[libshumate] marker-layer: Properly position markers

[Corentin Noël <corentinnoel src gnome org>]

commit 49853360f39ad72a452bebffc736fa7d7e498223
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Mar 3 23:46:03 2021 -0300

    marker-layer: Properly position markers
    
    Commit 9e138d2 reworked allocation of ShumateMarkerLayer, but it wrongly
    used the x/y positions relative to the *marker* and offset by half of the
    width/height. The correct coordinate transform is relative to the mark layer,
    then offsetting by half of the marker size to centralize it.
    
    Use the correct relative widget to translate between geographic coordinates
    and pixel coordinates.

 shumate/shumate-marker-layer.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)
---
diff --git a/shumate/shumate-marker-layer.c b/shumate/shumate-marker-layer.c
index dd57ced..ae0f02f 100644
--- a/shumate/shumate-marker-layer.c
+++ b/shumate/shumate-marker-layer.c
@@ -130,11 +130,12 @@ update_marker_visibility (ShumateMarkerLayer *layer,
   width = gtk_widget_get_width (GTK_WIDGET (layer));
   height = gtk_widget_get_height (GTK_WIDGET (layer));
 
-  x = roundf (shumate_viewport_longitude_to_widget_x (viewport, GTK_WIDGET (marker), lon) + width/2.f);
-  y = roundf (shumate_viewport_latitude_to_widget_y (viewport, GTK_WIDGET (marker), lat) + height/2.f);
-
   gtk_widget_measure (GTK_WIDGET (marker), GTK_ORIENTATION_HORIZONTAL, -1, 0, &marker_width, NULL, NULL);
   gtk_widget_measure (GTK_WIDGET (marker), GTK_ORIENTATION_VERTICAL, -1, 0, &marker_height, NULL, NULL);
+
+  x = roundf (shumate_viewport_longitude_to_widget_x (viewport, GTK_WIDGET (layer), lon) - marker_width/2.f);
+  y = roundf (shumate_viewport_latitude_to_widget_y (viewport, GTK_WIDGET (layer), lat) - marker_height/2.f);
+
   within_viewport = x > -marker_width && x <= width &&
                     y > -marker_height && y <= height &&
                     marker_width < width && marker_height < height;
@@ -215,6 +216,7 @@ shumate_marker_layer_size_allocate (GtkWidget *widget,
       gboolean within_viewport;
       double lon, lat;
       double x, y;
+      int marker_width, marker_height;
 
       if (!gtk_widget_should_layout (child))
         continue;
@@ -222,14 +224,16 @@ shumate_marker_layer_size_allocate (GtkWidget *widget,
       lon = shumate_location_get_longitude (SHUMATE_LOCATION (child));
       lat = shumate_location_get_latitude (SHUMATE_LOCATION (child));
 
-      x = roundf (shumate_viewport_longitude_to_widget_x (viewport, child, lon) + width/2.f);
-      y = roundf (shumate_viewport_latitude_to_widget_y (viewport, child, lat) + height/2.f);
+      gtk_widget_measure (child, GTK_ORIENTATION_HORIZONTAL, -1, 0, &marker_width, NULL, NULL);
+      gtk_widget_measure (child, GTK_ORIENTATION_VERTICAL, -1, 0, &marker_height, NULL, NULL);
+
+      x = roundf (shumate_viewport_longitude_to_widget_x (viewport, widget, lon) - marker_width/2.f);
+      y = roundf (shumate_viewport_latitude_to_widget_y (viewport, widget, lat) - marker_height/2.f);
 
       allocation.x = x;
       allocation.y = y;
-
-      gtk_widget_measure (child, GTK_ORIENTATION_HORIZONTAL, -1, 0, &allocation.width, NULL, NULL);
-      gtk_widget_measure (child, GTK_ORIENTATION_VERTICAL, -1, 0, &allocation.height, NULL, NULL);
+      allocation.width = marker_width;
+      allocation.height = marker_height;
 
       within_viewport = x > -allocation.width && x <= width &&
                         y > -allocation.height && y <= height &&