fix(cef): keep browser canvas white, move anti-flash to presentation layer

Dark-theme users saw light-mode sites (e.g. ollama.com) render dark text
on a near-black canvas: the theme background was baked into
BrowserSettings.BackgroundColor, Chromium's fallback canvas for pages
that declare no background, and CEF has no runtime API to reset it (the
JS ResetBackgroundToDefault only clears an inline style).

BrowserSettings.BackgroundColor is now always opaque white, matching the
standard browser contract. The anti-white-flash moves to the
presentation layer: a theme-colored CSS provider guards the render
widget until the first accelerated paint, then tears down.

commit: 1dc7dd40311570c10609d9afdaa58e18780a3d6a
author: brice · 3mo ago · 2026-07-21 04:55 UTC
parent: 3b318d2
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email

5 files · +149 -21

A internal/infrastructure/cef/background_guard.go +106 -0

@@ -0,0 +1,106 @@
	1	+	package cef
	2	+
	3	+	import (
	4	+	"fmt"
	5	+
	6	+	"github.com/bnema/puregotk/v4/gdk"
	7	+	"github.com/bnema/puregotk/v4/gtk"
	8	+	)
	9	+
	10	+	// opaqueWhiteBackground is Chromium's standard windowless canvas fallback. It is
	11	+	// baked into every BrowserSettings.BackgroundColor so pages that paint nothing
	12	+	// get an opaque white canvas (never a theme-dark one). A zero value must not be
	13	+	// used: in windowless/OSR mode a zero-alpha background enables transparent
	14	+	// painting, which this engine does not want.
	15	+	const opaqueWhiteBackground uint32 = 0xFFFFFFFF
	16	+
	17	+	// flashGuardCSSClassPrefix scopes each WebView's transient background provider to
	18	+	// its own render widget so guards from different tabs never collide.
	19	+	const flashGuardCSSClassPrefix = "dumber-cef-flash-guard-"
	20	+
	21	+	// colorByteMask isolates a single 8-bit channel from a packed ARGB value.
	22	+	const colorByteMask = 0xFF
	23	+
	24	+	// applyBackgroundFlashGuard paints the theme background color behind the CEF
	25	+	// render widget until the first frame is presented. It is the presentation-layer
	26	+	// replacement for the former dark BrowserSettings.BackgroundColor: Chromium's
	27	+	// canvas is now always opaque white, so the anti-white-flash lives here instead.
	28	+	// The bridge widget (a GtkPicture/GtkGLArea) renders its CSS background until an
	29	+	// opaque frame texture covers it, at which point markFirstFramePainted tears the
	30	+	// guard down. Must run on the GTK main thread.
	31	+	func (wv WebView) applyBackgroundFlashGuard(widget gtk.Widget) {
	32	+	if wv == nil \|\| widget == nil {
	33	+	return
	34	+	}
	35	+	argb := wv.backgroundColor
	36	+	if argb == 0 {
	37	+	return // No theme color configured; nothing to guard against.
	38	+	}
	39	+	display := gdk.DisplayGetDefault()
	40	+	if display == nil {
	41	+	return
	42	+	}
	43	+
	44	+	a := float64((argb>>24)&colorByteMask) / colorScale
	45	+	r := (argb >> 16) & colorByteMask
	46	+	g := (argb >> 8) & colorByteMask
	47	+	b := argb & colorByteMask
	48	+	class := fmt.Sprintf("%s%d", flashGuardCSSClassPrefix, uint64(wv.id))
	49	+	css := fmt.Sprintf(".%s { background-color: rgba(%d, %d, %d, %.4f); }", class, r, g, b, a)
	50	+
	51	+	provider := gtk.NewCssProvider()
	52	+	if provider == nil {
	53	+	return
	54	+	}
	55	+	provider.LoadFromString(css)
	56	+
	57	+	wv.bgGuardMu.Lock()
	58	+	defer wv.bgGuardMu.Unlock()
	59	+	if wv.firstFramePainted.Load() {
	60	+	return // First frame already arrived before the guard could be installed.
	61	+	}
	62	+	widget.AddCssClass(class)
	63	+	gtk.StyleContextAddProviderForDisplay(display, provider, uint(gtk.STYLE_PROVIDER_PRIORITY_APPLICATION))
	64	+	wv.bgGuardProvider = provider
	65	+	wv.bgGuardWidget = widget
	66	+	wv.bgGuardClass = class
	67	+	}
	68	+
	69	+	// markFirstFramePainted records that the first CEF frame has been presented and
	70	+	// schedules teardown of the background flash guard so later frames render
	71	+	// normally. Safe to call from any thread and idempotent.
	72	+	func (wv *WebView) markFirstFramePainted() {
	73	+	if wv == nil \|\| !wv.firstFramePainted.CompareAndSwap(false, true) {
	74	+	return
	75	+	}
	76	+	wv.runOnGTK(func() {
	77	+	wv.removeBackgroundFlashGuard()
	78	+	})
	79	+	}
	80	+
	81	+	// removeBackgroundFlashGuard detaches the transient theme-background provider and
	82	+	// clears the render widget's guard class. Must run on the GTK main thread. It is
	83	+	// safe to call when no guard is installed.
	84	+	func (wv *WebView) removeBackgroundFlashGuard() {
	85	+	if wv == nil {
	86	+	return
	87	+	}
	88	+	wv.bgGuardMu.Lock()
	89	+	provider := wv.bgGuardProvider
	90	+	widget := wv.bgGuardWidget
	91	+	class := wv.bgGuardClass
	92	+	wv.bgGuardProvider = nil
	93	+	wv.bgGuardWidget = nil
	94	+	wv.bgGuardClass = ""
	95	+	wv.bgGuardMu.Unlock()
	96	+
	97	+	if provider == nil {
	98	+	return
	99	+	}
	100	+	if widget != nil && class != "" {
	101	+	widget.RemoveCssClass(class)
	102	+	}
	103	+	if display := gdk.DisplayGetDefault(); display != nil {
	104	+	gtk.StyleContextRemoveProviderForDisplay(display, provider)
	105	+	}
	106	+	}

