Add a window camera getter

[antonylsg]

Hello,

I suggest to add a handle to the window camera.

I came across a situation where I needed to apply a global rotation to all objects of the scene. I found it useful to apply the inverse rotation to the camera instead.

Here is a minimal example how I use it:

use kiss3d::camera::Camera;
use kiss3d::light::Light;
use kiss3d::window::Window;
use nalgebra::{UnitQuaternion, Vector3};

fn main() {
    let mut window = Window::new("Kiss3d: cube");
    let mut cube = window.add_cube(1.0, 1.0, 1.0);

    cube.set_color(1.0, 0.0, 0.0);

    window.set_light(Light::StickToCamera);

    let rotation = UnitQuaternion::from_axis_angle(&Vector3::y_axis(), -0.014);

    while window.render() {
        let mut camera = window.camera().borrow_mut();

        let at = rotation * camera.at();
        let eye = rotation * camera.eye();

        camera.look_at(eye, at);
    }
}

Edit:

We could alternativly define:

use std::cell::Ref;
use std::cell::RefMut;

pub fn camera(&self) -> Ref<'_, ArcBall> {
    self.camera.borrow()
}

pub fn camera_mut(&self) -> RefMut<'_, ArcBall> {
    self.camera.borrow_mut()
}

[alvinhochun]

I believe the canonical way to do it is to construct your own camera or use one of kiss3d::camera::* and pass it to Window::render_with_camera instead of calling Window::render. Alternatively, you can create a type and have it implement kiss3d::window::State which allows you to return your own camera in State::cameras_and_effect_and_renderer, then use Window::render_loop to start the rendering.