vec3 srgb_from_rgb(vec3 rgb) {
        vec3 a = vec3(0.055, 0.055, 0.055);
        vec3 ap1 = vec3(1.0, 1.0, 1.0) + a;
        vec3 g = vec3(2.4, 2.4, 2.4);
        vec3 ginv = 1.0 / g;
        vec3 select = step(vec3(0.0031308, 0.0031308, 0.0031308), rgb);
        vec3 lo = rgb * 12.92;
        vec3 hi = ap1 * pow(rgb, ginv) - a;
        return mix(lo, hi, select);
    }

    vec3 rgb_from_srgb(vec3 srgb) {
        vec3 a = vec3(0.055, 0.055, 0.055);
        vec3 ap1 = vec3(1.0, 1.0, 1.0) + a;
        vec3 g = vec3(2.4, 2.4, 2.4);
        vec3 select = step(vec3(0.04045, 0.04045, 0.04045), srgb);
        vec3 lo = srgb / 12.92;
        vec3 hi = pow((srgb + a) / ap1, g);
        return mix(lo, hi, select);
    }

Edit: comparison between non-colourspace-corrected and colourspace-corrected versions of the shadertoy link http://www.screenshotcomparison.com/comparison/134695

    // do some soft coloring based on distance
    d = clamp( 8.0*d/zoo, 0.0, 1.0 );
    d = pow( d, 0.25 );
    vec3 col = vec3( d );

The bottom line is that sRGB is hideously hard to work in. You really want to only use it for storage and only if you really must. It's an optimisation to allow you better range on the low end, at the expense of the high intensity end, to match human colour vision. However, that means using 48bit RGB and that's not a price everyone wants to pay. People who do professional graphics work simply use 32bit floats per colour channel - 128bit RGBA, or even 192bit RGBRaGaBa (separate alpha for each channel) and have workstations with 32 or 64GB of RAM. However, your normal everyday GUI application needs to run on a phone with about 1GB of RAM. Or going back farther, it has to run on an Intel 486 with 16MB of RAM. That kind of explains where the culture of "just treat it as linear, it's not that wrong" came from :) .