implemented zigzag function

Author: ghallak

Diff for: encoder.py

@@ -0,0 +1,40 @@
+import numpy as np
+
+def zigzag(block):
+    # move the point to different directions
+    up    = lambda point: (point[0] - 1, point[1])
+    down  = lambda point: (point[0] + 1, point[1])
+    right = lambda point: (point[0], point[1] + 1)
+    left  = lambda point: (point[0], point[1] - 1)
+
+    up_right  = lambda point: up(right(point))
+    down_left = lambda point: down(left(point))
+
+    rows, cols = block.shape
+
+    # return true if point is inside the block bounds
+    def inbounds(point):
+        return 0 <= point[0] < rows and 0 <= point[1] < cols
+
+    # start in the top-left cell
+    point = (0, 0)
+
+    # TODO: rename this variable later
+    even = True
+
+    arr = np.empty((rows * cols, 1), np.int16);
+    for i in range(rows * cols):
+        arr[i] = block[point]
+        if even:
+            if inbounds(up_right(point)):
+                point = up_right(point)
+            else:
+                even = False
+                point = right(point) if inbounds(right(point)) else down(point)
+        else:
+            if inbounds(down_left(point)):
+                point = down_left(point)
+            else:
+                even = True
+                point = down(point) if inbounds(down(point)) else right(point)
+    return arr