app: avoid relocking contexts every frame

Signed-off-by: Joe Julian <me@joejulian.name>

app/window.go

@@ -46,6 +46,10 @@ type Window struct {
 
 	ctx context
 	gpu gpu.GPU
+	// ctxNeedsLock tracks whether the rendering context must be made
+	// current again before the next GPU operation. Refresh paths, surface
+	// loss, and explicit unlocks all invalidate the current binding.
+	ctxNeedsLock bool
 	// timer tracks the delayed invalidate goroutine.
 	timer struct {
 		// quit is shuts down the goroutine.
@@ -146,15 +150,10 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				if err != nil {
 					return err
 				}
+				w.ctxNeedsLock = true
 				sync = true
 			}
 		}
-		if w.ctx != nil {
-			if err := w.ctx.Lock(); err != nil {
-				w.destroyGPU()
-				return err
-			}
-		}
 		if sync && w.ctx != nil {
 			if err := w.ctx.Refresh(); err != nil {
 				if errors.Is(err, errOutOfDate) {
@@ -168,11 +167,19 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				}
 				return err
 			}
+			w.ctxNeedsLock = true
+		}
+		if w.ctx != nil && w.ctxNeedsLock {
+			if err := w.ctx.Lock(); err != nil {
+				w.destroyGPU()
+				return err
+			}
+			w.ctxNeedsLock = false
 		}
 		if w.gpu == nil && !w.nocontext {
 			gpu, err := gpu.New(w.ctx.API())
 			if err != nil {
-				w.ctx.Unlock()
+				w.unlockContext()
 				w.destroyGPU()
 				return err
 			}
@@ -180,7 +187,7 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 		}
 		if w.gpu != nil {
 			if err := w.frame(frame, size); err != nil {
-				w.ctx.Unlock()
+				w.unlockContext()
 				if errors.Is(err, errOutOfDate) {
 					// GPU surface needs refreshing.
 					sync = true
@@ -200,7 +207,6 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 		var err error
 		if w.gpu != nil {
 			err = w.ctx.Present()
-			w.ctx.Unlock()
 		}
 		return err
 	}
@@ -503,16 +509,26 @@ func (c *callbacks) ActionAt(p f32.Point) (system.Action, bool) {
 	return c.w.queue.ActionAt(p)
 }
 
+func (w *Window) unlockContext() {
+	if w.ctx == nil || w.ctxNeedsLock {
+		return
+	}
+	w.ctx.Unlock()
+	w.ctxNeedsLock = true
+}
+
 func (w *Window) destroyGPU() {
 	if w.gpu != nil {
-		w.ctx.Lock()
-		w.gpu.Release()
-		w.ctx.Unlock()
+		if err := w.ctx.Lock(); err == nil {
+			w.gpu.Release()
+			w.ctx.Unlock()
+		}
 		w.gpu = nil
 	}
 	if w.ctx != nil {
 		w.ctx.Release()
 		w.ctx = nil
+		w.ctxNeedsLock = false
 	}
 }
 
@@ -655,10 +671,12 @@ func (w *Window) processEvent(e event.Event) bool {
 		w.coalesced.destroy = &e2
 	case ViewEvent:
 		if !e2.Valid() && w.gpu != nil {
-			w.ctx.Lock()
-			w.gpu.Release()
+			if err := w.ctx.Lock(); err == nil {
+				w.gpu.Release()
+				w.ctx.Unlock()
+			}
 			w.gpu = nil
-			w.ctx.Unlock()
+			w.ctxNeedsLock = true
 		}
 		w.coalesced.view = &e2
 	case ConfigEvent:

app/window_test.go

@@ -11,18 +11,40 @@ import (
 	"gioui.org/op"
 )
 
-func TestValidateAndProcessLocksBeforeRefresh(t *testing.T) {
+func TestValidateAndProcessRelocksAfterRefresh(t *testing.T) {
 	ctx := &testContext{}
 	w := &Window{
-		ctx: ctx,
-		gpu: &testGPU{},
+		ctx:          ctx,
+		gpu:          &testGPU{},
+		ctxNeedsLock: false,
 	}
 
 	if err := w.validateAndProcess(image.Pt(320, 240), true, new(op.Ops), nil); err != nil {
 		t.Fatalf("validateAndProcess returned error: %v", err)
 	}
 
-	want := []string{"lock", "refresh", "render-target", "present", "unlock"}
+	want := []string{"refresh", "lock", "render-target", "present"}
+	if got := ctx.ops; !equalStringSlices(got, want) {
+		t.Fatalf("unexpected call order:\n got  %v\n want %v", got, want)
+	}
+	if w.ctxNeedsLock {
+		t.Fatalf("context should remain current after a successful frame")
+	}
+}
+
+func TestValidateAndProcessSkipsRedundantRelock(t *testing.T) {
+	ctx := &testContext{}
+	w := &Window{
+		ctx:          ctx,
+		gpu:          &testGPU{},
+		ctxNeedsLock: false,
+	}
+
+	if err := w.validateAndProcess(image.Pt(320, 240), false, new(op.Ops), nil); err != nil {
+		t.Fatalf("validateAndProcess returned error: %v", err)
+	}
+
+	want := []string{"render-target", "present"}
 	if got := ctx.ops; !equalStringSlices(got, want) {
 		t.Fatalf("unexpected call order:\n got  %v\n want %v", got, want)
 	}