[libchamplain] Fix 594963: Initial scrolling results in map being in Antarctica

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

commit 329ab16d3395a1ae395d2c55807d98246ccaa62c
Author: Pierre-Luc Beaudoin <pierre-luc pierlux com>
Date:   Sat Sep 12 23:25:44 2009 -0400

    Fix 594963: Initial scrolling results in map being in Antarctica
    
    The anchor that was being used was resulting in negative x or y values
    which were clamped back to positive values by TidyAdjustments.
    
    This patch makes sure that a new anchor is computed if the anchor
    would create negative x or y.

 champlain/champlain-view.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)
---
diff --git a/champlain/champlain-view.c b/champlain/champlain-view.c
index 9477a9e..0e66a9d 100644
--- a/champlain/champlain-view.c
+++ b/champlain/champlain-view.c
@@ -1319,8 +1319,8 @@ champlain_view_new (void)
 
 static void
 view_update_anchor (ChamplainView *view,
-    gint x,
-    gint y)
+    gint x,  /* Absolute x */
+    gint y)  /* Absolute y */
 {
   ChamplainViewPrivate *priv = view->priv;
   gboolean need_anchor = FALSE;
@@ -1331,7 +1331,9 @@ view_update_anchor (ChamplainView *view,
 
   if (priv->anchor_zoom_level != priv->zoom_level ||
       x - priv->anchor.x + priv->viewport_size.width >= G_MAXINT16 ||
-      y - priv->anchor.y + priv->viewport_size.height >= G_MAXINT16)
+      y - priv->anchor.y + priv->viewport_size.height >= G_MAXINT16 ||
+      x - priv->anchor.x + priv->viewport_size.width <= 0 ||
+      y - priv->anchor.y + priv->viewport_size.height <= 0 )
     need_update = TRUE;
 
   if (need_anchor && need_update)
@@ -1355,6 +1357,7 @@ view_update_anchor (ChamplainView *view,
         priv->anchor.y = max;
 
       priv->anchor_zoom_level = priv->zoom_level;
+      DEBUG ("New Anchor (%f, %f) at (%d, %d)", priv->anchor.x, priv->anchor.y, x, y);
     }
 
   if (need_anchor == FALSE)
@@ -1362,8 +1365,8 @@ view_update_anchor (ChamplainView *view,
       priv->anchor.x = 0;
       priv->anchor.y = 0;
       priv->anchor_zoom_level = priv->zoom_level;
+      DEBUG ("Clear Anchor at (%d, %d)", x, y);
     }
-  DEBUG ("New Anchor (%f, %f) for (%d, %d)", priv->anchor.x, priv->anchor.y, x, y);
 }
 
 /**
@@ -1397,6 +1400,8 @@ champlain_view_center_on (ChamplainView *view,
   x = champlain_map_source_get_x (priv->map_source, priv->zoom_level, longitude);
   y = champlain_map_source_get_y (priv->map_source, priv->zoom_level, latitude);
 
+  DEBUG ("Centering on %f, %f (%d, %d)", latitude, longitude, x, y);
+
   view_update_anchor (view, x, y);
 
   x -= priv->anchor.x;
@@ -1610,6 +1615,8 @@ champlain_view_set_zoom_level (ChamplainView *view,
   if (!map_zoom_to (priv->map, priv->map_source, zoom_level))
     return;
 
+  DEBUG ("Zooming to %d", zoom_level);
+
   priv->zoom_level = zoom_level;
   /* Fix to bug 575133: keep the lat,lon as it gets set to a wrong value
    * when resizing the viewport, when passing from zoom_level 7 to 6