background.h

#pragma once
#include "vector.h"
#include <cmath>

class Background {
public:
    virtual Vector3 sample(Vector3 direction) const = 0;
};

class SolidColorBackground: public Background {
public:
    Vector3 color;
    double intensity;

    SolidColorBackground(Vector3 color = Vector3(1, 1, 1), double intensity = 1): color(color), intensity(intensity) {};
    Vector3 sample(Vector3 direction) const override {
        return color * intensity;
    };
};

class PanoramaBackground: public Background {
public:
    Vector3** texture = nullptr;
    Vector3 texture_dim = Vector3();
    double intensity;

    PanoramaBackground(Vector3** texture, Vector3 texture_dim, double intensity = 1): texture(texture), texture_dim(texture_dim), intensity(intensity) {}
    Vector3 sample(Vector3 direction) const override {
        double theta = atan2(direction.z, direction.x);
        double phi = acos(direction.y);
        double u = (theta + M_PI) / (2 * M_PI);
        double v = phi / M_PI;
        int x = u * texture_dim.x;
        int y = v * texture_dim.y;

        return texture[y][x];
    }
};