Add option to hot spots

doc/json-config-parameters.md

@@ -358,6 +358,11 @@ changes in local image scale that occur due to distortions within the viewport.
 If set to a number, a fixed scaling is applied relative to the default hot spot
 size. Defaults to `false`.
 
+#### `sticky` (boolean)
+
+When `true`, the hot spot will stick to the edges of the screen, always visible. 
+Defaults to `false`.
+
 ### `hotSpotDebug` (boolean)
 
 When `true`, the mouse pointer's pitch and yaw are logged to the console when

src/js/pannellum.js

@@ -2081,6 +2081,10 @@ function renderHotSpot(hs) {
         // Apply transform
         coord[0] += (canvasWidth - hs.div.offsetWidth) / 2;
         coord[1] += (canvasHeight - hs.div.offsetHeight) / 2;
+        if (hs.sticky) {
+            coord[0] = Math.min(canvasWidth - hs.div.offsetWidth, Math.max(0, coord[0]));
+            coord[1] = Math.min(canvasHeight - hs.div.offsetHeight, Math.max(0, coord[1]));
+        }
         var transform = 'translate(' + coord[0] + 'px, ' + coord[1] +
             'px) translateZ(9999px) rotate(' + config.roll + 'deg)';
         if (hs.scale) {