Refactor SDL2 interface code

src/engine/main.zig

@@ -6,16 +6,16 @@ const sys = @import("./sys.zig");
 /// Starts the the game engine.
 ///
 pub fn main() anyerror!void {
-    return nosuspend await async sys.runGraphics(anyerror, run);
+    return nosuspend await async sys.display(anyerror, run);
 }
 
-fn run(app: *sys.AppContext, graphics: *sys.GraphicsContext) anyerror!void {
+fn run(app: *sys.App, graphics: *sys.Graphics) anyerror!void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
 
     defer _ = gpa.deinit();
 
     {
-        var file_access = try app.data().open(try sys.Path.joined(&.{"ona.lua"}), .readonly);
+        var file_access = try app.data.open(try sys.Path.joined(&.{"ona.lua"}), .readonly);
 
         defer file_access.close();
 
@@ -27,7 +27,7 @@ fn run(app: *sys.AppContext, graphics: *sys.GraphicsContext) anyerror!void {
 
         if ((try file_access.read(buffer)) != file_size) return error.ScriptLoadFailure;
 
-        sys.Log.debug.write(buffer);
+        app.log(.debug, buffer);
     }
 
     while (graphics.poll()) |_| {

src/engine/sys.zig

@@ -1,5 +1,3 @@
-const Archive = @import("./sys/Archive.zig");
-
 const ext = @cImport({
     @cInclude("SDL2/SDL.h");
 });
@@ -9,222 +7,43 @@ const ona = @import("ona");
 const std = @import("std");
 
 ///
-/// A thread-safe platform abstraction over multiplexing system I/O processing and event handling.
+/// Thread-safe platform abstraction over multiplexing system I/O processing and event handling.
 ///
-pub const AppContext = opaque {
+pub const App = struct {
-    ///
+    message_chain: ?*Message = null,
-    /// Linked list of asynchronous messages chained together to be processed by the work processor.
-    ///
-    const Message = struct {
-        next: ?*Message = null,
-
-        kind: union(enum) {
-            quit,
-
-            task: struct {
-                data: *anyopaque,
-                action: fn (*anyopaque) void,
-                frame: anyframe,
-            },
-        },
-    };
-
-    ///
-    /// Internal state of the event loop hidden from the API consumer.
-    ///
-    const Implementation = struct {
-        user_path_prefix: [*]u8,
-        data_file_system: FileSystem,
-        user_file_system: FileSystem,
     message_semaphore: *ext.SDL_sem,
     message_mutex: *ext.SDL_mutex,
-        message_thread: ?*ext.SDL_Thread,
+    data: FileSystem,
-        messages: ?*Message = null,
+    user: FileSystem,
 