@@ -0,0 +1,106 @@
	1	+	package cef
	2	+
	3	+	import (
	4	+	"fmt"
	5	+
	6	+	"github.com/bnema/puregotk/v4/gdk"
	7	+	"github.com/bnema/puregotk/v4/gtk"
	8	+	)
	9	+
	10	+	// opaqueWhiteBackground is Chromium's standard windowless canvas fallback. It is
	11	+	// baked into every BrowserSettings.BackgroundColor so pages that paint nothing
	12	+	// get an opaque white canvas (never a theme-dark one). A zero value must not be
	13	+	// used: in windowless/OSR mode a zero-alpha background enables transparent
	14	+	// painting, which this engine does not want.
	15	+	const opaqueWhiteBackground uint32 = 0xFFFFFFFF
	16	+
	17	+	// flashGuardCSSClassPrefix scopes each WebView's transient background provider to
	18	+	// its own render widget so guards from different tabs never collide.
	19	+	const flashGuardCSSClassPrefix = "dumber-cef-flash-guard-"
	20	+
	21	+	// colorByteMask isolates a single 8-bit channel from a packed ARGB value.
	22	+	const colorByteMask = 0xFF
	23	+
	24	+	// applyBackgroundFlashGuard paints the theme background color behind the CEF
	25	+	// render widget until the first frame is presented. It is the presentation-layer
	26	+	// replacement for the former dark BrowserSettings.BackgroundColor: Chromium's
	27	+	// canvas is now always opaque white, so the anti-white-flash lives here instead.
	28	+	// The bridge widget (a GtkPicture/GtkGLArea) renders its CSS background until an
	29	+	// opaque frame texture covers it, at which point markFirstFramePainted tears the
	30	+	// guard down. Must run on the GTK main thread.
	31	+	func (wv WebView) applyBackgroundFlashGuard(widget gtk.Widget) {
	32	+	if wv == nil \|\| widget == nil {
	33	+	return
	34	+	}
	35	+	argb := wv.backgroundColor
	36	+	if argb == 0 {
	37	+	return // No theme color configured; nothing to guard against.
	38	+	}
	39	+	display := gdk.DisplayGetDefault()
	40	+	if display == nil {
	41	+	return
	42	+	}
	43	+
	44	+	a := float64((argb>>24)&colorByteMask) / colorScale
	45	+	r := (argb >> 16) & colorByteMask
	46	+	g := (argb >> 8) & colorByteMask
	47	+	b := argb & colorByteMask
	48	+	class := fmt.Sprintf("%s%d", flashGuardCSSClassPrefix, uint64(wv.id))
	49	+	css := fmt.Sprintf(".%s { background-color: rgba(%d, %d, %d, %.4f); }", class, r, g, b, a)
	50	+
	51	+	provider := gtk.NewCssProvider()
	52	+	if provider == nil {
	53	+	return
	54	+	}
	55	+	provider.LoadFromString(css)
	56	+
	57	+	wv.bgGuardMu.Lock()
	58	+	defer wv.bgGuardMu.Unlock()
	59	+	if wv.firstFramePainted.Load() {
	60	+	return // First frame already arrived before the guard could be installed.
	61	+	}
	62	+	widget.AddCssClass(class)
	63	+	gtk.StyleContextAddProviderForDisplay(display, provider, uint(gtk.STYLE_PROVIDER_PRIORITY_APPLICATION))
	64	+	wv.bgGuardProvider = provider
	65	+	wv.bgGuardWidget = widget
	66	+	wv.bgGuardClass = class
	67	+	}
	68	+
	69	+	// markFirstFramePainted records that the first CEF frame has been presented and
	70	+	// schedules teardown of the background flash guard so later frames render
	71	+	// normally. Safe to call from any thread and idempotent.
	72	+	func (wv *WebView) markFirstFramePainted() {
	73	+	if wv == nil \|\| !wv.firstFramePainted.CompareAndSwap(false, true) {
	74	+	return
	75	+	}
	76	+	wv.runOnGTK(func() {
	77	+	wv.removeBackgroundFlashGuard()
	78	+	})
	79	+	}
	80	+
	81	+	// removeBackgroundFlashGuard detaches the transient theme-background provider and
	82	+	// clears the render widget's guard class. Must run on the GTK main thread. It is
	83	+	// safe to call when no guard is installed.
	84	+	func (wv *WebView) removeBackgroundFlashGuard() {
	85	+	if wv == nil {
	86	+	return
	87	+	}
	88	+	wv.bgGuardMu.Lock()
	89	+	provider := wv.bgGuardProvider
	90	+	widget := wv.bgGuardWidget
	91	+	class := wv.bgGuardClass
	92	+	wv.bgGuardProvider = nil
	93	+	wv.bgGuardWidget = nil
	94	+	wv.bgGuardClass = ""
	95	+	wv.bgGuardMu.Unlock()
	96	+
	97	+	if provider == nil {
	98	+	return
	99	+	}
	100	+	if widget != nil && class != "" {
	101	+	widget.RemoveCssClass(class)
	102	+	}
	103	+	if display := gdk.DisplayGetDefault(); display != nil {
	104	+	gtk.StyleContextRemoveProviderForDisplay(display, provider)
	105	+	}
	106	+	}

