gst-test-perspective.py: add an example about a rotation transform

diff --git a/python/gst-test-perspective.py b/python/gst-test-perspective.py
index 6ddf5b0..1b094c2 100755 (executable)
--- a/python/gst-test-perspective.py
+++ b/python/gst-test-perspective.py
@@ -4,6 +4,7 @@
 
 import cv2
 import numpy as np
+from math import cos, sin, radians
 
 import gi
 gi.require_version('Gst', '1.0')
@@ -27,6 +28,24 @@ def calc_matrix():
     return inv_mat.flatten()
 
 
+def calc_rotation_matrix():
+    width, height = 800, 480
+
+    pivot = (width / 2, height / 2)
+    angle = 10
+    theta = radians(angle)
+
+    # The dimensions of the bounding box of the rotated rectangle
+    W = width * abs(cos(theta)) + height * abs(sin(theta))
+    H = width * abs(sin(theta)) + height * abs(cos(theta))
+
+    scale_factor = 1 / min(width / W, height / H)
+
+    mat = cv2.getRotationMatrix2D(pivot, angle, scale_factor)
+    mat = np.vstack([mat, [0, 0, 1]])
+
+    return mat.flatten()
+
 
 def main():
     pipeline = Gst.ElementFactory.make('pipeline', None)
@@ -40,7 +59,7 @@ def main():
 
     print perspective.get_property("matrix")
 
-    M = calc_matrix()
+    M = calc_rotation_matrix()
     perspective.set_property("matrix", M)
     print perspective.get_property("matrix")