app: move ownership of GPU context to app.Window

The Window creates the context, and should also be responsible for
destroying it.

As a bonus, the wrong release ordering of loop.renderLoop is fixed.
Before this change, the context would be destroyed before the renderer
got a chance to destroy its resources.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/loop.go

@@ -77,7 +77,6 @@ func (l *renderLoop) renderLoop(ctx window.Context) error {
 			return
 		}
 		defer g.Release()
-		defer ctx.Release()
 		initErr <- nil
 	loop:
 		for {

app/window.go

@@ -25,6 +25,7 @@ type Option func(opts *window.Options)
 // Window represents an operating system window.
 type Window struct {
 	driver window.Driver
+	ctx    window.Context
 	loop   *renderLoop
 
 	// driverFuncs is a channel of functions to run when
@@ -132,14 +133,14 @@ func (w *Window) validateAndProcess(frameStart time.Time, size image.Point, sync
 			}
 		}
 		if w.loop == nil {
-			var ctx window.Context
-			ctx, err := w.driver.NewContext()
+			var err error
+			w.ctx, err = w.driver.NewContext()
 			if err != nil {
 				return err
 			}
-			w.loop, err = newLoop(ctx)
+			w.loop, err = newLoop(w.ctx)
 			if err != nil {
-				ctx.Release()
+				w.ctx.Release()
 				return err
 			}
 		}
@@ -295,6 +296,10 @@ func (w *Window) destroyGPU() {
 		w.loop.Release()
 		w.loop = nil
 	}
+	if w.ctx != nil {
+		w.ctx.Release()
+		w.ctx = nil
+	}
 }
 
 // waitFrame waits for the client to either call FrameEvent.Frame