background_guard.go RawHistoryFolder

1package cef
2
3import (
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.
15const 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.
19const flashGuardCSSClassPrefix = "dumber-cef-flash-guard-"
20
21// colorByteMask isolates a single 8-bit channel from a packed ARGB value.
22const 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.
31func (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.
72func (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.
84func (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}