@group(0) @binding(0) var<uniform> mvp_matrix: mat4x4<f32>;

struct VertexOutput {
    @builtin(position) position: vec4<f32>,
    @location(0) color: vec4<f32>,
};

struct FragmentOutput {
    @location(0) pixel_color: vec4<f32>
};

@vertex fn vertex_main(
    @builtin(vertex_index) index: u32
) -> VertexOutput {
    let color = array<vec3<f32>, 3>(
        vec3<f32>(1.0, 0.0, 0.0),
        vec3<f32>(0.0, 1.0, 0.0),
        vec3<f32>(0.0, 0.0, 1.0),
    );
    let pos = array<vec2<f32>, 9>(
        vec2<f32>(-1.0,  0.5 + 0.25),
        vec2<f32>(-1.5, -0.5 + 0.25),
        vec2<f32>(-0.5, -0.5 + 0.25),

        vec2<f32>( 0.0,  0.5 - 0.25),
        vec2<f32>(-0.5, -0.5 - 0.25),
        vec2<f32>( 0.5, -0.5 - 0.25),

        vec2<f32>( 1.0,  0.5),
        vec2<f32>( 0.5, -0.5),
        vec2<f32>( 1.5, -0.5),
    );

    var out: VertexOutput;
    out.position = vec4<f32>(pos[index], 0.0, 1.0) * mvp_matrix;
    out.color    = vec4<f32>(color[index / 3], 1.0);
    return out;
}

@fragment fn frag_main(in: VertexOutput) -> FragmentOutput {
    var out: FragmentOutput;
    out.pixel_color = in.color;
    return out;
}