#version 320 es

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

precision highp float;

layout(location = 0) out vec4 fragColor;

layout(location = 0) uniform float a;

// For a given incident vector I and surface normal N reflect returns the reflection direction calculated as I - 2.0 * dot(N, I) * N.
void main() {
    // To get [0.0, 1.0] as the output, choose [0.6, 0.8] as N, and solve for I.
    // Since the reflection is symmetric:
    // I’ = reflect(I)
    // I’ = I - 2 dot(N, I) N
    // I = I’ - 2 dot(N, I’) N
    // N = [0.6, 0.8]
    // I’ = [0, 1]
    // I = [0, 1] - 2 * 0.8 [0.6, 0.8]
    // I = [-0.96, -0.28]
    fragColor = vec4(
        reflect(vec2(a * -0.96, -0.28), vec2(0.6, 0.8))[0],
        reflect(vec2(a * -0.96, -0.28), vec2(0.6, 0.8))[1],
        0.0,
        1.0
    );
}