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

[experiments/gstreamer.git] / python / gst-test-perspective.py

diff --git a/python/gst-test-perspective.py b/python/gst-test-perspective.py
index b51591a..1b094c2 100755 (executable)
--- a/python/gst-test-perspective.py
+++ b/python/gst-test-perspective.py
@@ -1,8 +1,10 @@
 #!/usr/bin/env python
 
-# test program for the "perspective" geometric tranform element
+# test program for the "perspective" geometric transform element
 
-import cv
+import cv2
+import numpy as np
+from math import cos, sin, radians
 
 import gi
 gi.require_version('Gst', '1.0')
@@ -17,17 +19,32 @@ def calc_matrix():
     top_x_shift = 200
 
     width, height = 800, 480
-    corners = [(0, 0), (width, 0), (width, height), (0, height)]
-    target = [(top_x_shift, 0), (width - top_x_shift, 0), (width, height), (0, height)]
+    corners = np.array([(0, 0), (width, 0), (width, height), (0, height)], dtype=np.float32)
+    target = np.array([(top_x_shift, 0), (width - top_x_shift, 0), (width, height), (0, height)], dtype=np.float32)
 
-    mat = cv.CreateMat(3, 3, cv.CV_64F)
-    cv.GetPerspectiveTransform(corners, target, mat)
+    mat = cv2.getPerspectiveTransform(corners, target)
+    ret, inv_mat = cv2.invert(mat)
 
-    inv_mat = cv.CreateMat(3, 3, cv.CV_64F)
-    cv.Invert(mat, inv_mat)
+    return inv_mat.flatten()
 
-    matrix = [inv_mat[j, i] for j in range(mat.rows) for i in range(mat.cols)]
-    return matrix
+
+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():
@@ -42,7 +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")