app: avoid relocking contexts every frame

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

app/gl_ios.go

@@ -115,9 +115,6 @@ func (c *context) Unlock() {
 }
 
 func (c *context) Refresh() error {
-	if C.gio_makeCurrent(c.ctx) == 0 {
-		return errors.New("[EAGLContext setCurrentContext] failed")
-	}
 	if !c.init {
 		c.init = true
 		c.frameBuffer = c.c.CreateFramebuffer()

app/os.go

@@ -169,6 +169,7 @@ type context interface {
 	API() gpu.API
 	RenderTarget() (gpu.RenderTarget, error)
 	Present() error
+	// Refresh assumes the context is already locked and current.
 	Refresh() error
 	Release()
 	Lock() error

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.
@@ -146,6 +150,7 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				if err != nil {
 					return err
 				}
+				w.ctxNeedsLock = true
 				sync = true
 			}
 		}
@@ -162,17 +167,19 @@ func (w *Window) validateAndProcess(size image.Point, sync bool, frame *op.Ops,
 				}
 				return err
 			}
+			w.ctxNeedsLock = true
 		}
-		if w.ctx != nil {
+		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

@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package app
+
+import (
+	"image"
+	"image/color"
+	"testing"
+
+	"gioui.org/gpu"
+	"gioui.org/op"
+)
+
+func TestValidateAndProcessRelocksAfterRefresh(t *testing.T) {
+	ctx := &testContext{}
+	w := &Window{
+		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{"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)
+	}
+}
+
+type testContext struct {
+	ops []string
+}
+
+func (c *testContext) API() gpu.API {
+	return nil
+}
+
+func (c *testContext) RenderTarget() (gpu.RenderTarget, error) {
+	c.ops = append(c.ops, "render-target")
+	return gpu.OpenGLRenderTarget{}, nil
+}
+
+func (c *testContext) Present() error {
+	c.ops = append(c.ops, "present")
+	return nil
+}
+
+func (c *testContext) Refresh() error {
+	c.ops = append(c.ops, "refresh")
+	return nil
+}
+
+func (c *testContext) Release() {}
+
+func (c *testContext) Lock() error {
+	c.ops = append(c.ops, "lock")
+	return nil
+}
+
+func (c *testContext) Unlock() {
+	c.ops = append(c.ops, "unlock")
+}
+
+type testGPU struct{}
+
+func (g *testGPU) Release() {}
+
+func (g *testGPU) Clear(color.NRGBA) {}
+
+func (g *testGPU) Frame(*op.Ops, gpu.RenderTarget, image.Point) error {
+	return nil
+}
+
+func equalStringSlices(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}