Fix Issue #17 repeated rescaling of image map.

Repeated scaling of image map will after a while make the image map
coordinates diverge from the location of the airport on the map. To fix this
the coordinates of the image map will be cached and used for calculating
the new image map coordinates when scaling is applie.

This patch also now resizes the airport locator circle so it is not a tiny circle
when zoomed to 200%.

Author: ohommes

common/scripts/map_actions.js

@@ -221,7 +221,7 @@ function locateAirport(list) {
   refreshCanvas();
   x = parseInt(coords[0]);
   y = parseInt(coords[1]);
-  drawHighlight(context,x,y,radius);
+  drawHighlight(context,x,y,radius * properties.zoom);
 
   // Make the airport the focus
   window.scrollTo(x-window.innerWidth/2,y-window.innerHeight/2);
@@ -538,14 +538,21 @@ function selectVisibility(list) {
   refreshCanvas();
 }
 
+var hotspots;
+function storeMapCoordinates() {
+  var imgMap = document.getElementById("imgMap");
+  hotspots = [];
+  for (area of imgMap.children) hotspots.push(area);
+}
 
 // Scale the image map coordinates to match the airport overlay image
 function scaleMap(scale) {
   var imageMap = document.getElementById("imgMap");
   var areas  = imageMap.children;
+  i = 0;
   for (area of areas) {
-      area.coordArr = area.coords.split(',');
-      area.coords = area.coordArr.map(coord => Math.round(coord * scale)).join(',');
+      var coordArr = hotspots[i++].coords.split(',');
+      area.coords = coordArr.map(coord => Math.round(coord * scale)).join(',');
       if (area.alt == "Legend") properties.legend = area.coords;
       if (area.alt == "Bullseye") bullseye.coords = area.coords;
   }
@@ -1641,7 +1648,9 @@ window.onload = function(e) {
 
     // Adjust map to used scale
   // Safari will slow beyond 3840 canvas size
+  storeMapCoordinates();
   scaleMap(3840/4096);
+  storeMapCoordinates();
 
   // Setup the Layers to be rendered on the main canvas
   setupLayer(layer.mission, canvas.width, canvas.height );