engine: add render pass / encoder / queue management

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/engine.zig

@@ -9,20 +9,34 @@ const allocator = gpa.allocator();
 /// The main Mach engine ECS module.
 pub const Engine = struct {
     device: *gpu.Device,
+    queue: *gpu.Queue,
     exit: bool,
+    pass: *gpu.RenderPassEncoder,
+    encoder: *gpu.CommandEncoder,
 
     pub const name = .engine;
 
     pub fn engineInit(world: *World) !void {
         core.allocator = allocator;
         try core.init(.{});
-        world.mod.engine.state.device = core.device;
+        const state = &world.mod.engine.state;
-        world.mod.engine.state.exit = false;
+        state.device = core.device;
+        state.queue = core.device.getQueue();
+        state.exit = false;
+        state.encoder = state.device.createCommandEncoder(&gpu.CommandEncoder.Descriptor{
+            .label = "engine.state.encoder",
+        });
 
         try world.send(.init, .{});
     }
 
-    pub fn engineDeinit(world: *World) !void {
+    pub fn engineDeinit(
+        world: *World,
+        engine: *World.Mod(.engine),
+    ) !void {
+        // TODO: this triggers a device loss error, which we should handle correctly
+        // engine.state.device.release();
+        engine.state.queue.release();
         try world.send(.deinit, .{});
         core.deinit();
         world.deinit();
@@ -33,6 +47,48 @@ pub const Engine = struct {
         try world.send(.exit, .{});
         world.mod.engine.state.exit = true;
     }
+
+    pub fn engineBeginPass(
+        engine: *World.Mod(.engine),
+        clear_color: gpu.Color,
+    ) !void {
+        const back_buffer_view = core.swap_chain.getCurrentTextureView().?;
+        defer back_buffer_view.release();
+
+        // TODO: expose options
+        const color_attachment = gpu.RenderPassColorAttachment{
+            .view = back_buffer_view,
+            .clear_value = clear_color,
+            .load_op = .clear,
+            .store_op = .store,
+        };
+        const pass_info = gpu.RenderPassDescriptor.init(.{
+            .color_attachments = &.{color_attachment},
+        });
+
+        engine.state.pass = engine.state.encoder.beginRenderPass(&pass_info);
+    }
+
+    pub fn engineEndPass(
+        engine: *World.Mod(.engine),
+    ) !void {
+        // End this pass
+        engine.state.pass.end();
+        engine.state.pass.release();
+
+        var command = engine.state.encoder.finish(null);
+        defer command.release();
+        engine.state.queue.submit(&[_]*gpu.CommandBuffer{command});
+
+        // Prepare for next pass
+        engine.state.encoder = engine.state.device.createCommandEncoder(&gpu.CommandEncoder.Descriptor{
+            .label = "engine.state.encoder",
+        });
+    }
+
+    pub fn enginePresent() !void {
+        core.swap_chain.present();
+    }
 };
 
 pub const App = struct {