precision mediump float;

​

uniform vec2 mapPos;

uniform vec2 res;

​

in vec2 pos;

out vec4 colour;

​

#define NUM_NOISE_OCTAVES 5

​

// Noise algo from:

// https://www.shadertoy.com/view/4dS3Wd

​

float hash(vec2 p) {vec3 p3 = fract(vec3(p.xyx) * 0.13); p3 += dot(p3, p3.yzx + 3.333); return fract((p3.x + p3.y) * p3.z); }

​

float noise(vec2 x) {

    vec2 i = floor(x);

    vec2 f = fract(x);

​

    // Four corners in 2D of a tile

    float a = hash(i);

    float b = hash(i + vec2(1.0, 0.0));

    float c = hash(i + vec2(0.0, 1.0));

    float d = hash(i + vec2(1.0, 1.0));

​

    // Simple 2D lerp using smoothstep envelope between the values.

    // return vec3(mix(mix(a, b, smoothstep(0.0, 1.0, f.x)),

    //          mix(c, d, smoothstep(0.0, 1.0, f.x)),

    //          smoothstep(0.0, 1.0, f.y)));

​

    // Same code, with the clamps in smoothstep and common subexpressions

    // optimized away.

    vec2 u = f * f * (3.0 - 2.0 * f);

    return mix(a, b, u.x) + (c - a) * u.y * (1.0 - u.x) + (d - b) * u.x * u.y;

}

​

float fbm(vec2 x) {

    float v = 0.0;

    float a = 0.5;

    vec2 shift = vec2(100);

    // Rotate to reduce axial bias

    mat2 rot = mat2(cos(0.5), sin(0.5), -sin(0.5), cos(0.50));

    for (int i = 0; i < NUM_NOISE_OCTAVES; ++i) {

        v += a * noise(x);

        x = rot * x * 2.0 + shift;

        a *= 0.5;

    }

    return v;

}

​

vec4 packHeight(float value) {

    int rgba = floatBitsToInt(value);

    float a = float((rgba & 0xff000000) >> 24) / 255.0;

    float b = float((rgba & 0x00ff0000) >> 16) / 255.0;

    float g = float((rgba & 0x0000ff00) >> 8) / 255.0;

    float r = float(rgba & 0x000000ff) / 255.0;

    a = max(1./255., a);

    return vec4(r, g, b, a);

}

​

float getHeight(vec2 p) {

  p += mapPos;  

  float n = 1.1 * fbm(p * 5.);

  n = pow(n, 2.);

  float d = length(pos - (0.5)) * 2.;

  return clamp(n * (1.3 - d), 0., 1.);

}

​

void main() {

  float d = length(pos - 0.5);

  float h = (1. - step(0.3, d)) * step(0.1, d) * 0.5 + (1. - d) * 0.5;

  // float h = getHeight(pos * res);

  colour = packHeight(h);

}