[vert.glsl]

#version 120

uniform float u_Time;

attribute vec2 in_Position;

varying vec4 pass_Position;
varying vec3 water[4];
varying vec3 fire[4];

float mod289(float x)
{
    return x - floor(x * (1.0 / 289.0)) * 289.0;
}

void main(void)
{
    mat3 r = mat3(0.36, 0.48, -0.8, -0.8, 0.60, 0.0, 0.48, 0.64, 0.60);
    vec3 p_pos = r * vec3(in_Position * vec2(16.0, 9.0), 0.0);
    vec3 p_time = r * vec3(0.0, 0.0, u_Time * 2.0);

    /* Noise sampling points for water */
    water[0] = p_pos / 2.0 + p_time;
    water[1] = p_pos / 4.0 + p_time;
    water[2] = p_pos / 8.0 + p_time;
    water[3] = p_pos / 16.0 + p_time;

    /* Noise sampling points for fire */
    p_pos = 16.0 * p_pos - r * vec3(0.0, mod289(u_Time) * 128.0, 0.0);
    fire[0] = p_pos / 2.0 + p_time * 2.0;
    fire[1] = p_pos / 4.0 + p_time * 1.5;
    fire[2] = p_pos / 8.0 + p_time;
    fire[3] = p_pos / 16.0 + p_time;

    /* Pass rotated screen coordinates */
    pass_Position.xy = in_Position;
    mat2 rot = mat2(cos(u_Time), sin(u_Time), -sin(u_Time), cos(u_Time));
    pass_Position.zw = rot * in_Position;

    gl_Position = vec4(in_Position, 0.0, 1.0);
}

[frag.glsl]

#version 120

uniform float u_Time;

varying vec4 pass_Position;
varying vec3 water[4];
varying vec3 fire[4];

vec4 mod289(vec4 x)
{
    return x - floor(x * (1.0 / 289.0)) * 289.0;
}

vec4 perm(vec4 x)
{
    return mod289(((x * 34.0) + 1.0) * x);
}

float noise3d(vec3 p)
{
    vec3 a = floor(p);
    vec3 d = p - a;
    d = d * d * (3.0 - 2.0 * d);

    vec4 b = a.xxyy + vec4(0.0, 1.0, 0.0, 1.0);
    vec4 k1 = perm(b.xyxy);
    vec4 k2 = perm(k1.xyxy + b.zzww);

    vec4 c = k2 + a.zzzz;
    vec4 k3 = perm(c);
    vec4 k4 = perm(c + 1.0);

    vec4 o1 = fract(k3 * (1.0 / 41.0));
    vec4 o2 = fract(k4 * (1.0 / 41.0));

    vec4 o3 = o2 * d.z + o1 * (1.0 - d.z);
    vec2 o4 = o3.yw * d.x + o3.xz * (1.0 - d.x);

    return o4.y * d.y + o4.x * (1.0 - d.y);
}

void main(void)
{
    /* Dither the transition between water and fire */
    float test = pass_Position.z * pass_Position.w + 1.5 * sin(u_Time);
    vec2 d = vec2(16.0, 9.0) * pass_Position.xy;
    test += 0.5 * (length(fract(d) - 0.5) - length(fract(d + 0.5) - 0.5));

    /* Compute 4 octaves of noise */
    vec3 points[4] = (test > 0.0) ? fire : water;
    vec4 n = vec4(noise3d(points[0]),
                  noise3d(points[1]),
                  noise3d(points[2]),
                  noise3d(points[3]));

    vec4 color;

    if (test > 0.0)
    {
        /* Use noise results for fire */
        float p = dot(n, vec4(0.125, 0.125, 0.25, 0.5));

        /* Fade to black on top of screen */
        p -= pass_Position.y * 0.8 + 0.25;
        p = max(p, 0.0);
        p = min(p, 1.0);

        float q = p * p * (3.0 - 2.0 * p);
        float r = q * q * (3.0 - 2.0 * q);
        color = vec4(min(q * 2.0, 1.0),
                     max(r * 1.5 - 0.5, 0.0),
                     max(q * 8.0 - 7.3, 0.0),
                     1.0);
    }
    else
    {
        /* Use noise results for water */
        float p = dot(abs(2.0 * n - 1.0),
                      vec4(0.5, 0.25, 0.125, 0.125));
        float q = sqrt(p);

        color = vec4(1.0 - q,
                     1.0 - 0.5 * q,
                     1.0,
                     1.0);
    }

    gl_FragColor = color;
}

[vert.hlsl]

float mod289(float x)
{
    return x - floor(x * (1.0 / 289.0)) * 289.0;
}

void main(float2 in_Position : POSITION,
          uniform float u_Time,
          out float4 out_Position : POSITION,
          out float4 pass_Position : TEXCOORD0,
          out float3 water[4] : TEXCOORD1,
          out float3 fire[4] : TEXCOORD5)
{
    float3x3 r = float3x3(0.36, 0.48, -0.8, -0.8, 0.60, 0.0, 0.48, 0.64, 0.60);
    float3 p_pos = mul(r, float3(in_Position * float2(16.0, 9.0), 0.0));
    float3 p_time = mul(r, float3(0.0, 0.0, u_Time * 2.0));

