three.js/examples/js/utils/CameraUtils.js

( function () {

	const _va = /*@__PURE__*/new THREE.Vector3(),
		// from pe to pa
		_vb = /*@__PURE__*/new THREE.Vector3(),
		// from pe to pb
		_vc = /*@__PURE__*/new THREE.Vector3(),
		// from pe to pc
		_vr = /*@__PURE__*/new THREE.Vector3(),
		// right axis of screen
		_vu = /*@__PURE__*/new THREE.Vector3(),
		// up axis of screen
		_vn = /*@__PURE__*/new THREE.Vector3(),
		// normal vector of screen
		_vec = /*@__PURE__*/new THREE.Vector3(),
		// temporary vector
		_quat = /*@__PURE__*/new THREE.Quaternion(); // temporary quaternion


	class CameraUtils {

		/** Set a PerspectiveCamera's projectionMatrix and quaternion
   * to exactly frame the corners of an arbitrary rectangle.
   * NOTE: This function ignores the standard parameters;
   * do not call updateProjectionMatrix() after this!
   * @param {Vector3} bottomLeftCorner
   * @param {Vector3} bottomRightCorner
   * @param {Vector3} topLeftCorner
   * @param {boolean} estimateViewFrustum */
		static frameCorners( camera, bottomLeftCorner, bottomRightCorner, topLeftCorner, estimateViewFrustum = false ) {

			const pa = bottomLeftCorner,
				pb = bottomRightCorner,
				pc = topLeftCorner;
			const pe = camera.position; // eye position

			const n = camera.near; // distance of near clipping plane

			const f = camera.far; //distance of far clipping plane

			_vr.copy( pb ).sub( pa ).normalize();

			_vu.copy( pc ).sub( pa ).normalize();

			_vn.crossVectors( _vr, _vu ).normalize();

			_va.copy( pa ).sub( pe ); // from pe to pa


			_vb.copy( pb ).sub( pe ); // from pe to pb


			_vc.copy( pc ).sub( pe ); // from pe to pc


			const d = - _va.dot( _vn ); // distance from eye to screen

			const l = _vr.dot( _va ) * n / d; // distance to left screen edge

			const r = _vr.dot( _vb ) * n / d; // distance to right screen edge

			const b = _vu.dot( _va ) * n / d; // distance to bottom screen edge

			const t = _vu.dot( _vc ) * n / d; // distance to top screen edge
			// Set the camera rotation to match the focal plane to the corners' plane

			_quat.setFromUnitVectors( _vec.set( 0, 1, 0 ), _vu );

			camera.quaternion.setFromUnitVectors( _vec.set( 0, 0, 1 ).applyQuaternion( _quat ), _vn ).multiply( _quat ); // Set the off-axis projection matrix to match the corners

			camera.projectionMatrix.set( 2.0 * n / ( r - l ), 0.0, ( r + l ) / ( r - l ), 0.0, 0.0, 2.0 * n / ( t - b ), ( t + b ) / ( t - b ), 0.0, 0.0, 0.0, ( f + n ) / ( n - f ), 2.0 * f * n / ( n - f ), 0.0, 0.0, - 1.0, 0.0 );
			camera.projectionMatrixInverse.copy( camera.projectionMatrix ).invert(); // FoV estimation to fix frustum culling

			if ( estimateViewFrustum ) {

				// Set fieldOfView to a conservative estimate
				// to make frustum tall/wide enough to encompass it
				camera.fov = THREE.MathUtils.RAD2DEG / Math.min( 1.0, camera.aspect ) * Math.atan( ( _vec.copy( pb ).sub( pa ).length() + _vec.copy( pc ).sub( pa ).length() ) / _va.length() );

			}

		}

	}

	THREE.CameraUtils = CameraUtils;

} )();