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const std = @import("std");
const debug = std.debug;
const Vec3 = struct {
x: f64,
y: f64,
z: f64,
pub fn norm(v: Vec3) f64 {
return @sqrt(v.normSquared());
}
pub fn normSquared(v: Vec3) f64 {
return v.x * v.x + v.y * v.y + v.z * v.z;
}
pub fn dot(u: Vec3, v: Vec3) f64 {
return u.x * v.x + u.y * v.y + u.z * v.z;
}
pub fn cross(u: Vec3, v: Vec3) Vec3 {
return Vec3{
.x = u.y * v.z - u.z * v.y,
.y = u.z * v.x - u.x * v.z,
.z = u.x * v.y - u.y * v.x,
};
}
pub fn normalized(v: Vec3) Vec3 {
const n = v.norm();
if (n == 0.0) {
return v;
} else {
return v.div(n);
}
}
pub fn add(u: Vec3, v: Vec3) Vec3 {
return Vec3{
.x = u.x + v.x,
.y = u.y + v.y,
.z = u.z + v.z,
};
}
pub fn sub(u: Vec3, v: Vec3) Vec3 {
return Vec3{
.x = u.x - v.x,
.y = u.y - v.y,
.z = u.z - v.z,
};
}
pub fn mul(v: Vec3, t: f64) Vec3 {
return Vec3{
.x = v.x * t,
.y = v.y * t,
.z = v.z * t,
};
}
pub fn div(v: Vec3, t: f64) Vec3 {
return Vec3{
.x = v.x / t,
.y = v.y / t,
.z = v.z / t,
};
}
pub fn pp(v: Vec3) void {
debug.print("{} {} {}\n", .{ v.x, v.y, v.z });
}
};
const Point3 = Vec3;
const Color = Vec3;
const Ray = struct {
origin: Vec3,
dir: Vec3,
pub fn at(r: Ray, t: f64) Point3 {
return r.origin.add(r.dir.mul(t));
}
};
fn hitSphere(center: Point3, radius: f64, r: Ray) bool {
const oc = r.origin.sub(center);
const a = Vec3.dot(r.dir, r.dir);
const b = 2.0 * Vec3.dot(oc, r.dir);
const c = Vec3.dot(oc, oc) - radius * radius;
const discriminant = b * b - 4.0 * a * c;
return discriminant > 0.0;
}
fn rayColor(r: Ray) Color {
if (hitSphere(Point3{ .x = 0.0, .y = 0.0, .z = -1.0 }, 0.5, r)) {
return Color{ .x = 1.0, .y = 0.0, .z = 0.0 };
}
const unit_dir = r.dir.normalized();
const t = 0.5 * (unit_dir.y + 1.0);
return (Color{ .x = 1.0, .y = 1.0, .z = 1.0 }).mul(1.0 - t).add((Color{ .x = 0.5, .y = 0.7, .z = 1.0 }).mul(t));
}
fn writeColor(out: anytype, c: Color) !void {
try out.print("{} {} {}\n", .{
@floatToInt(u8, 255.999 * c.x),
@floatToInt(u8, 255.999 * c.y),
@floatToInt(u8, 255.999 * c.z),
});
}
pub fn main() !void {
// Image
const aspect_ratio = 16.0 / 9.0;
const image_width = 400;
const image_height = @floatToInt(comptime_int, @divTrunc(image_width, aspect_ratio));
// Camera
const viewport_height = 2.0;
const viewport_width = aspect_ratio * viewport_height;
const focal_length = 1.0;
const origin = Point3{ .x = 0.0, .y = 0.0, .z = 0.0 };
const horizontal = Vec3{ .x = viewport_width, .y = 0.0, .z = 0.0 };
const vertial = Vec3{ .x = 0.0, .y = viewport_height, .z = 0.0 };
const lower_left_corner = origin.sub(horizontal.div(2.0)).sub(vertial.div(2.0)).sub(Vec3{ .x = 0.0, .y = 0.0, .z = focal_length });
// Render
const stdout_file = std.io.getStdOut().writer();
var bw = std.io.bufferedWriter(stdout_file);
const stdout = bw.writer();
try stdout.print("P3\n{} {}\n255\n", .{ image_width, image_height });
var j: i32 = image_height - 1;
while (j >= 0) : (j -= 1) {
std.debug.print("\rScanlines remaining: {}", .{j});
var i: i32 = 0;
while (i < image_width) : (i += 1) {
const u = @intToFloat(f64, i) / (image_width - 1);
const v = @intToFloat(f64, j) / (image_height - 1);
const dir = lower_left_corner.add(horizontal.mul(u)).add(vertial.mul(v)).sub(origin);
const r = Ray{ .origin = origin, .dir = dir };
const pixelColor = rayColor(r);
try writeColor(stdout, pixelColor);
}
}
try bw.flush();
}
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