[libchamplain/libchamplain-0-4] Move distance computation in MapSource

[Pierre-Luc Beaudoin <plbeaudoin src gnome org>]

commit 10078a898a9e1a2ece6f09f76950f46f73636c30
Author: Pierre-Luc Beaudoin <pierre-luc pierlux com>
Date:   Tue Dec 15 10:15:29 2009 -0500

    Move distance computation in MapSource
    
    with other projection specific calculations

 champlain/champlain-map-source.c |   32 ++++++++++++++++++++++++++++++++
 champlain/champlain-map-source.h |    5 +++++
 champlain/champlain-view.c       |   23 ++++++-----------------
 3 files changed, 43 insertions(+), 17 deletions(-)
---
diff --git a/champlain/champlain-map-source.c b/champlain/champlain-map-source.c
index 47a28cc..c90f43e 100644
--- a/champlain/champlain-map-source.c
+++ b/champlain/champlain-map-source.c
@@ -730,3 +730,35 @@ champlain_map_source_set_id (ChamplainMapSource *map_source,
   g_object_notify (G_OBJECT (map_source), "id");
 }
 
+#define EARTH_RADIUS 6378137 /* meters, Equatorial radius */
+
+/**
+ * champlain_map_source_get_meters_per_pixel:
+ * @map_source: a #ChamplainMapSource
+ * @zoom_level: the zoom level
+ * @latitude: a latitude
+ * @longitude: a longitude
+ *
+ * Returns: the meters per pixel at the position on the map using this map source's projection.
+ *
+ * Since: 0.4.3
+ */
+gfloat
+champlain_map_source_get_meters_per_pixel (ChamplainMapSource *map_source,
+    gint zoom_level,
+    gdouble latitude,
+    gdouble longitude)
+{
+  g_return_val_if_fail (CHAMPLAIN_IS_MAP_SOURCE (map_source), 0);
+
+  /* Width is in pixels. (1 px)
+     m/px = radius_at_latitude / width_in_pixels
+     k = radius of earth = 6 378.1 km
+     radius_at_latitude = 2Ï? * k * sin (Ï?/2-θ)
+  */
+
+  ChamplainMapSourcePrivate *priv = map_source->priv;
+  // FIXME: support other projections
+  return 2 * M_PI * EARTH_RADIUS * sin (M_PI/2 - M_PI / 180 * latitude) /
+    (priv->tile_size * champlain_map_source_get_row_count (map_source, zoom_level));
+}
diff --git a/champlain/champlain-map-source.h b/champlain/champlain-map-source.h
index 3845926..d2c9732 100644
--- a/champlain/champlain-map-source.h
+++ b/champlain/champlain-map-source.h
@@ -114,6 +114,11 @@ void champlain_map_source_set_projection (ChamplainMapSource *map_source,
     ChamplainMapProjection projection);
 ChamplainMapProjection champlain_map_source_get_projection (ChamplainMapSource *map_source);
 
+gfloat champlain_map_source_get_meters_per_pixel (ChamplainMapSource *map_source,
+    gint zoom_level,
+    gdouble latitude,
+    gdouble longitude);
+
 G_END_DECLS
 
 #endif
diff --git a/champlain/champlain-view.c b/champlain/champlain-view.c
index ca39f0a..4e9cc89 100644
--- a/champlain/champlain-view.c
+++ b/champlain/champlain-view.c
@@ -1004,37 +1004,26 @@ update_scale (ChamplainView *view)
 {
   ClutterActor *text;
   ChamplainViewPrivate *priv = view->priv;
-  ChamplainZoomLevel *level;
   gfloat m_per_pixel;
+  gfloat width = SCALE_WIDTH;
   gchar *label;
-  ChamplainTile *tile;
-
-  /* Width is in pixels.
-     m/px = radius_at_latitude / width_in_pixels
-     k = radius of earth = 6 378.1 km
-     radius_at_latitude = 2Ï? * k * sin (Ï?/2-θ)
-
-  */
 
   if (! priv || !priv->map || !priv->map->current_level)
     return;
 
   if (priv->show_scale)
     {
-      clutter_actor_show(priv->scale_actor);
+      clutter_actor_show (priv->scale_actor);
     }
   else
     {
-      clutter_actor_hide(priv->scale_actor);
+      clutter_actor_hide (priv->scale_actor);
       return;
     }
 
-  level = priv->map->current_level;
-  tile = champlain_zoom_level_get_nth_tile(level, 0);
-  m_per_pixel = 2 * M_PI * 6378100 * sin(M_PI/2 - M_PI / 180*priv->latitude) /
-    (champlain_tile_get_size (tile) * champlain_zoom_level_get_width (level));
-
-  label = g_strdup_printf("%.2f km", (m_per_pixel * SCALE_WIDTH) / 1000);
+  m_per_pixel = champlain_map_source_get_meters_per_pixel (priv->map_source,
+      priv->zoom_level, priv->latitude, priv->longitude) * width;
+  label = g_strdup_printf ("%.2f km", m_per_pixel / 1000);
 
   text = clutter_container_find_child_by_name (CLUTTER_CONTAINER (priv->scale_actor), "scale-label");
   clutter_text_set_text (CLUTTER_TEXT (text), label);