1 files changed, 29 insertions, 7 deletions

diff --git a/src/main.zig b/src/main.zig
index 2d42772..7ae5c9e 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,6 +1,16 @@
 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 {
+    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);
@@ -9,14 +19,28 @@ pub fn write_color(stdout: anytype, v: vec) !void {
 }
 
 const vec = @Vector(3, f32);
+pub fn scalar(x: f32) vec {
+    return @splat(3, x);
+}
+
+const ray = struct { origin: vec, direction: vec };
 
 pub fn main() !void {
-    const width = 512;
-    const height = 512;
+    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;
@@ -24,11 +48,9 @@ pub fn main() !void {
         warn("remaining: {}\n", .{j});
         var i: usize = 0;
         while (i < width) : (i += 1) {
-            var color = vec{
-                @intToFloat(f32, i) / (width - 1),
-                @intToFloat(f32, j) / (height - 1),
-                0.25,
-            };
+            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);
         }