将一个世界坐标系下的点转换到屏幕坐标系下
camera.getWorldToScreenPoint(point, out);
camera.worldToScreen
public worldToScreen (worldPos: Vec3, out?: Vec3) {
if (!out) { out = new Vec3(); }
if (this._camera) { this._camera.worldToScreen(out, worldPos); }
return out;
}