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const std = @import("std");
const warn = @import("std").debug.print;
pub fn unit_vector(v: vec) vec {
return v / scalar(3);
}
pub fn ray_color(r: ray) vec {
if (hit_sphere(vec{ 0, 0, -1 }, 0.5, r)) {
return vec{ 1.0, 0, 0 };
}
const direction = unit_vector(r.direction);
const t = 0.5 * (direction[1] + 1.0);
return scalar(1.0 - t) * vec{ 1.0, 1.0, 1.0 } + scalar(t) * vec{ 0.5, 0.7, 1.0 };
}
pub fn write_color(stdout: anytype, v: vec) !void {
const r = @floatToInt(usize, v[0] * 255.999);
const g = @floatToInt(usize, v[1] * 255.999);
const b = @floatToInt(usize, v[2] * 255.999);
try stdout.print("{} {} {}\n", .{ r, g, b });
}
pub fn hit_sphere(center: vec, radius: f32, r: ray) bool {
const oc = r.origin - center;
const a = dot(r.direction, r.direction);
const b = 2 * dot(oc, r.direction);
const c = dot(oc, oc) - radius * radius;
const discriminant = b * b - 4 * a * c;
return discriminant > 0;
}
const vec = @Vector(3, f32);
pub fn scalar(x: f32) vec {
return @splat(3, x);
}
pub fn dot(x: vec, y: vec) f32 {
return x[0] * y[0] + x[1] * y[1] + x[2] * y[2];
}
const ray = struct { origin: vec, direction: vec };
pub fn main() !void {
const aspect_ratio: f32 = 16.0 / 9.0;
const width: usize = 1000;
const height: usize = @floatToInt(usize, @intToFloat(f32, width) / aspect_ratio);
const stdout_file = std.io.getStdOut().writer();
var bw = std.io.bufferedWriter(stdout_file);
const stdout = bw.writer();
const viewport_height = 2.0;
const viewport_width = aspect_ratio * viewport_height;
const focal_length = 1.0;
const origin = vec{ 0, 0, 0 };
const horizontal = vec{ viewport_width, 0, 0 };
const vertical = vec{ 0, viewport_height, 0 };
const lower_left_corner = origin - (horizontal / scalar(2.0)) - (vertical / scalar(2.0)) - vec{ 0, 0, focal_length };
try stdout.print("P3\n{} {}\n255\n", .{ width, height });
var j: usize = height;
while (j > 0) : (j -= 1) {
warn("remaining: {}\n", .{j});
var i: usize = 0;
while (i < width) : (i += 1) {
var u = scalar(@intToFloat(f32, i) / @intToFloat(f32, width - 1));
var v = scalar(@intToFloat(f32, j) / @intToFloat(f32, height - 1));
var color = ray_color(ray{ .origin = origin, .direction = lower_left_corner + u * horizontal + v * vertical - origin });
try write_color(stdout, color);
}
}
try bw.flush();
}
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