     ///
-        /// [StartError.OutOfSemaphores] indicates that the process has no more semaphores available
+    /// Enqueues `message` to the message chain in `app`.
-        /// to it for use, meaning an [Implementation] may not be initialized at this time.
     ///
-        /// [StartError.OutOfMutexes] indicates that the process has no more mutexes available to it
+    fn enqueue(app: *App, message: *Message) void {
-        /// for use, meaning an [Implementation] may not be initialized at this time.
-        ///
-        /// [StartError.OutOfMemory] indicates that the process has no more memory available to it
-        /// for use, meaning an [Implementation] may not be initialized at this time.
-        ///
-        const InitError = error {
-            OutOfSemaphores,
-            OutOfMutexes,
-            OutOfMemory,
-        };
-
-        ///
-        /// [StartError.OutOfThreads] indicates that the process has no more threads available to it
-        /// to use, meaning that no asynchronous work may be started on an [Implementation] at this
-        /// time.
-        ///
-        /// [StartError.AlreadyStarted] is occurs when a request to start work processing happens on
-        /// an [Implementation] that is already processing work.
-        ///
-        const StartError = error {
-            OutOfThreads,
-            AlreadyStarted,
-        };
-
-        ///
-        /// Casts `app_context` to a [Implementation] reference.
-        ///
-        /// *Note* that if `app_context` does not have the same alignment as [Implementation], safety-
-        /// checked undefined behavior will occur.
-        ///
-        fn cast(app_context: *AppContext) *Implementation {
-            return @ptrCast(*Implementation, @alignCast(@alignOf(Implementation), app_context));
-        }
-
-        ///
-        /// Deinitializes the `implementation`, requesting any running asynchronous workload
-        /// processes quit and waits for them to do so before freeing any resources.
-        ///
-        fn deinit(implementation: *Implementation) void {
-            var message = Message{.kind = .quit};
-
-            implementation.enqueue(&message);
-
-            {
-                var status = @as(c_int, 0);
-
-                // SDL2 defines waiting on a null thread reference as a no-op. See
-                // https://wiki.libsdl.org/SDL_WaitThread for more information
-                ext.SDL_WaitThread(implementation.message_thread, &status);
-
-                if (status != 0) {
-                    // TODO: Error check this.
-                }
-            }
-
-            implementation.data_file_system.archive.index_cache.deinit();
-            ext.SDL_free(implementation.user_path_prefix);
-            ext.SDL_DestroyMutex(implementation.message_mutex);
-            ext.SDL_DestroySemaphore(implementation.message_semaphore);
-        }
-
-        ///
-        /// Enqueues `message` to the message processor of `implementation` to be processed at a
-        /// later, non-deterministic point in time.
-        ///
-        fn enqueue(implementation: *Implementation, message: *Message) void {
         {
             // TODO: Error check these.
-                _ = ext.SDL_LockMutex(implementation.message_mutex);
+            _ = ext.SDL_LockMutex(app.message_mutex);
 
-                defer _ = ext.SDL_UnlockMutex(implementation.message_mutex);
+            defer _ = ext.SDL_UnlockMutex(app.message_mutex);
 
-                if (implementation.messages) |messages| {
+            if (app.message_chain) |message_chain| {
-                    messages.next = message;
+                message_chain.next = message;
             } else {
-                    implementation.messages = message;
+                app.message_chain = message;
             }
         }
 
         // TODO: Error check this.
-            _ = ext.SDL_SemPost(implementation.message_semaphore);
+        _ = ext.SDL_SemPost(app.message_semaphore);
     }
 
     ///
-        /// Initializes a new [Implemenation] with `data_archive_file_access` as the data archive to
+    /// Asynchronously executes `procedure` with `arguments` as an anonymous struct of its arguments
-        /// read from and `user_path_prefix` as the native writable user data directory.
+    /// and `app` as its execution context.
     ///
-        /// Returns the created [Implementation] value on success or [InitError] on failure.
+    /// Once the execution frame resumes, the value returned by executing `procedure` is returned.
     ///
-        fn init(allocator: std.mem.Allocator,
+    pub fn schedule(app: *App, procedure: anytype,
-            data_archive_file_access: ona.io.FileAccess) InitError!Implementation {
-
-            const user_path_prefix = ext.SDL_GetPrefPath("ona", "ona") orelse
-                return error.OutOfMemory;
-
-            return Implementation{
-                .user_file_system = .{.native =
-                    user_path_prefix[0 .. std.mem.len(user_path_prefix)]},
-
-                .message_semaphore = ext.SDL_CreateSemaphore(0) orelse return error.OutOfSemaphores,
-                .message_mutex = ext.SDL_CreateMutex() orelse return error.OutOfMutexes,
-                .user_path_prefix = user_path_prefix,
-
-                .data_file_system = .{.archive = .{
-                    .index_cache = try Archive.IndexCache.init(allocator),
-                    .file_access = data_archive_file_access,
-                }},
-
-                .message_thread = null,
-            };
-        }
-
-        ///
-        /// [FileSystemMessage] processing function used by a dedicated worker thread, where `data`
-        /// is a type-erased reference to a [EventLoop].
-        ///
-        /// The processor returns `0` if it exited normally or any other value if an erroneous exit
-        /// occured.
-        ///
-        fn processTasks(userdata: ?*anyopaque) callconv(.C) c_int {
-            const implementation = Implementation.cast(
-                @ptrCast(*AppContext, userdata orelse unreachable));
-
-            while (true) {
-                // TODO: Error check these.
-                _ = ext.SDL_SemWait(implementation.message_semaphore);
-                _ = ext.SDL_LockMutex(implementation.message_mutex);
-
-                defer _ = ext.SDL_UnlockMutex(implementation.message_mutex);
-
-                while (implementation.messages) |messages| {
-                    switch (messages.kind) {
-                        .quit => {
-                            return 0;
-                        },
-
-                        .task => |task| {
-                            task.action(task.data);
-
-                            resume task.frame;
-                        },
-                    }
-
-                    implementation.messages = messages.next;
-                }
-            }
-        }
-
-        ///
-        /// Attempts to start the asynchronous worker thread of `implementation` if it hasn't been
-        /// already.
-        ///
-        /// [StartError] is returned on failure.
-        ///
-        fn start(implementation: *Implementation) StartError!void {
-            if (implementation.message_thread != null) return error.AlreadyStarted;
-
-            implementation.message_thread = ext.SDL_CreateThread(processTasks,
-                "File System Worker", implementation) orelse {
-
-                ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION,
-                    "Failed to create file-system work processor");
-
-                return error.OutOfThreads;
-            };
-        }
-    };
-
-    ///
-    /// Returns a reference to the currently loaded data file-system.
-    ///
-    pub fn data(app_context: *AppContext) *FileSystem {
-        return &Implementation.cast(app_context).data_file_system;
-    }
-
-    ///
-    ///
-    ///
-    pub fn schedule(app_context: *AppContext, procedure: anytype,
         arguments: anytype) ona.meta.FnReturn(@TypeOf(procedure)) {
 
