mach: Added runtime application options

Reused mach.Options for run time options. It is set with
Engine.setOptions function. ``pub const options`` on top level App has
no effect and will be ignored completely.

Added a blank struct StartupOptions which would be used for startup time
options in future. Currently they aren't used for anything.

src/Engine.zig

@@ -34,10 +34,10 @@ target_desc: gpu.SwapChain.Descriptor,
 
 internal: platform.Type,
 
-pub fn init(allocator: std.mem.Allocator, options: structs.Options) !Engine {
+pub fn init(allocator: std.mem.Allocator) !Engine {
     var engine: Engine = undefined;
     engine.allocator = allocator;
-    engine.options = options;
+    engine.options = structs.Options{};
     engine.timer = try Timer.start();
 
     engine.internal = try platform.Type.init(allocator, &engine);
@@ -45,6 +45,14 @@ pub fn init(allocator: std.mem.Allocator, options: structs.Options) !Engine {
     return engine;
 }
 
+/// Set runtime options for application, like title, window size etc.
+///
+/// See mach.Options for details
+pub fn setOptions(engine: *Engine, options: structs.Options) !void {
+    try engine.internal.setOptions(options);
+    engine.options = options;
+}
+
 pub fn setShouldClose(engine: *Engine, value: bool) void {
     engine.internal.setShouldClose(value);
 }

src/platform/native.zig

@@ -235,6 +235,11 @@ pub const Platform = struct {
         platform.window.setFramebufferSizeCallback(framebuffer_size_callback);
     }
 
+    pub fn setOptions(platform: *Platform, options: structs.Options) !void {
+        try platform.window.setSize(.{ .width = options.width, .height = options.height });
+        try platform.window.setTitle(options.title);
+    }
+
     pub fn setShouldClose(platform: *Platform, value: bool) void {
         platform.window.setShouldClose(value);
     }
@@ -410,8 +415,7 @@ pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
     const allocator = gpa.allocator();
 
-    const options = if (@hasDecl(App, "options")) App.options else structs.Options{};
+    var engine = try Engine.init(allocator);
-    var engine = try Engine.init(allocator, options);
     var app: App = undefined;
 
     try app.init(&engine);

src/platform/wasm.zig

@@ -42,6 +42,13 @@ pub const Platform = struct {
         };
     }
 
+    pub fn setOptions(platform: *Platform, options: structs.Options) !void {
+        js.machCanvasSetSize(platform.id, options.width, options.height);
+
+        const title = std.mem.span(options.title);
+        js.machCanvasSetTitle(platform.id, title.ptr, title.len);
+    }
+
     pub fn setShouldClose(_: *Platform, _: bool) void {}
 
     pub fn getFramebufferSize(platform: *Platform) structs.Size {
@@ -116,11 +123,7 @@ export fn wasmInit() void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
     const allocator = gpa.allocator();
 
-    // NOTE: On wasm, vsync is double by default and cannot be changed.
+    engine = Engine.init(allocator) catch unreachable;
-    // Hence options.vsync is not used anywhere.
-    const options = if (@hasDecl(App, "options")) App.options else structs.Options{};
-    engine = Engine.init(allocator, options) catch unreachable;
-
     app.init(&engine) catch {};
 }
 

src/structs.zig

@@ -12,6 +12,9 @@ pub const SizeOptional = struct {
 };
 
 /// Application options that can be configured at init time.
+pub const StartupOptions = struct {};
+
+/// Application options that can be configured at run time.
 pub const Options = struct {
     /// The title of the window.
     title: [*:0]const u8 = "Mach engine",