Add Lua as dependency via SHA-pinned submodule

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "ext/lua"]
+	path = ext/lua
+	url = git@github.com:lua/lua.git

build.zig

@@ -11,8 +11,55 @@ pub fn build(builder: *std.build.Builder) void {
         ona_exe.setTarget(target);
         ona_exe.setBuildMode(mode);
         ona_exe.install();
+        ona_exe.addIncludeDir("./ext");
         ona_exe.linkSystemLibrary("sdl2");
 
+        // Lua dependency.
+        ona_exe.linkLibrary(link_lua: {
+            const lua_lib = builder.addStaticLibrary("lua", null);
+
+            lua_lib.addIncludeDir("./ext/lua");
+            lua_lib.linkLibC();
+
+            // TODO: Implement support for more than Linux.
+            lua_lib.addCSourceFiles(&.{
+                "./ext/lua/lapi.c",
+                "./ext/lua/lauxlib.c",
+                "./ext/lua/lbaselib.c",
+                "./ext/lua/lcode.c",
+                "./ext/lua/lcorolib.c",
+                "./ext/lua/lctype.c",
+                "./ext/lua/ldblib.c",
+                "./ext/lua/ldebug.c",
+                "./ext/lua/ldo.c",
+                "./ext/lua/ldump.c",
+                "./ext/lua/lfunc.c",
+                "./ext/lua/lgc.c",
+                "./ext/lua/llex.c",
+                "./ext/lua/lmathlib.c",
+                "./ext/lua/lmem.c",
+                "./ext/lua/loadlib.c",
+                "./ext/lua/lobject.c",
+                "./ext/lua/lopcodes.c",
+                "./ext/lua/loslib.c",
+                "./ext/lua/lparser.c",
+                "./ext/lua/lstate.c",
+                "./ext/lua/lstring.c",
+                "./ext/lua/lstrlib.c",
+                "./ext/lua/ltablib.c",
+                "./ext/lua/lundump.c",
+                "./ext/lua/lutf8lib.c",
+                "./ext/lua/lvm.c",
+                "./ext/lua/lzio.c",
+                "./ext/lua/ltable.c",
+                "./ext/lua/ltm.c",
+            }, &.{"-DLUA_USE_LINUX", "-Wl"});
+
+            lua_lib.install();
+
+            break: link_lua lua_lib;
+        });
+
         const run_cmd = ona_exe.run();
 
         run_cmd.step.dependOn(builder.getInstallStep());

ext/lua

@@ -0,0 +1 @@
+Subproject commit 5d708c3f9cae12820e415d4f89c9eacbe2ab964b

ona.lua

@@ -0,0 +1,8 @@
+
+return {
+    name = "Ona",
+    initial_width = 1280,
+    initial_height = 800,
+
+    initial_scene = nil,
+}

src/main.zig

@@ -1,18 +1,64 @@
 const c = @cImport({
     @cInclude("SDL2/SDL.h");
+    @cInclude("lua/lua.h");
+    @cInclude("lua/lualib.h");
+    @cInclude("lua/lauxlib.h");
 });
 
 const std = @import("std");
 
+fn luaAlloc(userdata: ?*anyopaque, ptr: ?*anyopaque, original_size: usize,
+    updated_size: usize) callconv(.C) ?*anyopaque {
+
+    // Implementation derived from
+    // https://github.com/natecraddock/ziglua/blob/master/src/ziglua.zig.
+    const alignment = @alignOf(std.c.max_align_t);
+    const Allocator = std.mem.Allocator;
+    const allocator = @ptrCast(*Allocator, @alignCast(@alignOf(Allocator), userdata.?));
+
+    if (@ptrCast(?[*]align(alignment) u8, @alignCast(alignment, ptr))) |prev_ptr| {
+        // Allocator is working with an existing pointer.
+        const prev_slice = prev_ptr[0 .. original_size];
+
+        if (updated_size == 0) {
+            // Updated size of `0` to free the existing memory block.
+            allocator.free(prev_slice);
+
+            return null;
+        }
+
+        // Resize the existing memory block.
+        return (allocator.reallocAdvanced(prev_slice, alignment,
+            updated_size, .exact) catch return null).ptr;
+    }
+
+    // No existing pointer, allocate a new block of memory.
+    return (allocator.alignedAlloc(u8, alignment, updated_size) catch return null).ptr;
+}
+
 pub fn main() anyerror!void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+
     if (c.SDL_Init(c.SDL_INIT_EVERYTHING) != 0) {
-        c.SDL_LogCritical(c.SDL_LOG_CATEGORY_APPLICATION, "Failed to initialize SDL2");
+        c.SDL_LogCritical(c.SDL_LOG_CATEGORY_APPLICATION, "Failed to initialize SDL2 runtime");
 
         return error.SystemFailure;
     }
 
     defer c.SDL_Quit();
 
+    var lua_allocator = gpa.allocator();
+    const lua_state = c.lua_newstate(luaAlloc, @ptrCast(*anyopaque, &lua_allocator));
+
+    if (lua_state == null) {
+        c.SDL_LogCritical(c.SDL_LOG_CATEGORY_APPLICATION,
+            "Failed to initialize Lua virtual machine");
+
+        return error.SystemFailure;
+    }
+
+    defer c.lua_close(lua_state);
+
     const sdl_window = create_sdl_window: {
         const pos = c.SDL_WINDOWPOS_UNDEFINED;
         var flags = @as(u32, 0);
@@ -21,13 +67,27 @@ pub fn main() anyerror!void {
     };
 
     if (sdl_window == null) {
-        c.SDL_LogCritical(c.SDL_LOG_CATEGORY_APPLICATION, "Failed to create window");
+        c.SDL_LogCritical(c.SDL_LOG_CATEGORY_VIDEO, "Failed to create SDL2 window");
 
         return error.SystemFailure;
     }
 
     defer c.SDL_DestroyWindow(sdl_window);
 
+    const sdl_renderer = create_sdl_renderer: {
+        var flags = @as(u32, 0);
+
+        break: create_sdl_renderer c.SDL_CreateRenderer(sdl_window, -1, flags);
+    };
+
+    if (sdl_renderer == null) {
+        c.SDL_LogCritical(c.SDL_LOG_CATEGORY_VIDEO, "Failed to create SDL2 renderer");
+
+        return error.SystemFailure;
+    }
+
+    defer c.SDL_DestroyRenderer(sdl_renderer);
+
     var is_running = true;
 
     while (is_running) {
@@ -40,5 +100,10 @@ pub fn main() anyerror!void {
                 else => {},
             }
         }
+
+        _ = c.SDL_SetRenderDrawColor(sdl_renderer, 0, 0, 0, 255);
+        _ = c.SDL_RenderClear(sdl_renderer);
+
+        c.SDL_RenderPresent(sdl_renderer);
     }
 }