From 7e751cae91c2c08e2ba56912096eadd42f16e356 Mon Sep 17 00:00:00 2001
From: Eugene Maksymenko <maxigene@gmail.com>
Date: Wed, 28 Sep 2022 12:21:38 +0300
Subject: [PATCH] Keep map scale by adopting field of view on view port resize

---
 src/BasicWorldWindowController.js |  2 +-
 src/WorldWindow.js                | 18 +++++++++++++++---
 src/geom/Camera.js                | 23 +++++++++++++++++++++--
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/src/BasicWorldWindowController.js b/src/BasicWorldWindowController.js
index 48b519a1ee..0590006bd6 100644
--- a/src/BasicWorldWindowController.js
+++ b/src/BasicWorldWindowController.js
@@ -457,7 +457,7 @@ define([
             // Clamp tilt to between 0 and +90 to prevent the viewer from going upside down.
             lookAt.tilt = WWMath.clamp(lookAt.tilt, 0, 90);
 
-            // Normalize heading to between -180 and +180.
+            // Normalize roll to between -180 and +180.
             lookAt.roll = Angle.normalizedDegrees(lookAt.roll);
 
             // Apply 2D limits when the globe is 2D.
diff --git a/src/WorldWindow.js b/src/WorldWindow.js
index 6a4b37ffae..d6215c8326 100644
--- a/src/WorldWindow.js
+++ b/src/WorldWindow.js
@@ -175,7 +175,7 @@ define([
              * @type {Rectangle}
              * @readonly
              */
-            this.viewport = new Rectangle(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
+            this.viewport = new Rectangle(0, 0, 0, 0);
 
             /**
              * The globe displayed.
@@ -811,13 +811,25 @@ define([
                 width = gl.canvas.clientWidth * this.pixelScale,
                 height = gl.canvas.clientHeight * this.pixelScale;
 
-            if (gl.canvas.width != width ||
-                gl.canvas.height != height) {
+            if (gl.canvas.width != width || gl.canvas.height != height
+                || this.viewport.width === 0 || this.viewport.height === 0) {
 
                 // Make the canvas drawing buffer size match its screen size.
                 gl.canvas.width = width;
                 gl.canvas.height = height;
 
+                // Keep map scale by adopting field of view on view port resize
+                if (this.viewport.height !== 0) {
+                    try {
+                        this.camera.fieldOfView *= height / this.viewport.height;
+                    } catch (ignore) {
+                        // Keep original field of view in case new one does not fit requirements
+                    }
+                } else if (width > height) {
+                    // Apply initial field of view to the longest viewport side
+                    this.camera.fieldOfView *= height / width;
+                }
+
                 // Set the WebGL viewport to match the canvas drawing buffer size.
                 gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
                 this.viewport = new Rectangle(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
diff --git a/src/geom/Camera.js b/src/geom/Camera.js
index a4dc60fc3a..7217c3122c 100644
--- a/src/geom/Camera.js
+++ b/src/geom/Camera.js
@@ -42,6 +42,7 @@ define([
 
             /**
              * Camera tilt, in degrees.
+             * @type {Number}
              * @default 0
              */
             this.tilt = 0;
@@ -53,13 +54,31 @@ define([
              */
             this.roll = 0;
 
+            // Intentionally not documented
+            this._fieldOfView = 45;
+        };
+
+        Object.defineProperties(Camera.prototype, {
             /**
              * Camera vertical field of view, in degrees
              * @type {Number}
              * @default 45
+             * @throws {ArgumentError} If the specified field of view is out of range.
              */
-            this.fieldOfView = 45;
-        };
+            fieldOfView: {
+                get: function () {
+                    return this._fieldOfView;
+                },
+                set: function (value) {
+                    if (value <= 0 || value => 180) {
+                        throw new ArgumentError(
+                            Logger.logMessage(Logger.LEVEL_SEVERE, "Camera", "setFieldOfView", "Invalid field of view")
+                        );
+                    }
+                    this._fieldOfView = value;
+                }
+            }
+        });
 
         /**
          * Indicates whether the components of this object are equal to those of a specified object.