         const Task = struct {
@@ -246,7 +65,7 @@ pub const AppContext = opaque {
             .arguments = &arguments,
         };
 
-        var message = AppContext.Message{
+        var message = Message{
             .kind = .{.task = .{
                 .data = &task,
                 .action = Task.process,
@@ -254,14 +73,22 @@ pub const AppContext = opaque {
             }},
         };
 
-        suspend Implementation.cast(app_context).enqueue(&message);
+        suspend app.enqueue(&message);
     }
 
     ///
-    /// Returns a reference to the currently loaded user file-system.
+    /// Asynchronously logs `info` with `logger` as the logging method and `app` as the execution
+    /// context.
     ///
-    pub fn user(app_context: *AppContext) *FileSystem {
+    pub fn log(app: *App, logger: Logger, info: []const u8) void {
-        return &Implementation.cast(app_context).user_file_system;
+        var message = Message{
+            .kind = .{.log = .{
+                .logger = logger,
+                .info = info,
+            }},
+        };
+
+        app.enqueue(&message);
     }
 };
 
@@ -274,17 +101,48 @@ pub const FileSystem = union(enum) {
     archive: Archive,
 
     ///
-    /// With files typically being backed by a block device, they can produce a variety of
+    /// Archive file system information.
-    /// errors - from physical to virtual errors - these are all encapsulated by the API as
+    ///
-    /// general [OpenError.FileNotFound] errors.
+    const Archive = struct {
+        file_access: ona.io.FileAccess,
+        index_cache: IndexCache,
+        entry_table: [max_open_entries]Entry = std.mem.zeroes([max_open_entries]Entry),
+
+        ///
+        /// Hard limit on the maximum number of entries open at once.
+        ///
+        const max_open_entries = 16;
+
+        ///
+        /// Stateful extension of an [oar.Entry].
+        ///
+        const Entry = struct {
+            owner: ?*ona.io.FileAccess,
+            cursor: u64,
+            header: oar.Entry,
+        };
+
+        ///
+        /// Table cache for associating [oar.Path] values with offsets to entries in a given file.
+        ///
+        const IndexCache = ona.table.Hashed(oar.Path, u64, .{
+            .equals = oar.Path.equals,
+            .hash = oar.Path.hash,
+        });
+    };
+
+    ///
+    /// With files typically being backed by a block device, they can produce a variety of errors -
+    /// from physical to virtual errors - these are all encapsulated by the API as general
+    /// [OpenError.FileNotFound] errors.
     ///
     /// When a given [FileSystem] does not support a specified [OpenMode],
     /// [OpenError.ModeUnsupported] is used to inform the consuming code that another [OpenMode]
     /// should be tried or, if no mode other is suitable, that the resource is effectively
     /// unavailable.
     ///
-    /// If the number of known [FileAccess] handles has been exhausted, [OpenError.OutOfFiles]
+    /// If the number of known [FileAccess] handles has been exhausted, [OpenError.OutOfFiles] is
-    /// is used to communicate this.
+    /// used to communicate this.
     ///
     pub const OpenError = error {
         FileNotFound,
@@ -380,12 +238,13 @@ pub const FileSystem = union(enum) {
                         }
 
