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
        _Color("Color", range(0,1)) = 0.5
        _Repeat("Repeat", float) =  1
        _Speed("Speed", range(0, 1)) = 0.1
        _Colors("Colors", vector) = (3.0, 4.0, 5.0, 0.0)
    }
    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;
            float _Angle;
            float _Color;
            float3  _Colors;
            float _Repeat;
            float _Speed;
            int _MaxIter;
            sampler2D _MainTex;

            float2 rot(float2 p, float2 pivot, float a) {
                float s = sin(a);
                float c = cos(a);
                p -= pivot;
                p = float2(p.x*c-p.y*s, p.x*s+p.y*c);
                p += pivot;

                return p;
            }

            fixed4 frag (v2f i) : SV_Target {
                float2 uv = i.uv - 0.5;
                float2 offset = _Area.xy + uv * _Area.zw;
                float2 z;  // track pixel jumping across screen
                float2 zPrev;
                float r = 20;  // escape radius
                float r2 = r*r;

                float vxsquare = 0;
                float vysquare = 0;

                float iteration = 0;
                float lastIteration = _MaxIter;

                do {
                    vxsquare = uv.x * uv.x;
                    vysquare = uv.y * uv.y;

                    uv = float2(vxsquare - vysquare, uv.x * uv.y * 2) + offset;

                    iteration++;

                    if ((lastIteration == _MaxIter) && (vxsquare + vysquare) > 4.0) {
                        lastIteration = iteration + 1;
                    }
                } while (iteration < lastIteration);

                float val = (float(iteration) - (log(log(sqrt(vxsquare + vysquare))) / log(2.0))) / float(_MaxIter);
                return float4(sin(val * _Colors.x), sin(val * _Colors.y), sin(val * _Colors.z), 1);

                // 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
        }
    }
}