opencv: facedetect: Add adaptive off-center dampingopencv

This is a naive adaptive-damping implementation
for out-of-center detection flickering. This
modification makes it so a the damping factor
is not harcoded but computed. Default is 5% of
magnitude.

Additionally:
Add braces around multiline if statement body (for clarity)

1 files changed, 17 insertions, 5 deletions

diff --git a/ext/opencv/gstfacedetect.cpp b/ext/opencv/gstfacedetect.cpp
index e78e4c43c..1f351ee3a 100644
--- a/ext/opencv/gstfacedetect.cpp
+++ b/ext/opencv/gstfacedetect.cpp
@@ -595,7 +595,11 @@ gst_face_detect_run_detector (GstFaceDetect * filter,
   }
 }
 
+/**
+ * Delta percentaje after wich position is considered off-center
+ */
 #define LINEAR_DAMPING_FACTOR 5
+
 /**
  * @gst_face_detect_get_leaning_side
  *
@@ -603,12 +607,17 @@ gst_face_detect_run_detector (GstFaceDetect * filter,
  * @pos: Object x coordinate
  * @ref_pos: Reference x coordinate
  * @side: result. DIRECTION_RIGHT or DIRECTION_LEFT. Untouched if inconclusive
+ * @displacement: Magnitude of min to max ramp
  */
 static inline void
-gst_face_detect_get_leaning_side (guint *side, gint reference, gint position) {
+gst_face_detect_get_leaning_side (guint *side, gint reference, gint position,
+    guint displacement) {
+
   g_assert (side);
 
-  if (ABS (position - reference) < LINEAR_DAMPING_FACTOR)
+  displacement =  displacement * LINEAR_DAMPING_FACTOR / 100;
+
+  if ((guint)ABS (position - reference) <= displacement)
     return;
 
   if (position > reference)
@@ -812,7 +821,8 @@ gst_face_detect_transform_ip (GstOpencvVideoFilter * base, GstBuffer * buf,
           center.y = cvRound ((rny + sr.y + h));
 
           /* left/right toggle */
-          gst_face_detect_get_leaning_side (&aim, f_center.x, center.x);
+          gst_face_detect_get_leaning_side (&aim, f_center.x, center.x,
+              r.width);
 
           axes.width = w;
           axes.height = h * 1.25;       /* tweak for nose form */
@@ -827,8 +837,10 @@ gst_face_detect_transform_ip (GstOpencvVideoFilter * base, GstBuffer * buf,
           center.x = cvRound ((rmx + sr.x + w));
           center.y = cvRound ((rmy + sr.y + h));
 
-          if (!aim)
-            gst_face_detect_get_leaning_side (&aim, f_center.x, center.x);
+          if (!aim) {
+            gst_face_detect_get_leaning_side (&aim, f_center.x, center.x,
+                r.width);
+          }
 
           axes.width = w * 1.5; /* tweak for mouth form */
           axes.height = h;