feat: generate image

.gitignore

@@ -1,2 +1,3 @@
 .zig-cache
 zig-out
+*.ppm

src/main.zig

@@ -1,13 +1,29 @@
 const std = @import("std");
 
 pub fn main() !void {
-    var allocator = std.heap.ArenaAllocator{};
-    defer allocator.deinit();
+    const img_width = 512;
+    const img_height = 512;
 
-    const alloc = allocator.allocator();
+    var buf: [img_width * img_height * 3]u8 = undefined;
 
-    const hello_world = try std.fmt.allocPrint(alloc, "Hello, World!\n", .{});
-    defer allocator.free(hello_world);
+    const stdout = std.fs.File.stdout();
+    var writer_f: std.fs.File.Writer = stdout.writer(&buf);
+    var writer = &writer_f.interface;
 
-    std.debug.print("All your {s} are belong to us.\n", .{"codebase"});
+    try writer.print("P3\n{d} {d}\n255\n", .{ img_width, img_height });
+    try writer.flush();
+    for (0..img_height) |j| {
+        for (0..img_width) |i| {
+            const r = @as(f64, @floatFromInt(j)) / (img_width - 1);
+            const g = 0.0;
+            const b = @as(f64, @floatFromInt(i)) / (img_height - 1);
+
+            const ir = @as(i64, @intFromFloat(r * 255.999));
+            const ig = @as(i64, @intFromFloat(g * 255.999));
+            const ib = @as(i64, @intFromFloat(b * 255.999));
+
+            try writer.print("{d} {d} {d}\n", .{ ir, ig, ib });
+        }
+    }
+    try writer.flush();
 }