mach: implement App struct in terms of unified entry point

src/Engine.zig

@@ -0,0 +1,81 @@
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+const glfw = @import("glfw");
+const gpu = @import("gpu");
+
+pub const VSyncMode = enum {
+    /// Potential screen tearing.
+    /// No synchronization with monitor, render frames as fast as possible.
+    none,
+
+    /// No tearing, synchronizes rendering with monitor refresh rate, rendering frames when ready.
+    ///
+    /// Tries to stay one frame ahead of the monitor, so when it's ready for the next frame it is
+    /// already prepared.
+    double,
+
+    /// No tearing, synchronizes rendering with monitor refresh rate, rendering frames when ready.
+    ///
+    /// Tries to stay two frames ahead of the monitor, so when it's ready for the next frame it is
+    /// already prepared.
+    triple,
+};
+
+/// Application options that can be configured at init time.
+pub const Options = struct {
+    /// The title of the window.
+    title: [*:0]const u8 = "Mach engine",
+
+    /// The width of the window.
+    width: u32 = 640,
+
+    /// The height of the window.
+    height: u32 = 480,
+
+    /// Monitor synchronization modes.
+    vsync: VSyncMode = .double,
+
+    /// GPU features required by the application.
+    required_features: ?[]gpu.Feature = null,
+
+    /// GPU limits required by the application.
+    required_limits: ?gpu.Limits = null,
+
+    /// Whether the application has a preference for low power or high performance GPU.
+    power_preference: gpu.PowerPreference = .none,
+};
+
+/// Window, events, inputs etc.
+core: Core,
+
+/// WebGPU driver - stores device, swap chains, targets and more
+gpu_driver: GpuDriver,
+
+allocator: Allocator,
+
+/// The amount of time (in seconds) that has passed since the last frame was rendered.
+///
+/// For example, if you are animating a cube which should rotate 360 degrees every second,
+/// instead of writing (360.0 / 60.0) and assuming the frame rate is 60hz, write
+/// (360.0 * engine.delta_time)
+delta_time: f64 = 0,
+delta_time_ns: u64 = 0,
+timer: std.time.Timer,
+
+pub const Core = struct {
+    internal: union {
+        window: glfw.Window,
+    },
+};
+
+pub const GpuDriver = struct {
+    device: gpu.Device,
+    backend_type: gpu.Adapter.BackendType,
+    swap_chain: ?gpu.SwapChain,
+    swap_chain_format: gpu.Texture.Format,
+
+    native_instance: gpu.NativeInstance,
+    surface: ?gpu.Surface,
+    current_desc: gpu.SwapChain.Descriptor,
+    target_desc: gpu.SwapChain.Descriptor,
+};