raytracing/in_one_weekend/src/camera.zig

const std = @import("std");
const math = std.math;

const Point3 = @import("vec3.zig").Point3;
const Vec3 = @import("vec3.zig").Vec3;
const Ray = @import("ray.zig").Ray;

fn degreesToRadians(degrees: f32) f32 {
    return degrees * math.pi / 180.0;
}

pub const Camera = struct {
    origin: Point3,
    lowerLeftCorner: Point3,
    horizontal: Vec3,
    vertical: Vec3,

    pub fn init(
        lookFrom: Point3,
        lookAt: Point3,
        vup: Vec3,
        vfov: f32,
        aspectRatio: f32,
    ) Camera {
        const theta = degreesToRadians(vfov);
        const h = math.tan(theta / 2);

        const viewportHeight = 2.0 * h;
        const viewportWidth = aspectRatio * viewportHeight;

        const w = lookFrom.sub(lookAt).unit();
        const u = vup.cross(w).unit();
        const v = w.cross(u);

        const origin = lookFrom;
        const horizontal = u.mul_s(viewportWidth);
        const vertical = v.mul_s(viewportHeight);
        const lowerLeftCorner = origin.sub(horizontal.div(2)).sub(vertical.div(2)).sub(w);

        return Camera {
            .origin = origin,
            .horizontal = horizontal,
            .vertical = vertical,
            .lowerLeftCorner = lowerLeftCorner,
        };
    }

    pub fn getRay(self: Camera, s: f32, t: f32) Ray {
        return Ray{
            .origin = self.origin,
            .direction = self.lowerLeftCorner.add(self.horizontal.mul_s(s)).add(self.vertical.mul_s(t)).sub(self.origin),
        };
    }
};