-- Auroras by nimitz 2017 (twitter: @stormoid)
-- License Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
-- Converted from ShaderToy to live-wallpaper system

effect = nil

function _create()
    local fxSrc = [[
#define time uTime

mat2 mm2(in float a){float c = cos(a), s = sin(a);return mat2(c,s,-s,c);}
mat2 m2 = mat2(0.95534, 0.29552, -0.29552, 0.95534);
float tri(in float x){return clamp(abs(fract(x)-.5),0.01,0.49);}
vec2 tri2(in vec2 p){return vec2(tri(p.x)+tri(p.y),tri(p.y+tri(p.x)));}

float triNoise2d(in vec2 p, float spd)
{
    float z=1.8;
    float z2=2.5;
    float rz = 0.;
    p *= mm2(p.x*0.06);
    vec2 bp = p;
    for (float i=0.; i<5.; i++ )
    {
        vec2 dg = tri2(bp*1.85)*.75;
        dg *= mm2(time*spd);
        p -= dg/z2;

        bp *= 1.3;
        z2 *= .45;
        z *= .42;
        p *= 1.21 + (rz-1.0)*.02;

        rz += tri(p.x+tri(p.y))*z;
        p*= -m2;
    }
    return clamp(1./pow(rz*29., 1.3),0.,.55);
}

float hash21(in vec2 n){ return fract(sin(dot(n, vec2(12.9898, 4.1414))) * 43758.5453); }

vec4 aurora(vec3 ro, vec3 rd)
{
    vec4 col = vec4(0);
    vec4 avgCol = vec4(0);

    for(float i=0.;i<50.;i++)
    {
        float of = 0.006*hash21(gl_FragCoord.xy)*smoothstep(0.,15., i);
        float pt = ((.8+pow(i,1.4)*.002)-ro.y)/(rd.y*2.+0.4);
        pt -= of;
        vec3 bpos = ro + pt*rd;
        vec2 p = bpos.zx;
        float rzt = triNoise2d(p, 0.06);
        vec4 col2 = vec4(0,0,0, rzt);
        col2.rgb = (sin(1.-vec3(2.15,-.5, 1.2)+i*0.043)*0.5+0.5)*rzt;
        avgCol =  mix(avgCol, col2, .5);
        col += avgCol*exp2(-i*0.065 - 2.5)*smoothstep(0.,5., i);
    }

    col *= (clamp(rd.y*15.+.4,0.,1.));

    return col*1.8;
}

//-------------------Background and Stars--------------------

vec3 nmzHash33(vec3 q)
{
    uvec3 p = uvec3(ivec3(q));
    p = p*uvec3(374761393U, 1103515245U, 668265263U) + p.zxy + p.yzx;
    p = p.yzx*(p.zxy^(p >> 3U));
    return vec3(p^(p >> 16U))*(1.0/vec3(0xffffffffU));
}

vec3 stars(in vec3 p)
{
    vec3 c = vec3(0.);
    float res = uDesktopSize.x*1.;

    for (float i=0.;i<4.;i++)
    {
        vec3 q = fract(p*(.15*res))-0.5;
        vec3 id = floor(p*(.15*res));
        vec2 rn = nmzHash33(id).xy;
        float c2 = 1.-smoothstep(0.,.6,length(q));
        c2 *= step(rn.x,.0005+i*i*0.001);
        c += c2*(mix(vec3(1.0,0.49,0.1),vec3(0.75,0.9,1.),rn.y)*0.1+0.9);
        p *= 1.3;
    }
    return c*c*.8;
}

vec3 bg(in vec3 rd)
{
    float sd = dot(normalize(vec3(-0.5, -0.6, 0.9)), rd)*0.5+0.5;
    sd = pow(sd, 5.);
    vec3 col = mix(vec3(0.05,0.1,0.2), vec3(0.1,0.05,0.2), sd);
    return col*.63;
}
//-----------------------------------------------------------

void main()
{
    vec2 fragCoord = (vPosition * 0.5 + 0.5) * uDesktopSize;

    vec2 q = fragCoord.xy / uDesktopSize.xy;
    vec2 p = q - 0.5;
    p.x *= uDesktopSize.x / uDesktopSize.y;

    vec3 ro = vec3(0,0,-6.7);
    vec3 rd = normalize(vec3(p,1.3));
    vec2 mo = uMouse.xy / uDesktopSize.xy-.5;
    mo = (mo==vec2(-.5))?mo=vec2(-0.1,0.1):mo;
    mo.x *= uDesktopSize.x / uDesktopSize.y;
    rd.yz *= mm2(mo.y);
    rd.xz *= mm2(mo.x + sin(time*0.05)*0.2);

    vec3 col = vec3(0.);
    vec3 brd = rd;
    float fade = smoothstep(0.,0.01,abs(brd.y))*0.1+0.9;

    col = bg(rd)*fade;

    if (rd.y > 0.){
        vec4 aur = smoothstep(0.,1.5,aurora(ro,rd))*fade;
        col += stars(rd);
        col = col*(1.-aur.a) + aur.rgb;
    }
    else //Reflections
    {
        rd.y = abs(rd.y);
        col = bg(rd)*fade*0.6;
        vec4 aur = smoothstep(0.0,2.5,aurora(ro,rd));
        col += stars(rd)*0.1;
        col = col*(1.-aur.a) + aur.rgb;
        vec3 pos = ro + ((0.5-ro.y)/rd.y)*rd;
        float nz2 = triNoise2d(pos.xz*vec2(.5,.7), 0.);
        col += mix(vec3(0.2,0.25,0.5)*0.08,vec3(0.3,0.3,0.5)*0.7, nz2*0.4);
    }

    FragColor = vec4(col, 1.);
}
    ]]
    effect = Effect.new(fxSrc)
end

function _update(dt)
end

function _render()
    gl.Clear(0, 0, 0, 1.0)
    effect:Render()
end