Emulate the cover css property in a shader

GSLS_Emulate background-fit:cover

// An implementation of CSS `background-size: cover`
// using http://stackoverflow.com/a/6565988
vec2 s = uScreenSize; // Screen
vec2 i = uBGSize; // Image
float rs = s.x / s.y;
float ri = i.x / i.y;
vec2 new = rs < ri ? vec2(i.x * s.y / i.y, s.y) : vec2(s.x, i.y * s.x / i.x);
vec2 offset = (rs < ri ? vec2((new.x - s.x) / 2.0, 0.0) : vec2(0.0, (new.y - s.y) / 2.0)) / new;
vec2 uv = vTexCoord * s / new + offset;
gl_FragColor = texture2D(uBGTex, uv);

// 07.01.2024 - Naples Jesper
vec2 background(vec2 res, vec2 size, vec2 uv) {
  float resRatio = res.x / res.y;
  float imageRatio = size.x / size.y;

  vec2 newSize = resRatio < imageRatio
      ? vec2(size.x * (res.y / size.y), res.y)
      : vec2(res.x, size.y * (res.x / size.x));
  vec2 newOffset = (resRatio < imageRatio
      ? vec2((newSize.x - res.x) / 2.0, 0.0)
      : vec2(0.0, (newSize.y - res.y) / 2.0)) / newSize;

  return uv * res / newSize + newOffset;
}



// WORKING
vec2 uvCover(vec2 uv, vec2 size, vec2 resolution) {
    vec2 coverUv = uv;
    vec2 s = resolution; // Screen
    vec2 i = size; // Image

    float rs = s.x / s.y;
    float ri = i.x / i.y;
    vec2 new = rs < ri ? vec2(i.x * s.y / i.y, s.y) : vec2(s.x, i.y * s.x / i.x);
    vec2 offset = (rs < ri ? vec2((new.x - s.x) / 2.0, 0.0) : vec2(0.0, (new.y - s.y) / 2.0)) / new;
    
    coverUv = coverUv * s / new + offset;

    return coverUv;
}

// NOT TESTED
vec2(vec2 screenSize, vec2 bgSize, vec2 textCoord) {
    vec2 s = screenSize; // Screen
    vec2 i = bgSize; // Image
    float rs = s.x / s.y;
    float ri = i.x / i.y;
    vec2 new = rs < ri ? vec2(i.x * s.y / i.y, s.y) : vec2(s.x, i.y * s.x / i.x);
    vec2 offset = (rs < ri ? vec2((new.x - s.x) / 2.0, 0.0) : vec2(0.0, (new.y - s.y) / 2.0)) / new;
    vec2 uv = textCoord * s / new + offset;
    return uv;
}