glium 0.3.3

High-level and safe OpenGL wrapper.
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extern crate glutin;

#[macro_use]
extern crate glium;

use glium::Surface;

mod support;

fn main() {
    use glium::DisplayBuild;

    // building the display, ie. the main object
    let display = glutin::WindowBuilder::new()
        .build_glium()
        .unwrap();

    // building the vertex buffer, which contains all the vertices that we will draw
    let vertex_buffer = {
        #[derive(Copy, Clone)]
        struct Vertex {
            position: [f32; 2],
        }

        implement_vertex!(Vertex, position);

        glium::VertexBuffer::new(&display, 
            vec![
                Vertex { position: [-0.5, -0.5] },
                Vertex { position: [ 0.0,  0.5] },
                Vertex { position: [ 0.5, -0.5] },
            ]
        )
    };

    // building the index buffer
    let index_buffer = glium::IndexBuffer::new(&display,
        glium::index::Patches(vec![0u16, 1, 2], 3));

    // compiling shaders and linking them together
    let program = glium::Program::new(&display,
        glium::program::SourceCode {
            vertex_shader: "
                #version 140

                in vec2 position;

                void main() {
                    gl_Position = vec4(position, 0.0, 1.0);
                }
            ",
            fragment_shader: "
                #version 140

                in vec3 color;
                out vec4 f_color;

                void main() {
                    f_color = vec4(color, 1.0);
                }
            ",
            geometry_shader: Some("
                #version 330

                uniform mat4 matrix;

                layout(triangles) in;
                layout(triangle_strip, max_vertices=3) out;

                out vec3 color;

                float rand(vec2 co) {
                    return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
                }

                void main() {
                    vec3 all_color = vec3(
                        rand(gl_in[0].gl_Position.xy + gl_in[1].gl_Position.yz),
                        rand(gl_in[1].gl_Position.yx + gl_in[2].gl_Position.zx),
                        rand(gl_in[0].gl_Position.xz + gl_in[2].gl_Position.zy)
                    );

                    gl_Position = matrix * gl_in[0].gl_Position;
                    color = all_color;
                    EmitVertex();

                    gl_Position = matrix * gl_in[1].gl_Position;
                    color = all_color;
                    EmitVertex();

                    gl_Position = matrix * gl_in[2].gl_Position;
                    color = all_color;
                    EmitVertex();
                }
            "),
            tessellation_control_shader: Some("
                #version 400

                layout(vertices = 3) out;

                uniform int tess_level = 5;

                void main() {
                    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;

                    gl_TessLevelOuter[0] = tess_level;
                    gl_TessLevelOuter[1] = tess_level;
                    gl_TessLevelOuter[2] = tess_level;
                    gl_TessLevelInner[0] = tess_level;
                }
            "),
            tessellation_evaluation_shader: Some("
                #version 400

                layout(triangles, equal_spacing) in;

                void main() {
                    vec3 position = vec3(gl_TessCoord.x) * gl_in[0].gl_Position.xyz +
                                    vec3(gl_TessCoord.y) * gl_in[1].gl_Position.xyz +
                                    vec3(gl_TessCoord.z) * gl_in[2].gl_Position.xyz;
                    gl_Position = vec4(position, 1.0);
                }

            "),
        }).unwrap();

    // level of tessellation
    let mut tess_level: i32 = 5;
    println!("The current tessellation level is {} ; use the Up and Down keys to change it", tess_level);
    
    // the main loop
    support::start_loop(|| {
        // building the uniforms
        let uniforms = uniform! {
            matrix: [
                [1.0, 0.0, 0.0, 0.0],
                [0.0, 1.0, 0.0, 0.0],
                [0.0, 0.0, 1.0, 0.0],
                [0.0, 0.0, 0.0, 1.0f32]
            ],
            tess_level: tess_level
        };

        // drawing a frame
        let mut target = display.draw();
        target.clear_color(0.0, 0.0, 0.0, 0.0);
        target.draw(&vertex_buffer, &index_buffer, &program, &uniforms, &std::default::Default::default()).unwrap();
        target.finish();

        // polling and handling the events received by the window
        for event in display.poll_events() {
            match event {
                glutin::Event::Closed => return support::Action::Stop,
                glutin::Event::KeyboardInput(glutin::ElementState::Pressed, _, Some(glutin::VirtualKeyCode::Up)) => {
                    tess_level += 1;
                    println!("New tessellation level: {}", tess_level);
                },
                glutin::Event::KeyboardInput(glutin::ElementState::Pressed, _, Some(glutin::VirtualKeyCode::Down)) => {
                    if tess_level >= 2 {
                        tess_level -= 1;
                        println!("New tessellation level: {}", tess_level);
                    }
                },
                _ => ()
            }
        }

        support::Action::Continue
    });
}