Added a diagonal iterator

.gitignore

@@ -1,3 +1,4 @@
 .dir-locals.el
 __pycache__
 *.png
+*.csv

prim_wallpaper/pickers/diagonal.py

@@ -0,0 +1,56 @@
+from math import sqrt
+
+
+def get_row_num(i):
+    return int((sqrt(8 * i + 1) - 1) / 2)
+
+
+def get_last_whole_i(row):
+    return (row * (row + 1)) // 2
+
+
+class DiagonalCounter:
+    def __init__(self, table_size):
+        self.table_size = table_size
+
+    def diagonal(self, i):
+        row = get_row_num(i)
+        last_whole_i = get_last_whole_i(row)
+        if row < self.table_size:
+            y = i - last_whole_i
+            x = row - y
+            return x, y
+        else:
+            x, y = self.diagonal(self.table_size ** 2 - (1 + i))
+            return self.table_size - x - 1, self.table_size - y - 1
+
+    def diagonal_reversed(self, i):
+        y, x = self.diagonal(i)
+        return x, y
+
+    def diagonal_then_reversed(self, i):
+        row = get_row_num(i)
+        if row > self.table_size:
+            row += 1
+        if row % 2 != 0:
+            return self.diagonal(i)
+        else:
+            return self.diagonal_reversed(i)
+
+
+if __name__ == "__main__":
+    import csv
+
+    d = DiagonalCounter(6)
+    for func in (d.diagonal, d.diagonal_reversed, d.diagonal_then_reversed):
+        output = list(
+            list(-1 for i in range(d.table_size)) for j in range(d.table_size)
+        )
+        indices = map(func, range(d.table_size ** 2))
+        for i, index in enumerate(indices):
+            x, y = index
+            output[y][x] = i
+
+        with open(func.__name__ + ".csv", "w", newline="") as file:
+            writer = csv.writer(file)
+            writer.writerows(output)

test.py

@@ -0,0 +1,3 @@
+from prim_wallpaper.make_wallpaper import make_wallpaper
+
+i = make_wallpaper(3, 5, 6)