Google Web Mercator pixel coordinates to latitude & longitude, in GLSL / https://fredriknoren.github.io/glsl-repl/

pixel_to_lat_lng.glsl

#version 300 es
precision highp float;
out vec2 res;

#define TILE_SIZE 256u
#define PI 3.141592653589793
#define EARTH_RADIUS 6378137.0

vec2 webMercatorToLatLng(vec2 pixelCoord, uint zoomLevel) {
    float initialResolution = 2.0 * PI * EARTH_RADIUS / float(TILE_SIZE);
    float originShift = PI * EARTH_RADIUS;

    float res = initialResolution / float(1 << zoomLevel);
    float mx = (pixelCoord.x * res) - originShift;
    float my = -((pixelCoord.y * res) - originShift);

    float lon = degrees(mx / EARTH_RADIUS);
    float lat = degrees(my / EARTH_RADIUS);
    lat = degrees(2.0 * atan(exp(radians(lat)))) - 90.0;

    return vec2(lat, lon);
}

void main() {
  vec2 pixelCoordinate = vec2(131, 190);
  res = webMercatorToLatLng(pixelCoordinate, uint(1));
}