Animating our triangle

https://github.com/glium/glium/blob/master/book/tuto-03-animated-triangle.md

이전 내용에서 그린 삼각형을 움직임
화면 내용을 변경하려면 기존 내용을 덮어씀

naive approach

animation step을 나타내는 t를 생성하고 매루프 마다 업데이트

let mut t: f32 = -0.5;
event_loop.run(move |event, _, control_flow| {

    match event {
        glutin::event::Event::WindowEvent { event, .. } => match event {
            glutin::event::WindowEvent::CloseRequested => {
                *control_flow = glutin::event_loop::ControlFlow::Exit;
                return;
            },
            _ => return,
        },
        glutin::event::Event::NewEvents(cause) => match cause {
            glutin::event::StartCause::ResumeTimeReached { .. } => (),
            glutin::event::StartCause::Init => (),
            _ => return,
        },
        _ => return,
    }

    let next_frame_time = std::time::Instant::now() +
            std::time::Duration::from_nanos(16_666_667);
    *control_flow = glutin::event_loop::ControlFlow::WaitUntil(next_frame_time);

    // we update `t`
    t += 0.0002;
    if t > 0.5 {
        t = -0.5;
    }
    
    let vertex1 = Vertex { position: [-0.5 + t, -0.5] };
    let vertex2 = Vertex { position: [ 0.0 + t,  0.5] };
    let vertex3 = Vertex { position: [ 0.5 + t, -0.25] };
    let shape = vec![vertex1, vertex2, vertex3];

    let vertex_buffer = glium::VertexBuffer::new(&display, &shape).unwrap();

    let mut target = display.draw();
    target.clear_color(0.0, 0.0, 1.0, 1.0);
    target.draw(&vertex_buffer, &indices, &program, &glium::uniforms::EmptyUniforms,
            &Default::default()).unwrap();
    target.finish().unwrap();
});

---

Uniforms

vertex shader를 활용
vertex shader code 수정

let vertex_shader_src = r#"
    #version 140

    in vec2 position;

    uniform float t;

    void main() {
        vec2 pos = position;
        pos.x += t;
        gl_Position = vec4(pos, 0.0, 1.0);
    }
"#;

rendering code 수정

let vertex1 = Vertex { position: [-0.5, -0.5] };
let vertex2 = Vertex { position: [ 0.0,  0.5] };
let vertex3 = Vertex { position: [ 0.5, -0.25] };
let shape = vec![vertex1, vertex2, vertex3];

let vertex_buffer = glium::VertexBuffer::new(&display, &shape).unwrap();
let mut t: f32 = -0.5;
event_loop.run(move |event, _, control_flow| {

    match event {
        glutin::event::Event::WindowEvent { event, .. } => match event {
            glutin::event::WindowEvent::CloseRequested => {
                *control_flow = glutin::event_loop::ControlFlow::Exit;
                return;
            },
            _ => return,
        },
        glutin::event::Event::NewEvents(cause) => match cause {
            glutin::event::StartCause::ResumeTimeReached { .. } => (),
            glutin::event::StartCause::Init => (),
            _ => return,
        },
        _ => return,
    }

    let next_frame_time = std::time::Instant::now() +
        std::time::Duration::from_nanos(16_666_667);
    *control_flow = glutin::event_loop::ControlFlow::WaitUntil(next_frame_time);

    // we update `t`
    t += 0.0002;
    if t > 0.5 {
        t = -0.5;
    }

    let mut target = display.draw();
    target.clear_color(0.0, 0.0, 1.0, 1.0);
    target.draw(&vertex_buffer, &indices, &program, &glium::uniforms::EmptyUniforms,
            &Default::default()).unwrap();
    target.finish().unwrap();
});