[gtk+/xi2: 452/1239] Add helper functions to know data relative to the coordinates of two events.

[Carlos Garnacho <carlosg src gnome org>]

commit edf58dcd6380d9968fa6574d84f018b0d2172f4d
Author: Carlos Garnacho <carlos lanedo com>
Date:   Sun Jul 5 15:28:55 2009 +0100

    Add helper functions to know data relative to the coordinates of two events.
    
    There are functions to return the distance, angle and center between two
    GdkEvents with x/y info.

 gdk/gdkevents.c |   90 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 gdk/gdkevents.h |   12 +++++++
 2 files changed, 102 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkevents.c b/gdk/gdkevents.c
index 24a29a1..079da43 100644
--- a/gdk/gdkevents.c
+++ b/gdk/gdkevents.c
@@ -26,6 +26,7 @@
 
 #include "config.h"
 #include <string.h>		/* For memset() */
+#include <math.h>
 
 #include "gdk.h"
 #include "gdkinternals.h"
@@ -889,6 +890,95 @@ gdk_event_request_motions (const GdkEventMotion *event)
     gdk_device_get_state (event->device, event->window, NULL, NULL);
 }
 
+static gboolean
+gdk_events_get_axis_distances (GdkEvent *event1,
+                               GdkEvent *event2,
+                               gdouble  *x_distance,
+                               gdouble  *y_distance,
+                               gdouble  *distance)
+{
+  gdouble x1, x2, y1, y2;
+  gdouble xd, yd;
+
+  if (!gdk_event_get_coords (event1, &x1, &y1) ||
+      !gdk_event_get_coords (event2, &x2, &y2))
+    return FALSE;
+
+  xd = x2 - x1;
+  yd = y2 - y1;
+
+  if (x_distance)
+    *x_distance = xd;
+
+  if (y_distance)
+    *y_distance = yd;
+
+  if (distance)
+    *distance = sqrt ((xd * xd) + (yd * yd));
+
+  return TRUE;
+}
+
+gboolean
+gdk_events_get_distance (GdkEvent *event1,
+                         GdkEvent *event2,
+                         gdouble  *distance)
+{
+  return gdk_events_get_axis_distances (event1, event2,
+                                        NULL, NULL,
+                                        distance);
+}
+
+gboolean
+gdk_events_get_angle (GdkEvent *event1,
+                      GdkEvent *event2,
+                      gdouble  *angle)
+{
+  gdouble x_distance, y_distance, distance;
+
+  if (!gdk_events_get_axis_distances (event1, event2,
+                                      &x_distance, &y_distance,
+                                      &distance))
+    return FALSE;
+
+  if (angle)
+    {
+      *angle = atan2 (x_distance, y_distance);
+
+      /* Invert angle */
+      *angle = (2 * G_PI) - *angle;
+
+      /* Shift it 90° */
+      *angle += G_PI / 2;
+
+      /* And constraint it to 0°-360° */
+      *angle = fmod (*angle, 2 * G_PI);
+    }
+
+  return TRUE;
+}
+
+gboolean
+gdk_events_get_center (GdkEvent *event1,
+                       GdkEvent *event2,
+                       gdouble  *x,
+                       gdouble  *y)
+{
+  gdouble x1, x2, y1, y2;
+
+  if (!gdk_event_get_coords (event1, &x1, &y1) ||
+      !gdk_event_get_coords (event2, &x2, &y2))
+    return FALSE;
+
+  if (x)
+    *x = (x2 + x1) / 2;
+
+  if (y)
+    *y = (y2 + y1) / 2;
+
+  return TRUE;
+}
+
 /**
  * gdk_event_set_screen:
  * @event: a #GdkEvent
diff --git a/gdk/gdkevents.h b/gdk/gdkevents.h
index b3a05af..21b5a2d 100644
--- a/gdk/gdkevents.h
+++ b/gdk/gdkevents.h
@@ -539,6 +539,18 @@ gboolean  gdk_event_get_axis            (const GdkEvent  *event,
                                          GdkAxisUse       axis_use,
                                          gdouble         *value);
 void      gdk_event_request_motions     (const GdkEventMotion *event);
+
+gboolean  gdk_events_get_distance       (GdkEvent        *event1,
+                                         GdkEvent        *event2,
+                                         gdouble         *distance);
+gboolean  gdk_events_get_angle          (GdkEvent        *event1,
+                                         GdkEvent        *event2,
+                                         gdouble         *angle);
+gboolean  gdk_events_get_center         (GdkEvent        *event1,
+                                         GdkEvent        *event2,
+                                         gdouble         *x,
+                                         gdouble         *y);
+
 void	  gdk_event_handler_set 	(GdkEventFunc    func,
 					 gpointer        data,
 					 GDestroyNotify  notify);