cbuffer ViewportBuffer : register(b0)
{
    float xmin;
    float xmax;
    float ymin;
    float ymax;
    int max_iter;
};

struct PS_IN { float4 pos : SV_POSITION; };

float4 PSMain(PS_IN input) : SV_TARGET
{
    float2 uv = input.pos.xy * 0.5 + 0.5; // [-1,1] -> [0,1]
    float2 c = float2(xmin,ymin) + uv * float2(xmax-xmin, ymax-ymin);
    float2 z = c;
    int i;
    for(i=0;i<max_iter;i++){
        if(dot(z,z)>4) break;
        z = float2(z.x*z.x - z.y*z.y, 2*z.x*z.y)+c;
    }
    float t = i/(float)max_iter;
    return float4(t,0.5*t,1.0-t,1);
}