CameraTransition: Improve transition capabilities

[gkjohnson]

• Transitioning to Ortho: provide easy way to tilt camera up to top down, retaining the orientation
• Transitioning to Persp: tilt camera down from ortho view if it's not already tilted down too far
• Afford transition while dragging the camera
  • ie rotating the camera from ortho auto-transitions to perspective

[gkjohnson]

When calculating the top down orientation of the ortho camera, ensure the same screen space position of the pivot point. Though calculating the top-orientation of the offset position in that case is not necessarily trivial. Requiring a centered position is easiest.

[gkjohnson]

if ( ! manager.animating ) {

	// Force the fixed point to be in the camera center
	raycaster.ray.direction.set( 0, 0, - 1 ).transformDirection( manager.camera.matrixWorld );
	raycaster.ray.origin.setFromMatrixPosition( manager.camera.matrixWorld );
	const hit = raycaster.intersectObject( scene )[ 0 ];
	if ( hit ) {

		manager.fixedPoint.copy( hit.point );
		manager.syncCameras();

	} else {

		controls.getPivotPoint( manager.fixedPoint );
		manager.syncCameras();

	}

	if ( targetCamera.isOrthographicCamera ) {

		targetCamera.updateMatrixWorld();
		downVector.set( 0, - 1, 0 );	

		// transition the camera view to the top down while retaining same general pointing direction
		const angle = downVector.angleTo( raycaster.ray.direction );
		axis.crossVectors( downVector, raycaster.ray.direction );
		quat.setFromAxisAngle( axis, - angle ).normalize()	;

		makeRotateAroundPoint( manager.fixedPoint, quat, matrix );
		targetCamera.matrixWorld.premultiply( matrix );
		targetCamera.matrixWorld.decompose(
			targetCamera.position,
			targetCamera.quaternion,
			targetCamera.scale,
		);

	} else {

		targetCamera.updateMatrixWorld();
		downVector.set( 0, - 1, 0 );	

		// tilt the perspective down slightly
		let angle = downVector.angleTo( raycaster.ray.direction );
		angle = Math.max( 65 * MathUtils.DEG2RAD - angle, 0 );

		axis.set( 1, 0, 0 ).transformDirection( targetCamera.matrixWorld );
		quat.setFromAxisAngle( axis, angle ).normalize()	;

		makeRotateAroundPoint( manager.fixedPoint, quat, matrix );
		targetCamera.matrixWorld.premultiply( matrix );
		targetCamera.matrixWorld.decompose(
			targetCamera.position,
			targetCamera.quaternion,
			targetCamera.scale,
		);

	}

}

controls.adjustCamera( manager.perspectiveCamera );
controls.adjustCamera( manager.orthographicCamera );