                         fn skip(context: *anyopaque, offset: i64) FileAccess.Error!void {
-                            const math = std.math;
                             const archive_entry = archiveEntryCast(context);
 
                             if (archive_entry.owner == null) return error.FileInaccessible;
 
                             if (offset < 0) {
+                                const math = std.math;
+
                                 archive_entry.cursor = math.max(0,
                                     archive_entry.cursor - math.absCast(offset));
                             } else {
@@ -447,17 +306,18 @@ pub const FileSystem = union(enum) {
             .native => |native| {
                 if (native.len == 0) return error.FileNotFound;
 
-                var path_buffer = std.mem.zeroes([4096]u8);
+                const mem = std.mem;
+                var path_buffer = mem.zeroes([4096]u8);
                 const seperator_length = @boolToInt(native[native.len - 1] != oar.Path.seperator);
 
                 if ((native.len + seperator_length + path.length) >=
                     path_buffer.len) return error.FileNotFound;
 
-                std.mem.copy(u8, path_buffer[0 ..], native);
+                mem.copy(u8, &path_buffer, native);
 
                 if (seperator_length != 0) path_buffer[native.len] = oar.Path.seperator;
 
-                std.mem.copy(u8, path_buffer[native.len .. path_buffer.
+                mem.copy(u8, path_buffer[native.len .. path_buffer.
                     len], path.buffer[0 .. path.length]);
 
                 const FileAccess = ona.io.FileAccess;
@@ -565,7 +425,7 @@ pub const FileSystem = union(enum) {
 ///
 ///
 ///
-pub const GraphicsContext = opaque {
+pub const Graphics = opaque {
     ///
     ///
     ///
@@ -587,8 +447,8 @@ pub const GraphicsContext = opaque {
     ///
     ///
     ///
-    pub fn poll(graphics_context: *GraphicsContext) ?*const Event {
+    pub fn poll(graphics: *Graphics) ?*const Event {
-        _ = graphics_context;
+        _ = graphics;
 
         return null;
     }
@@ -596,41 +456,46 @@ pub const GraphicsContext = opaque {
     ///
     ///
     ///
-    pub fn present(graphics_context: *GraphicsContext) void {
+    pub fn present(graphics: *Graphics) void {
         // TODO: Implement;
-        _ = graphics_context;
+        _ = graphics;
     }
 };
 
 ///
-/// Returns a graphics runner that uses `Errors` as its error set.
+/// [Logger.info] logs information that isn't necessarily an error but indicates something useful to
+/// be logged.
 ///
-pub fn GraphicsRunner(comptime Errors: type) type {
+/// [Logger.debug] logs information only when the engine is in debug mode.
-    return fn (*AppContext, *GraphicsContext) callconv(.Async) Errors!void;
-}
-
 ///
-/// [Log.info] represents a log message which is purely informative and does not indicate any kind
+/// [Logger.warning] logs information to indicate a non-critical error has occured.
-/// of issue.
 ///
-/// [Log.debug] represents a log message which is purely for debugging purposes and will only occurs
+pub const Logger = enum(u32) {
-/// in debug builds.
-///
-/// [Log.warning] represents a log message which is a warning about a issue that does not break
-/// anything important but is not ideal.
-///
-pub const Log = enum(u32) {
     info = ext.SDL_LOG_PRIORITY_INFO,
     debug = ext.SDL_LOG_PRIORITY_DEBUG,
     warning = ext.SDL_LOG_PRIORITY_WARN,
+};
 