M internal/infrastructure/cef/factory.go +12 -8


@@ -27,7 +27,7 @@ type WebViewFactory struct {
27	27		windowlessFrameRate int32
28	28		windowlessFrameRateMax int32
29	29		inputConfig RuntimeInputConfig
30		-	bgColor atomic.Uint32 // packed ARGB for BrowserSettings.BackgroundColor
	30	+	bgColor atomic.Uint32 // packed ARGB theme color for the presentation-layer flash guard
31	31		audioOutputFactory port.AudioOutputFactory
32	32		}
33	33

@@ -69,7 +69,9 @@ func newWebViewFactory(engine Engine, opts webViewFactoryOptions) WebViewFacto
69	69		}
70	70		}
71	71
72		-	// setDefaultBackgroundColor stores a packed ARGB color for new browser creation.
	72	+	// setDefaultBackgroundColor stores the packed ARGB theme color used by the
	73	+	// presentation-layer flash guard on newly-created WebViews. It no longer feeds
	74	+	// BrowserSettings.BackgroundColor, which is always opaque white.
73	75		func (f *WebViewFactory) setDefaultBackgroundColor(r, g, b, a float64) {
74	76		const s = colorScale
75	77		argb := uint32(as)<<24 \| uint32(rs)<<16 \| uint32(gs)<<8 \| uint32(bs)

@@ -96,9 +98,9 @@ func (f *WebViewFactory) Create(ctx context.Context) (port.WebView, error) {
96	98		settings := purecef.NewBrowserSettings()
97	99		cef2gtk.ConfigureBrowserSettings(&settings, cef2gtk.BrowserSettingsOptions{WindowlessFrameRate: f.windowlessFrameRate})
98	100		settings.LocalStorage = 1 // CEF_STATE_ENABLED
99		-	if bg := f.bgColor.Load(); bg != 0 {
100		-	settings.BackgroundColor = bg
101		-	}
	101	+	// Always opaque white: Chromium's standard canvas fallback. The theme
	102	+	// background is applied at the presentation layer as a flash guard instead.
	103	+	settings.BackgroundColor = opaqueWhiteBackground
102	104
103	105		// Defer browser creation until the bridge view has a non-zero size.
104	106		// CEF requires GetViewRect to return a non-empty rect, but the GL area

@@ -142,6 +144,8 @@ func (f WebViewFactory) newWebView(ctx context.Context) (WebView, error) {
142	144		wv.nativeWidget = popupRoot
143	145		}
144	146		}
	147	+	// Guard the render widget with the theme background until the first frame.
	148	+	wv.applyBackgroundFlashGuard(nativeWidget)
145	149		})
146	150		if !result.Completed() {
147	151		wv.destroyViewBridgeOnGTKAsync()

@@ -383,9 +387,9 @@ func (f *WebViewFactory) CreateRelated(ctx context.Context, parentID port.WebVie
383	387		settings := purecef.NewBrowserSettings()
384	388		cef2gtk.ConfigureBrowserSettings(&settings, cef2gtk.BrowserSettingsOptions{WindowlessFrameRate: f.windowlessFrameRate})
385	389		settings.LocalStorage = 1 // CEF_STATE_ENABLED
386		-	if bg := f.bgColor.Load(); bg != 0 {
387		-	settings.BackgroundColor = bg
388		-	}
	390	+	// Always opaque white: the theme background is applied as a presentation-layer
	391	+	// flash guard, not baked into Chromium's canvas.
	392	+	settings.BackgroundColor = opaqueWhiteBackground
389	393
390	394		if err := f.configureInitialBrowserCreation(ctx, popupWV, popupWV.client, &windowInfo, &settings, func(w, h int32) {
391	395		f.handlePopupShellInitialResize(ctx, popupWV, func(w, h int32) {

 	windowlessFrameRate         int32
 	windowlessFrameRateMax      int32
 	inputConfig                 RuntimeInputConfig
-	bgColor                     atomic.Uint32 // packed ARGB for BrowserSettings.BackgroundColor
+	bgColor                     atomic.Uint32 // packed ARGB theme color for the presentation-layer flash guard
 	audioOutputFactory          port.AudioOutputFactory
 }
 	}
 }
-// setDefaultBackgroundColor stores a packed ARGB color for new browser creation.
+// setDefaultBackgroundColor stores the packed ARGB theme color used by the
+// presentation-layer flash guard on newly-created WebViews. It no longer feeds
+// BrowserSettings.BackgroundColor, which is always opaque white.
 func (f *WebViewFactory) setDefaultBackgroundColor(r, g, b, a float64) {
 	const s = colorScale
 	argb := uint32(a*s)<<24 | uint32(r*s)<<16 | uint32(g*s)<<8 | uint32(b*s)
 	settings := purecef.NewBrowserSettings()
 	cef2gtk.ConfigureBrowserSettings(&settings, cef2gtk.BrowserSettingsOptions{WindowlessFrameRate: f.windowlessFrameRate})
 	settings.LocalStorage = 1 // CEF_STATE_ENABLED
-	if bg := f.bgColor.Load(); bg != 0 {
+	// Always opaque white: Chromium's standard canvas fallback. The theme
-		settings.BackgroundColor = bg
+	// background is applied at the presentation layer as a flash guard instead.
-	}
+	settings.BackgroundColor = opaqueWhiteBackground
 	// Defer browser creation until the bridge view has a non-zero size.
 	// CEF requires GetViewRect to return a non-empty rect, but the GL area
 				wv.nativeWidget = popupRoot
 			}
 		}
+		// Guard the render widget with the theme background until the first frame.
+		wv.applyBackgroundFlashGuard(nativeWidget)
 	})
 	if !result.Completed() {
 		wv.destroyViewBridgeOnGTKAsync()
 	settings := purecef.NewBrowserSettings()
 	cef2gtk.ConfigureBrowserSettings(&settings, cef2gtk.BrowserSettingsOptions{WindowlessFrameRate: f.windowlessFrameRate})
 	settings.LocalStorage = 1 // CEF_STATE_ENABLED
-	if bg := f.bgColor.Load(); bg != 0 {
+	// Always opaque white: the theme background is applied as a presentation-layer
-		settings.BackgroundColor = bg
+	// flash guard, not baked into Chromium's canvas.
-	}
+	settings.BackgroundColor = opaqueWhiteBackground
 	if err := f.configureInitialBrowserCreation(ctx, popupWV, popupWV.client, &windowInfo, &settings, func(w, h int32) {
 		f.handlePopupShellInitialResize(ctx, popupWV, func(w, h int32) {

M internal/infrastructure/cef/render_handler_adapter.go +9 -0


@@ -51,6 +51,15 @@ func newDumberRenderHandler(wv *WebView) purecef.RenderHandler {
51	51
52	52		var unsupportedPaintOnce sync.Once
53	53		hooks := startupPresentationHooks(activeStartupTrace())
	54	+	// Tear down the theme background flash guard once the first frame is
	55	+	// presented, without dropping the startup trace mark the bridge already set.
	56	+	firstAcceleratedPaint := hooks.OnFirstAcceleratedPaint
	57	+	hooks.OnFirstAcceleratedPaint = func() {
	58	+	if firstAcceleratedPaint != nil {
	59	+	firstAcceleratedPaint()
	60	+	}
	61	+	wv.markFirstFramePainted()
	62	+	}
54	63		hooks.OnUnsupportedPaint = func() {
55	64		unsupportedPaintOnce.Do(func() {
56	65		if wv.ctx != nil {


@@ -51,6 +51,15 @@ func newDumberRenderHandler(wv *WebView) purecef.RenderHandler {
51		51
52	var unsupportedPaintOnce sync.Once	52		var unsupportedPaintOnce sync.Once
53	hooks := startupPresentationHooks(activeStartupTrace())	53		hooks := startupPresentationHooks(activeStartupTrace())
		54	+	// Tear down the theme background flash guard once the first frame is
		55	+	// presented, without dropping the startup trace mark the bridge already set.
		56	+	firstAcceleratedPaint := hooks.OnFirstAcceleratedPaint
		57	+	hooks.OnFirstAcceleratedPaint = func() {
		58	+	if firstAcceleratedPaint != nil {
		59	+	firstAcceleratedPaint()
		60	+	}
		61	+	wv.markFirstFramePainted()
		62	+	}
54	hooks.OnUnsupportedPaint = func() {	63		hooks.OnUnsupportedPaint = func() {
55	unsupportedPaintOnce.Do(func() {	64		unsupportedPaintOnce.Do(func() {
56	if wv.ctx != nil {	65		if wv.ctx != nil {

M internal/infrastructure/cef/webview.go +20 -11


@@ -239,6 +239,18 @@ type WebView struct {
239	239		backgroundColor uint32
240	240		inputConfig RuntimeInputConfig
241	241
	242	+	// Background flash guard: a theme-colored CSS provider painted behind the
	243	+	// render widget until the first CEF frame is presented. It replaces the
	244	+	// former dark BrowserSettings.BackgroundColor anti-white-flash, whose canvas
	245	+	// is now always opaque white. State is guarded by bgGuardMu; firstFramePainted
	246	+	// gates the one-shot teardown and resets naturally when a fresh WebView is
	247	+	// created after a browser recreation.
	248	+	firstFramePainted atomic.Bool
	249	+	bgGuardMu sync.Mutex
	250	+	bgGuardProvider *gtk.CssProvider
	251	+	bgGuardWidget *gtk.Widget
	252	+	bgGuardClass string
	253	+
242	254		// Touchpad input diagnostics are debounced to avoid flooding logs while
243	255		// debugging continuous scroll streams.
244	256		touchpadNavigation *touchpadNavigationRecognizer

@@ -992,7 +1004,7 @@ func (wv *WebView) prepareNativePopup(
992	1004		prep.parent.trackPendingNativePopup(popupID, wv)
993	1005		}
994	1006
995		-	configureNativePopupWindow(windowInfo, settings, prep.frameRate, prep.backgroundColor)
	1007	+	configureNativePopupWindow(windowInfo, settings, prep.frameRate)
996	1008		clientSlot.Set(client)
997	1009		return true
998	1010		}

@@ -1007,9 +1019,8 @@ func (wv *WebView) nativePopupPreparationSnapshot() (nativePopupPreparation, boo
1007	1019		return nativePopupPreparation{}, false
1008	1020		}
1009	1021		return nativePopupPreparation{
1010		-	parent: wv.nativePopupParent,
1011		-	frameRate: wv.windowlessFrameRate,
1012		-	backgroundColor: wv.backgroundColor,
	1022	+	parent: wv.nativePopupParent,
	1023	+	frameRate: wv.windowlessFrameRate,
1013	1024		}, true
1014	1025		}
1015	1026

@@ -1045,7 +1056,6 @@ func configureNativePopupWindow(
1045	1056		windowInfo *purecef.WindowInfo,
1046	1057		settings *purecef.BrowserSettings,
1047	1058		frameRate int32,
1048		-	backgroundColor uint32,
1049	1059		) {
1050	1060		cef2gtk.ConfigureWindowInfo(windowInfo, cef2gtk.WindowInfoOptions{})
1051	1061		if externalBeginFrameEnabled() {

@@ -1056,15 +1066,13 @@ func configureNativePopupWindow(
1056	1066		}
1057	1067		cef2gtk.ConfigureBrowserSettings(settings, cef2gtk.BrowserSettingsOptions{WindowlessFrameRate: frameRate})
1058	1068		settings.LocalStorage = 1
1059		-	if backgroundColor != 0 {
1060		-	settings.BackgroundColor = backgroundColor
1061		-	}
	1069	+	// Always opaque white; the popup shell WebView carries the theme flash guard.
	1070	+	settings.BackgroundColor = opaqueWhiteBackground
1062	1071		}
1063	1072
1064	1073		type nativePopupPreparation struct {
1065		-	parent *WebView
1066		-	frameRate int32
1067		-	backgroundColor uint32
	1074	+	parent *WebView
	1075	+	frameRate int32
1068	1076		}
1069	1077
1070	1078		func (wv *WebView) handleNativePopupAborted() {

@@ -1244,6 +1252,7 @@ func (wv *WebView) destroyViewBridgeOnGTKThread() {
1244	1252		if wv == nil \|\| wv.viewBridge == nil {
1245	1253		return
1246	1254		}
	1255	+	wv.removeBackgroundFlashGuard()
1247	1256		if wv.removeSizeObserver != nil {
1248	1257		wv.removeSizeObserver()
1249	1258		wv.removeSizeObserver = nil

 	backgroundColor     uint32
 	inputConfig         RuntimeInputConfig
+	// Background flash guard: a theme-colored CSS provider painted behind the
+	// render widget until the first CEF frame is presented. It replaces the
+	// former dark BrowserSettings.BackgroundColor anti-white-flash, whose canvas
+	// is now always opaque white. State is guarded by bgGuardMu; firstFramePainted
+	// gates the one-shot teardown and resets naturally when a fresh WebView is
+	// created after a browser recreation.
+	firstFramePainted atomic.Bool
+	bgGuardMu         sync.Mutex
+	bgGuardProvider   *gtk.CssProvider
+	bgGuardWidget     *gtk.Widget
+	bgGuardClass      string
 	// Touchpad input diagnostics are debounced to avoid flooding logs while
 	// debugging continuous scroll streams.
 	touchpadNavigation *touchpadNavigationRecognizer
 		prep.parent.trackPendingNativePopup(popupID, wv)
 	}
-	configureNativePopupWindow(windowInfo, settings, prep.frameRate, prep.backgroundColor)
+	configureNativePopupWindow(windowInfo, settings, prep.frameRate)
 	clientSlot.Set(client)
 	return true
 }
 		return nativePopupPreparation{}, false
 	}
 	return nativePopupPreparation{
-		parent:          wv.nativePopupParent,
+		parent:    wv.nativePopupParent,
-		frameRate:       wv.windowlessFrameRate,
+		frameRate: wv.windowlessFrameRate,
-		backgroundColor: wv.backgroundColor,
 	}, true
 }
 	windowInfo *purecef.WindowInfo,
 	settings *purecef.BrowserSettings,
 	frameRate int32,
-	backgroundColor uint32,
 ) {
 	cef2gtk.ConfigureWindowInfo(windowInfo, cef2gtk.WindowInfoOptions{})
 	if externalBeginFrameEnabled() {
 	}
 	cef2gtk.ConfigureBrowserSettings(settings, cef2gtk.BrowserSettingsOptions{WindowlessFrameRate: frameRate})
 	settings.LocalStorage = 1
-	if backgroundColor != 0 {
+	// Always opaque white; the popup shell WebView carries the theme flash guard.
-		settings.BackgroundColor = backgroundColor
+	settings.BackgroundColor = opaqueWhiteBackground
-	}
 }
 type nativePopupPreparation struct {
-	parent          *WebView
+	parent    *WebView
-	frameRate       int32
+	frameRate int32
-	backgroundColor uint32
 }
 func (wv *WebView) handleNativePopupAborted() {
 	if wv == nil || wv.viewBridge == nil {
 		return
 	}
+	wv.removeBackgroundFlashGuard()
 	if wv.removeSizeObserver != nil {
 		wv.removeSizeObserver()
 		wv.removeSizeObserver = nil

M internal/infrastructure/cef/webview_handlers_test.go +2 -2


@@ -380,14 +380,14 @@ func TestConfigureNativePopupWindow_UsesSharedTextureWindowlessDefaults(t *testi
380	380		windowInfo := purecef.NewWindowInfo()
381	381		settings := purecef.NewBrowserSettings()
382	382
383		-	configureNativePopupWindow(&windowInfo, &settings, 72, 0xFF112233)
	383	+	configureNativePopupWindow(&windowInfo, &settings, 72)
384	384
385	385		require.Equal(t, purecef.WindowHandle(0), windowInfo.ParentWindow)
386	386		require.Equal(t, int32(1), windowInfo.WindowlessRenderingEnabled)
387	387		require.Equal(t, int32(1), windowInfo.SharedTextureEnabled)
388	388		require.Equal(t, int32(72), settings.WindowlessFrameRate)
389	389		require.Equal(t, int32(1), settings.LocalStorage)
390		-	require.Equal(t, uint32(0xFF112233), settings.BackgroundColor)
	390	+	require.Equal(t, opaqueWhiteBackground, settings.BackgroundColor)
391	391		}
392	392
393	393		func TestOnLoadStartFiresCommittedAndUpdatesURI(t *testing.T) {


@@ -380,14 +380,14 @@ func TestConfigureNativePopupWindow_UsesSharedTextureWindowlessDefaults(t *testi
380		windowInfo := purecef.NewWindowInfo()	380		windowInfo := purecef.NewWindowInfo()
381		settings := purecef.NewBrowserSettings()	381		settings := purecef.NewBrowserSettings()
382			382
383	-	configureNativePopupWindow(&windowInfo, &settings, 72, 0xFF112233)	383	+	configureNativePopupWindow(&windowInfo, &settings, 72)
384			384
385		require.Equal(t, purecef.WindowHandle(0), windowInfo.ParentWindow)	385		require.Equal(t, purecef.WindowHandle(0), windowInfo.ParentWindow)
386		require.Equal(t, int32(1), windowInfo.WindowlessRenderingEnabled)	386		require.Equal(t, int32(1), windowInfo.WindowlessRenderingEnabled)
387		require.Equal(t, int32(1), windowInfo.SharedTextureEnabled)	387		require.Equal(t, int32(1), windowInfo.SharedTextureEnabled)
388		require.Equal(t, int32(72), settings.WindowlessFrameRate)	388		require.Equal(t, int32(72), settings.WindowlessFrameRate)
389		require.Equal(t, int32(1), settings.LocalStorage)	389		require.Equal(t, int32(1), settings.LocalStorage)
390	-	require.Equal(t, uint32(0xFF112233), settings.BackgroundColor)	390	+	require.Equal(t, opaqueWhiteBackground, settings.BackgroundColor)
391		}	391		}
392			392
393		func TestOnLoadStartFiresCommittedAndUpdatesURI(t *testing.T) {	393		func TestOnLoadStartFiresCommittedAndUpdatesURI(t *testing.T) {