 : half_h,
+        level = invert ? 0 : 255
+    ) 
+    [
+        for(i = 0; i < width; i = i + 1) 
+            if(row_bits[i] != level) 
+                [
+                    i - half_w + offset_x, 
+                    r_count + offset_y, 
+                    invert ? row_bits[i] / 255 : 1 - row_bits[i] / 255
+                ]
+    ];
+
+function px_gray(levels, size, center = false, invert = false) = 
+    let(
+        squar = sqrt(len(levels)),
+        siz = is_undef(size) ? [squar, squar] : size,
+        width = siz[0],
+        height = siz[1],
+        rows = [
+            for(row = height - 1; row > -1; row = row - 1)
+                [for(column = 0; column < width; column = column + 1)
+                    levels[row * width + column]]
+        ],
+        offset_i = height / 2
+    )
+    [
+        for(i = 0; i < height; i = i + 1) 
+        let(row = _px_gray_row(i - offset_i, rows[i], width, height, center, invert))
+        if(row != []) each row
+    ];