Make Viewport.style read-only. Improve the code.

docs/api/viewport.md

 
 ### style
 
-`viewport.style: string`
+`viewport.style: string, read-only`
 
 The style determines the way the viewport appears on the screen. Different styles are applicable to different [session modes](session.md#mode). The following are valid styles:
 

src/core/session.ts

         this._gizmos.visible = gizmos;
 
         // validate the mode
-        if(mode == 'immersive') {
-            if(viewport.style != 'best-fit' && viewport.style != 'stretch') {
-                Utils.warning(`Invalid viewport style \"${viewport.style}\" for the \"${mode}\" mode`);
-                viewport.style = 'best-fit';
-            }
-        }
-        else if(mode == 'inline') {
-            if(viewport.style != 'inline') {
-                Utils.warning(`Invalid viewport style \"${viewport.style}\" for the \"${mode}\" mode`);
-                viewport.style = 'inline';
-            }
-        }
-        else
+        if(mode != 'immersive' && mode != 'inline')
             throw new IllegalArgumentError(`Invalid session mode "${mode}"`);
 
-        // get media
-        const media = this.media;
-        const getMediaSize = () => media.size;
-
         // setup the viewport
         this._viewport = viewport;
-        this._viewport._init(getMediaSize);
+        this._viewport._init(() => this.media.size, mode);
 
         // setup the main loop
         this._setupUpdateLoop();

src/core/viewport.ts

 import { Nullable } from '../utils/utils';
 import { Resolution } from '../utils/resolution';
 import { Utils } from '../utils/utils';
+import { SessionMode } from './session';
 import { HUD, HUDContainer } from './hud';
 import { FullscreenButton } from '../ui/fullscreen-button';
 import { AREvent, AREventTarget, AREventListener } from '../utils/ar-events';
     /**
      * Set viewport style
      */
+    /*
     set style(value: ViewportStyle)
     {
         // note: the viewport style is independent of the session mode!
             this._style = value;
         }
     }
+    */
 
     /**
      * HUD
 
     /**
      * Initialize the viewport (when the session starts)
+     * @param getMediaSize
+     * @param sessionMode
      * @internal
      */
-    _init(getMediaSize: ViewportSizeGetter): void
+    _init(getMediaSize: ViewportSizeGetter, sessionMode: SessionMode): void
     {
+        // validate if the viewport style matches the session mode
+        if(sessionMode == 'immersive') {
+            if(this._style != 'best-fit' && this._style != 'stretch') {
+                Utils.warning(`Invalid viewport style \"${this._style}\" for the \"${sessionMode}\" mode`);
+                this._style = 'best-fit';
+                this._resizer.setStrategyByName(this._style);
+            }
+        }
+        else if(sessionMode == 'inline') {
+            if(this._style != 'inline') {
+                Utils.warning(`Invalid viewport style \"${this._style}\" for the \"${sessionMode}\" mode`);
+                this._style = 'inline';
+                this._resizer.setStrategyByName(this._style);
+            }
+        }
+
+        // set the media size getter
         this._mediaSize = getMediaSize;
 
+        // initialize the components
         this._containers.init();
         this._hud._init(HUD_ZINDEX);
         this._canvases.init();