Shader "Explorer/Mandelbrot"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        // first two numbers are center of area, second two - size of area
        _Area("Area", vector) = (0, 0, 4 ,4)
        _Angle("Angle", range(-3.1415, 3.1415)) = 0
        _MaxIter("Max Iterations", range(0, 555)) = 255
        _Speed("Speed", range(0, 1)) = 0.1
        _EscapeRadius("EscapeRadius", range(2, 2000)) = 255

        _SpectrumTexture("SpectrumTexture", 2D) = "white" {}
        _SpectrumSize("SpectrumSize", float) = 16

        _ThemeTexture("ThemeTexture", 2D) = "white" {}
        _ThemeSize("ThemeSize", float) = 16

    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            float4 _Area;
            int _MaxIter;
            float _EscapeRadius;
            float _Speed;

            sampler2D _SpectrumTexture;
            int _SpectrumSize;

            sampler2D _ThemeTexture;
            int _ThemeSize;

            sampler2D _MainTex;

            fixed4 frag (v2f i) : SV_Target {
                // drawing stuff
                float2 uv = i.uv - 0.5;
                float2 offset = _Area.xy + uv * _Area.zw;

                // cool modulation
                float sub = tex2D(_SpectrumTexture, 0.0);
                float bass = tex2D(_SpectrumTexture, 0.25);
                float mids = tex2D(_SpectrumTexture, 0.50);
                float highs = tex2D(_SpectrumTexture, 0.75);

                float r = lerp(2.0, 200, bass);
                float maxIterations = lerp(2.0, 500, sub);

                // fractal bits
                float r2 = r*r;
                float2 c = _Area.xy + uv * _Area.zw;
                float2 z = 0;
                float2 zNext;
                int iter;
                for (iter = 0; iter < maxIterations; iter ++)
                {
                    // f(z) = z^2 + c
                    zNext.x = z.x * z.x - z.y * z.y   + c.x;
                    zNext.y = 2 * z.x * z.y           + c.y;
                    z = zNext;

                    // unbounded
                    if (length(zNext) > r)
                        break;
                }

                // in the set
                // make it white
                if (iter >= maxIterations) {
                    return 0;
                    return 1;
                }

                float val = iter / float(maxIterations);
                float4 col = tex2D(_ThemeTexture, float2(sub, 1.0));

                return col * val;

                // return float4(val, val, val, 1.0);
                // return tex2D(_ThemeTexture, highs);
                // float col = tex2D(_ThemeTexture, float2(highs * val, 1.0));
                // return col;

                // from spinny curvy brot
                // float dist  = length(z); // distance from origin
                // float fracIter  = (dist - r) / (r2 - r); // linear interpolation
                // fracIter = log2(log(dist) / log(r) ); // double exponential interpolation
                // iter -= fracIter;
                // float m = sqrt(iter / _MaxIter);
                // float4 col = sin(float4(.3, .45, .65, 1) * m * 20)*.5 + .5; // procedural colors
                // col = tex2D(_MainTex, float2(m * _Repeat + _Time.y*_Speed, _Color));
                // col *= smoothstep(3, 0, fracIter);
                // float angle = atan2(z.x, z.y);
                // col *= 1 + sin(angle*2 + _Time.y*4)*.2;
                // return col;
            }
            ENDCG
        }
    }
}