Add common image rotation as special cases

doc/source/doxygen-docs/changelog.md

@@ -2,6 +2,8 @@
 
 # Version 2.14.3: UNRELEASED
 - Changes in libraries:
+  - \ref mrpt_img_grp:
+    - mrpt::img::CImage::rotateImage(): Special angles 90,-90, 180 are handled as expected with a quick image transformation and rotation.
   - \ref mrpt_nav_grp:
     - mrpt::nav::CWaypointsNavigator: New parameter "minimum_target_approach_per_step" and feature to keep approaching waypoints until no significant improvement is done.
   - \ref mrpt_ros1bridge_grp and mrpt_ros2bridge_grp:

libs/img/include/mrpt/img/CImage.h

@@ -261,8 +261,10 @@ class CImage : public mrpt::serialization::CSerializable, public CCanvas
       unsigned int height,
       TInterpolationMethod interp = IMG_INTERP_CUBIC) const;
 
-  /** Rotates the image by the given angle around the given center point, with
+  /** Rotates the image by the given angle (in radians) around the given center point, with
    * an optional scale factor.
+   * The output image will have the same size as the input, except if angle is exactly ±90 degrees,
+   * in which case a quick image rotation (switching height and widht) will be performed instead.
    * \sa resize, scaleImage
    */
   void rotateImage(

libs/img/src/CImage.cpp

@@ -1797,6 +1797,21 @@ void CImage::rotateImage(
   // Detect in-place operation and make a deep copy if needed:
   if (out_img.m_impl->img.data == srcImg.data) srcImg = srcImg.clone();
 
+  // quick rotation?
+  if (std::abs(M_PI * 0.5 - std::abs(ang)) < 1e-3 || std::abs(M_PI - std::abs(ang)) < 1e-3)
+  {
+    int rotCode = 0;
+    if (std::abs(M_PI * 0.5 - ang) < 1e-3)
+      rotCode = cv::ROTATE_90_COUNTERCLOCKWISE;
+    else if (std::abs(-M_PI * 0.5 - ang) < 1e-3)
+      rotCode = cv::ROTATE_90_CLOCKWISE;
+    else if (std::abs(M_PI - ang) < 1e-3)
+      rotCode = cv::ROTATE_180;
+
+    cv::rotate(srcImg, out_img.m_impl->img, rotCode);
+  }
+  // else: general rotation:
+
   out_img.resize(getWidth(), getHeight(), getChannelCount());
 
   // Based on the blog entry: