3 files changed, 62 insertions(+), 6 deletions(-)

M app/gl_js.go
M app/os_js.go
M internal/gl/gl_js.go

@@ 13,6 13,7 @@ import (
 type glContext struct {
 	ctx js.Value
 	cnv js.Value
+	w   *window
 }
 
 func newContext(w *window) (*glContext, error) {


@@ 32,11 33,15 @@ func newContext(w *window) (*glContext, error) {
 	c := &glContext{
 		ctx: ctx,
 		cnv: w.cnv,
+		w:   w,
 	}
 	return c, nil
 }
 
 func (c *glContext) RenderTarget() (gpu.RenderTarget, error) {
+	if c.w.contextStatus != contextStatusOkay {
+		return nil, gpu.ErrDeviceLost
+	}
 	return gpu.OpenGLRenderTarget{}, nil
 }
 


@@ 48,9 53,6 @@ func (c *glContext) Release() {
 }
 
 func (c *glContext) Present() error {
-	if c.ctx.Call("isContextLost").Bool() {
-		return errors.New("context lost")
-	}
 	return nil
 }
 


@@ 61,7 63,15 @@ func (c *glContext) Lock() error {
 func (c *glContext) Unlock() {}
 
 func (c *glContext) Refresh() error {
-	return nil
+	switch c.w.contextStatus {
+	case contextStatusLost:
+		return errOutOfDate
+	case contextStatusRestored:
+		c.w.contextStatus = contextStatusOkay
+		return gpu.ErrDeviceLost
+	default:
+		return nil
+	}
 }
 
 func (w *window) NewContext() (context, error) {

@@ 24,6 24,14 @@ import (
 
 type ViewEvent struct{}
 
+type contextStatus int
+
+const (
+	contextStatusOkay contextStatus = iota
+	contextStatusLost
+	contextStatusRestored
+)
+
 type window struct {
 	window                js.Value
 	document              js.Value


@@ 54,6 62,8 @@ type window struct {
 	// is pending.
 	animRequested bool
 	wakeups       chan struct{}
+
+	contextStatus contextStatus
 }
 
 func newWindow(win *callbacks, options []Option) error {


@@ 162,9 172,25 @@ func (w *window) cleanup() {
 }
 
 func (w *window) addEventListeners() {
+	w.addEventListener(w.cnv, "webglcontextlost", func(this js.Value, args []js.Value) interface{} {
+		args[0].Call("preventDefault")
+		w.contextStatus = contextStatusLost
+		return nil
+	})
+	w.addEventListener(w.cnv, "webglcontextrestored", func(this js.Value, args []js.Value) interface{} {
+		args[0].Call("preventDefault")
+		w.contextStatus = contextStatusRestored
+
+		// Resize is required to force update the canvas content when restored.
+		w.cnv.Set("width", 0)
+		w.cnv.Set("height", 0)
+		w.resize()
+		w.requestRedraw()
+		return nil
+	})
 	w.addEventListener(w.visualViewport, "resize", func(this js.Value, args []js.Value) interface{} {
 		w.resize()
-		w.chanRedraw <- struct{}{}
+		w.requestRedraw()
 		return nil
 	})
 	w.addEventListener(w.window, "contextmenu", func(this js.Value, args []js.Value) interface{} {


@@ 622,10 648,14 @@ func (w *window) resize() {
 }
 
 func (w *window) draw(sync bool) {
+	if w.contextStatus == contextStatusLost {
+		return
+	}
 	size, insets, metric := w.getConfig()
 	if metric == (unit.Metric{}) || size.X == 0 || size.Y == 0 {
 		return
 	}
+
 	w.w.Event(frameEvent{
 		FrameEvent: system.FrameEvent{
 			Now:    time.Now(),


@@ 696,6 726,13 @@ func (w *window) navigationColor(c color.NRGBA) {
 	theme.Set("content", fmt.Sprintf("#%06X", []uint8{rgba.R, rgba.G, rgba.B}))
 }
 
+func (w *window) requestRedraw() {
+	select {
+	case w.chanRedraw <- struct{}{}:
+	default:
+	}
+}
+
 func osMain() {
 	select {}
 }

@@ 299,7 299,12 @@ func (f *Functions) BufferSubData(target Enum, offset int, src []byte) {
 	f._bufferSubData.Invoke(int(target), offset, f.byteArrayOf(src))
 }
 func (f *Functions) CheckFramebufferStatus(target Enum) Enum {
-	return Enum(f._checkFramebufferStatus.Invoke(int(target)).Int())
+	status := Enum(f._checkFramebufferStatus.Invoke(int(target)).Int())
+	if status != FRAMEBUFFER_COMPLETE && f.Ctx.Call("isContextLost").Bool() {
+		// If the context is lost, we say that everything is fine. That saves internal/opengl/opengl.go from panic.
+		return FRAMEBUFFER_COMPLETE
+	}
+	return status
 }
 func (f *Functions) Clear(mask Enum) {
 	f._clear.Invoke(int(mask))


@@ 633,6 638,10 @@ func paramVal(v js.Value) int {
 		}
 	case js.TypeNumber:
 		return v.Int()
+	case js.TypeUndefined:
+		return 0
+	case js.TypeNull:
+		return 0
 	default:
 		panic("unknown parameter type")
 	}