    /* Noise sampling points for water */
    water[0] = p_pos / 2.0 + p_time;
    water[1] = p_pos / 4.0 + p_time;
    water[2] = p_pos / 8.0 + p_time;
    water[3] = p_pos / 16.0 + p_time;

    /* Noise sampling points for fire */
    p_pos = 16.0 * p_pos - mul(r, float3(0.0, mod289(u_Time) * 128.0, 0.0));
    fire[0] = p_pos / 2.0 + p_time * 2.0;
    fire[1] = p_pos / 4.0 + p_time * 1.5;
    fire[2] = p_pos / 8.0 + p_time;
    fire[3] = p_pos / 16.0 + p_time;

    /* Pass rotated screen coordinates */
    pass_Position.xy = in_Position;
    float2x2 rot = float2x2(cos(u_Time), sin(u_Time), -sin(u_Time), cos(u_Time));
    pass_Position.zw = mul(rot, in_Position);

    out_Position = float4(in_Position, 0.0, 1.0);
}

[frag.hlsl]

float4 mod289(float4 x)
{
    return x - floor(x * (1.0 / 289.0)) * 289.0;
}

float4 perm(float4 x)
{
    return mod289(((x * 34.0) + 1.0) * x);
}

float noise3d(float3 p)
{
    float3 a = floor(p);
    float3 d = p - a;
    d = d * d * (3.0 - 2.0 * d);

    float4 b = a.xxyy + float4(0.0, 1.0, 0.0, 1.0);
    float4 k1 = perm(b.xyxy);
    float4 k2 = perm(k1.xyxy + b.zzww);

    float4 c = k2 + a.zzzz;
    float4 k3 = perm(c);
    float4 k4 = perm(c + 1.0);

    float4 o1 = frac(k3 * (1.0 / 41.0));
    float4 o2 = frac(k4 * (1.0 / 41.0));

    float4 o3 = o2 * d.z + o1 * (1.0 - d.z);
    float2 o4 = o3.yw * d.x + o3.xz * (1.0 - d.x);

    return o4.y * d.y + o4.x * (1.0 - d.y);
}

void main(in float4 pass_Position : TEXCOORD0,
          in float3 water[4] : TEXCOORD1,
          in float3 fire[4] : TEXCOORD5,
          uniform float u_Time,
          out float4 out_FragColor : COLOR)
{
    /* Dither the transition between water and fire */
    float test = pass_Position.z * pass_Position.w + 1.5 * sin(u_Time);
    float2 d = float2(16.0, 9.0) * pass_Position.xy;
    test += 0.5 * (length(frac(d) - 0.5) - length(frac(d + 0.5) - 0.5));

    float3 points[4];
    points[0] = (test > 0.0) ? fire[0] : water[0];
    points[1] = (test > 0.0) ? fire[1] : water[1];
    points[2] = (test > 0.0) ? fire[2] : water[2];
    points[3] = (test > 0.0) ? fire[3] : water[3];

    /* Compute 4 octaves of noise */
    float4 n = float4(noise3d(points[0]),
                      noise3d(points[1]),
                      noise3d(points[2]),
                      noise3d(points[3]));

    float4 color;

    if (test > 0.0)
    {
        /* Use noise results for fire */
        float p = dot(n, float4(0.125, 0.125, 0.25, 0.5));

        /* Fade to black on top of screen */
        p -= pass_Position.y * 0.8 + 0.25;
        p = max(p, 0.0);
        p = min(p, 1.0);

        float q = p * p * (3.0 - 2.0 * p);
        float r = q * q * (3.0 - 2.0 * q);
        color = float4(min(q * 2.0, 1.0),
                       max(r * 1.5 - 0.5, 0.0),
                       max(q * 8.0 - 7.3, 0.0),
                       1.0);
    }
    else
    {
        /* Use noise results for water */
        float p = dot(abs(2.0 * n - 1.0),
                      float4(0.5, 0.25, 0.125, 0.125));
        float q = sqrt(p);

        color = float4(1.0 - q,
                       1.0 - 0.5 * q,
                       1.0,
                       1.0);
    }

    out_FragColor = color;
}