 ///
-    /// Writes `utf8_message` as the log kind identified by `log`.
+/// Linked list of asynchronous messages chained together to be processed by the work processor.
 ///
-    pub fn write(log: Log, utf8_message: []const u8) void {
+pub const Message = struct {
-        ext.SDL_LogMessage(ext.SDL_LOG_CATEGORY_APPLICATION,
+    next: ?*Message = null,
-            @enumToInt(log), "%.*s", utf8_message.len, utf8_message.ptr);
+
-    }
+    kind: union(enum) {
+        quit,
+
+        log: struct {
+            logger: Logger,
+            info: []const u8,
+        },
+
+        task: struct {
+            data: *anyopaque,
+            action: fn (*anyopaque) void,
+            frame: anyframe,
+        },
+    },
 };
 
 ///
@@ -639,13 +504,10 @@ pub const Log = enum(u32) {
 pub const Path = oar.Path;
 
 ///
-/// [RunError.InitFailure] occurs if a necessary resource fails to be acquired or allocated.
+/// [RunError.InitFailure] occurs when the runtime fails to initialize.
-///
-/// [RunError.AlreadyRunning] occurs if a runner has already been started.
 ///
 pub const RunError = error {
     InitFailure,
-    AlreadyRunning,
 };
 
 ///
@@ -654,8 +516,76 @@ pub const RunError = error {
 /// Should an error from `run` occur, an `Error` is returned, otherwise a [RunError] is returned if
 /// the underlying runtime fails and is logged.
 ///
-pub fn runGraphics(comptime Error: anytype,
+pub fn display(comptime Error: anytype,
-    comptime run: GraphicsRunner(Error)) (RunError || Error)!void {
+    comptime run: fn (*App, *Graphics) callconv(.Async) Error!void) (RunError || Error)!void {
+
+    var cwd = FileSystem{.native = "./"};
+    const user_prefix = ext.SDL_GetPrefPath("ona", "ona") orelse return error.InitFailure;
+
+    defer ext.SDL_free(user_prefix);
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+
+    defer if (gpa.deinit())
+        ext.SDL_LogWarn(ext.SDL_LOG_CATEGORY_APPLICATION, "Runtime allocator leaked memory");
+
+    var app = App{
+        .user = .{.native = std.mem.sliceTo(user_prefix, 0)},
+
+        .message_semaphore = ext.SDL_CreateSemaphore(0) orelse {
+            ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, "Failed to create message semaphore");
+
+            return error.InitFailure;
+        },
+
+        .message_mutex = ext.SDL_CreateMutex() orelse {
+            ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, "Failed to create message mutex");
+
+            return error.InitFailure;
+        },
+
+        .data = .{.archive = .{
+            .index_cache = FileSystem.Archive.IndexCache.init(gpa.allocator()) catch
+                return error.InitFailure,
+
+            .file_access = cwd.open(try Path.joined(&.{"./data.oar"}), .readonly) catch {
+                ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, "Failed to load ./data.oar");
+
+                return error.InitFailure;
+            },
+        }},
+    };
+
+    defer {
+        app.data.archive.file_access.close();
+        app.data.archive.index_cache.deinit();
+        ext.SDL_DestroySemaphore(app.message_semaphore);
+        ext.SDL_DestroyMutex(app.message_mutex);
+    }
+
+    const message_thread = ext.SDL_CreateThread(processMessages, "Message Processor", &app) orelse {
+        ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, "Failed to create message processor");
+
+        return error.InitFailure;
+    };
+
+    defer {
+        var message = Message{.kind = .quit};
+
+        app.enqueue(&message);
+
+        {
+            var status = std.mem.zeroes(c_int);
+
+            // SDL2 defines waiting on a null thread reference as a no-op. See
+            // https://wiki.libsdl.org/SDL_WaitThread for more information
+            ext.SDL_WaitThread(message_thread, &status);
+
+            if (status != 0) {
+                // TODO: Error check this.
+            }
+        }
+    }
 
     if (ext.SDL_Init(ext.SDL_INIT_EVERYTHING) != 0) {
         ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, "Failed to initialize runtime");
@@ -690,42 +620,47 @@ pub fn runGraphics(comptime Error: anytype,
 
     defer ext.SDL_DestroyRenderer(renderer);
 
