问题
I have a fixed-position, perspective camera that rotates around all 3 axes via keyboard input. At random intervals, independent of user input, I need to place objects within the camera's field of view no matter what direction the camera is looking. The objects will also need to be offset specific x and y distances from the center of the camera's fov and offset a specific z distance from the camera's position. I cannot use camera.addChild because once the object is added I need to move the object via tweening independent of the camera's movements.
How can this be done?
回答1:
You want to transform a point from camera space to world space.
In the camera's coordinate system, the camera is located at the origin, and is looking down its negative z-axis.
Place the object in front of the camera (in the camera's coordinate system).
object.position.set( x, y, - z ); // z is the distance in front of the camera, and is positive
Now, transform the object's position from camera space to world space:
object.position.applyMatrix4( camera.matrixWorld );
three.js r.69
来源：https://stackoverflow.com/questions/26910120/three-js-place-an-object-in-rotating-cameras-fov