#include "rt_weekend.h"
#include "ray.h"

bool hit_sphere(const vec3 &center, float radius, const ray &r)
{
    vec3 oc = r.origin() - center;
    float a = dot(r.direction(), r.direction());
    float b = 2.0 * dot(oc, r.direction());
    float c = dot(oc, oc) - radius * radius;
    float discriminant = b * b - 4 * a * c;

    return (discriminant > 0);
}

vec3 color (const ray &r)
{
    if (hit_sphere(vec3(0, 0, -1), 0.5, r))
        return vec3(1, 0, 0);
    vec3 unit_direction = unit_vector(r.direction());
    float t = 0.5 * (unit_direction.y() + 1.0);
    return (1.0 - t) * vec3(1.0, 1.0, 1.0) + t * vec3(0.5, 0.7, 1.0);
}

extern "C"
void
PluginUpdateAndRender(plugin_offscreen_buffer *Buffer)
{
    int Pitch = Buffer->Pitch;
    uint8_t *Row = (uint8_t *)Buffer->Memory;

    vec3 lower_left_corner(-2.0, -1.0, -1.0);
    vec3 horizontal(4.0, 0.0, 0.0);
    vec3 vertical(0.0, 2.0, 0.0);
    vec3 origin(0.0, 0.0, 0.0);


    for(int j = Buffer->Height - 1; j >= 0; j--)
    {
        uint32_t *Pixel = (uint32_t *)Row;
        for(int i = 0; i < Buffer->Width; i++)
        {
            float u = float(i) / float(Buffer->Width);
            float v = float(j) / float(Buffer->Height);
            ray r(origin, lower_left_corner + u * horizontal + v * vertical);
            vec3 col = color(r);
            int ir = int(255.99 * col[0]);
            int ig = int(255.99 * col[1]);
            int ib = int(255.99 * col[2]);

            *Pixel++ = (ir << 24) + (ig << 16) + (ib << 8) + 0xFF;
        }

        Row += Pitch;
    }
}