-    var cwd_file_system = FileSystem{.native ="./"};
+    var graphics = Graphics.Implementation{
-    var data_access = try cwd_file_system.open(try Path.joined(&.{"./data.oar"}), .readonly);
-
-    defer data_access.close();
-
-    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
-
-    defer _ = gpa.deinit();
-
-    var app_context = AppContext.Implementation.init(gpa.allocator(), data_access) catch |err| {
-        ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, switch (err) {
-            error.OutOfMemory => "Failed to allocate necessary memory",
-            error.OutOfMutexes => "Failed to create file-system work lock",
-            error.OutOfSemaphores => "Failed to create file-system work scheduler",
-        });
-
-        return error.InitFailure;
-    };
-
-    defer app_context.deinit();
-
-    app_context.start() catch |err| {
-        ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, switch (err) {
-            // Not possible for it to have already been started.
-            error.AlreadyStarted => unreachable,
-            error.OutOfThreads => "Failed to start file-system work processor",
-        });
-
-        return error.InitFailure;
-    };
-
-    var graphics_context = GraphicsContext.Implementation{
         .event = .{
 
         },
     };
 
-    return run(@ptrCast(*AppContext, &app_context), @ptrCast(*GraphicsContext, &graphics_context));
+    return run(@ptrCast(*App, &app), @ptrCast(*Graphics, &graphics));
+}
+
+///
+/// [FileSystemMessage] processing function used by a dedicated worker thread, where `data`
+/// is a type-erased reference to a [EventLoop].
+///
+/// The processor returns `0` if it exited normally or any other value if an erroneous exit
+/// occured.
+///
+pub fn processMessages(userdata: ?*anyopaque) callconv(.C) c_int {
+    const app = @ptrCast(*App, @alignCast(@alignOf(App), userdata orelse unreachable));
+
+    while (true) {
+        // TODO: Error check these.
+        _ = ext.SDL_SemWait(app.message_semaphore);
+        _ = ext.SDL_LockMutex(app.message_mutex);
+
+        defer _ = ext.SDL_UnlockMutex(app.message_mutex);
+
+        while (app.message_chain) |message| {
+            switch (message.kind) {
+                .quit => return 0,
+
+                .log => |log| ext.SDL_LogMessage(ext.SDL_LOG_CATEGORY_APPLICATION,
+                    @enumToInt(log.logger), "%.*s", log.info.len, log.info.ptr),
+
+                .task => |task| {
+                    task.action(task.data);
+
+                    resume task.frame;
+                },
+            }
+
+            app.message_chain = message.next;
+        }
+    }
 }

src/engine/sys/Archive.zig

@@ -1,29 +0,0 @@
-const oar = @import("oar");
-const ona = @import("ona");
-const std = @import("std");
-
-file_access: ona.io.FileAccess,
-index_cache: IndexCache,
-entry_table: [max_open_entries]Entry = std.mem.zeroes([max_open_entries]Entry),
-
-///
-/// Hard limit on the maximum number of entries open at once.
-///
-const max_open_entries = 16;
-
-///
-/// Stateful extension of an [oar.Entry].
-///
-pub const Entry = struct {
-    owner: ?*ona.io.FileAccess,
-    cursor: u64,
-    header: oar.Entry,
-};
-
-///
-/// Table cache for associating [oar.Path] values with offsets to entries in a given file.
-///
-pub const IndexCache = ona.table.Hashed(oar.Path, u64, .{
-    .equals = oar.Path.equals,
-    .hash = oar.Path.hash,
-});

src/oar/main.zig

@@ -30,7 +30,7 @@ pub const Entry = extern struct {
         const origin = try file_access.queryCursor();
 
         if (((try file_access.read(std.mem.asBytes(&entry))) != @sizeOf(Entry)) and
-            ona.io.equalsBytes(entry.signature[0 ..], signature_magic[0 ..])) {
+            ona.io.equalsBytes(&entry.signature, &signature_magic)) {
 
             try file_access.seek(origin);