Add config parameter to use `minHfov` for `multires` panoramas.

Normally, the value of `minHfov` is ignored for said panoramas, and an
automatically calculated value is used instead.

doc/json-config-parameters.md

@@ -151,7 +151,16 @@ Defaults to `undefined`, so the viewer center can reach `-90` / `90`.
 ### `minHfov` and `maxHfov` (number)
 
 Sets the minimum / maximum horizontal field of view, in degrees, that the
-viewer can be set to. Defaults to `50` / `120`.
+viewer can be set to. Defaults to `50` / `120`. Unless the `multiResMinHfov`
+parameter is set to `true`, the `minHfov` parameter is ignored for
+`multires` panoramas.
+
+
+### `multiResMinHfov` (boolean)
+
+When set to `false`, the `minHfov` parameter is ignored for `multires`
+panoramas; an automatically calculated minimum horizontal field of view is used
+instead. Defaults to `false`.
 
 
 ### `compass` (boolean)

src/js/pannellum.js

@@ -72,6 +72,7 @@ var config,
 var defaultConfig = {
     hfov: 100,
     minHfov: 50,
+    multiResMinHfov: false,
     maxHfov: 120,
     pitch: 0,
     minPitch: undefined,
@@ -2144,7 +2145,7 @@ function zoomOut() {
 function constrainHfov(hfov) {
     // Keep field of view within bounds
     var minHfov = config.minHfov;
-    if (config.type == 'multires' && renderer) {
+    if (config.type == 'multires' && renderer && config.multiResMinHfov) {
         minHfov = Math.min(minHfov, renderer.getCanvas().width / (config.multiRes.cubeResolution / 90 * 0.9));
     }
     if (minHfov > config.maxHfov) {