Introduce PerspectiveView.fovx

docs/api/perspective-view.md

 
 Aspect ratio of the viewing frustum.
 
+### fovx
+
+`view.fovx: number, read-only`
+
+Horizontal field-of-view of the viewing frustum, measured in radians.
+
+*Since:* 0.3.0
+
 ### fovy
 
 `view.fovy: number, read-only`

src/geometry/view.ts

     /** A 4x4 matrix that projects the viewer space into the clip space, i.e., [-1,1]^3 */
     private readonly _projectionMatrix: SpeedyMatrix;
 
+    /** Tangent of the half of the horizontal field-of-view */
+    private readonly _tanOfHalfFovx: number;
+
     /** Tangent of the half of the vertical field-of-view */
     private readonly _tanOfHalfFovy: number;
 
             throw new IllegalArgumentError(`View expects near < far (found near = ${this._near} and far = ${this._far})`);
 
         this._aspect = screenSize.width / screenSize.height;
+        this._tanOfHalfFovx = intrinsics[U0] / intrinsics[FX];
         this._tanOfHalfFovy = intrinsics[V0] / intrinsics[FY];
         this._projectionMatrix = PerspectiveView._computeProjectionMatrix(intrinsics, this._near, this._far);
     }
     }
 
     /**
+     * Horizontal field-of-view of the frustum, measured in radians
+     */
+    get fovx(): number
+    {
+        return 2 * Math.atan(this._tanOfHalfFovx);
+    }
+
+    /**
      * Vertical field-of-view of the frustum, measured in radians
      */
     get fovy(): number