Adjust outgoing bubble text and icon colors.

Telegram/SourceFiles/ui/chat/chat_style.cpp

@@ -472,6 +472,8 @@ void ChatStyle::assignPalette(not_null<const style::palette*> palette) {
 	_msgBotKbOverBgAddCorners = {};
 	_msgSelectOverlayCornersSmall = {};
 	_msgSelectOverlayCornersLarge = {};
+
+	_paletteChanged.fire({});
 }
 
 const CornersPixmaps &ChatStyle::serviceBgCornersNormal() const {
@@ -616,6 +618,17 @@ void ChatStyle::make(
 	make(my.ripple.color, original.ripple.color);
 }
 
+void ChatStyle::make(
+		style::ScrollArea &my,
+		const style::ScrollArea &original) const {
+	my = original;
+	make(my.bg, original.bg);
+	make(my.bgOver, original.bgOver);
+	make(my.barBg, original.barBg);
+	make(my.barBgOver, original.barBgOver);
+	make(my.shColor, original.shColor);
+}
+
 template <typename Type>
 void ChatStyle::make(
 		Type MessageStyle::*my,

Telegram/SourceFiles/ui/chat/chat_style.h

@@ -15,6 +15,7 @@ enum class ImageRoundRadius;
 
 namespace style {
 struct TwoIconButton;
+struct ScrollArea;
 } // namespace style
 
 namespace Ui {
@@ -138,6 +139,10 @@ public:
 
 	void apply(not_null<ChatTheme*> theme);
 
+	[[nodiscard]] rpl::producer<> paletteChanged() const {
+		return _paletteChanged.events();
+	}
+
 	template <typename Type>
 	[[nodiscard]] Type value(const Type &original) const {
 		auto my = Type();
@@ -145,6 +150,15 @@ public:
 		return my;
 	}
 
+	template <typename Type>
+	[[nodiscard]] const Type &value(
+			rpl::lifetime &parentLifetime,
+			const Type &original) const {
+		const auto my = parentLifetime.make_state<Type>();
+		make(*my, original);
+		return *my;
+	}
+
 	[[nodiscard]] const CornersPixmaps &serviceBgCornersNormal() const;
 	[[nodiscard]] const CornersPixmaps &serviceBgCornersInverted() const;
 
@@ -241,6 +255,9 @@ private:
 	void make(
 		style::TwoIconButton &my,
 		const style::TwoIconButton &original) const;
+	void make(
+		style::ScrollArea &my,
+		const style::ScrollArea &original) const;
 
 	[[nodiscard]] MessageStyle &messageStyleRaw(
 		bool outbg,
@@ -303,6 +320,8 @@ private:
 	style::icon _historyPollChoiceRight = { Qt::Uninitialized };
 	style::icon _historyPollChoiceWrong = { Qt::Uninitialized };
 
+	rpl::event_stream<> _paletteChanged;
+
 	rpl::lifetime _defaultPaletteChangeLifetime;
 
 };

Telegram/SourceFiles/ui/chat/chat_theme.cpp

@@ -25,6 +25,8 @@ constexpr auto kCacheBackgroundFastTimeout = crl::time(200);
 constexpr auto kBackgroundFadeDuration = crl::time(200);
 constexpr auto kMinimumTiledSize = 512;
 constexpr auto kMaxSize = 2960;
+constexpr auto kMaxContrastValue = 21.;
+constexpr auto kMinAcceptableContrast = 1.14;// 4.5;
 
 [[nodiscard]] QColor DefaultBackgroundColor() {
 	return QColor(213, 223, 233);
@@ -133,6 +135,25 @@ constexpr auto kMaxSize = 2960;
 	return Images::GenerateLinearGradient(QSize(kSize, kSize), data.colors);
 }
 
+// https://stackoverflow.com/a/9733420
+[[nodiscard]] float64 CountContrast(const QColor &a, const QColor &b) {
+	const auto luminance = [](const QColor &c) {
+		const auto map = [](double value) {
+			return (value <= 0.03928)
+				? (value / 12.92)
+				: std::pow((value + 0.055) / 1.055, 2.4);
+		};
+		return map(c.redF()) * 0.2126
+			+ map(c.greenF()) * 0.7152
+			+ map(c.blueF()) * 0.0722;
+	};
+	const auto luminance1 = luminance(a);
+	const auto luminance2 = luminance(b);
+	const auto brightest = std::max(luminance1, luminance2);
+	const auto darkest = std::min(luminance1, luminance2);
+	return (brightest + 0.05) / (darkest + 0.05);
+}
+
 } // namespace
 
 bool operator==(const ChatThemeBackground &a, const ChatThemeBackground &b) {
@@ -201,7 +222,7 @@ void ChatTheme::adjustPalette(const ChatThemeDescriptor &descriptor) {
 	}
 	const auto bubblesAccent = descriptor.bubblesData.accent
 		? descriptor.bubblesData.accent
-		: !descriptor.bubblesData.colors.empty()
+		: (!descriptor.bubblesData.colors.empty())
 		? ThemeAdjustedColor(
 			p.msgOutReplyBarColor()->c,
 			CountAverageColor(descriptor.bubblesData.colors))
@@ -230,6 +251,55 @@ void ChatTheme::adjustPalette(const ChatThemeDescriptor &descriptor) {
 		adjust(p.historyCallArrowOutFg(), by);
 		adjust(p.historyFileOutIconFg(), by);
 	}
+	auto outBgColors = descriptor.bubblesData.colors;
+	if (outBgColors.empty()) {
+		outBgColors.push_back(p.msgOutBg()->c);
+	}
+	const auto colors = {
+		p.msgOutServiceFg(),
+		p.msgOutDateFg(),
+		p.msgFileThumbLinkOutFg(),
+		p.msgFileOutBg(),
+		p.msgOutReplyBarColor(),
+		p.msgWaveformOutActive(),
+		p.historyTextOutFg(),
+		p.mediaOutFg(),
+		p.historyLinkOutFg(),
+		p.msgOutMonoFg(),
+		p.historyOutIconFg(),
+		p.historyCallArrowOutFg(),
+	};
+	const auto minimal = [&](const QColor &with) {
+		auto result = kMaxContrastValue;
+		for (const auto &color : colors) {
+			result = std::min(result, CountContrast(color->c, with));
+		}
+		return result;
+	};
+	const auto withBg = [&](auto &&count) {
+		auto result = kMaxContrastValue;
+		for (const auto &bg : outBgColors) {
+			result = std::min(result, count(bg));
+		}
+		return result;
+	};
+	const auto singleWithBg = [&](const QColor &c) {
+		return withBg([&](const QColor &with) {
+			return CountContrast(c, with);
+		});
+	};
+	if (withBg(minimal) < kMinAcceptableContrast) {
+		const auto white = QColor(255, 255, 255);
+		const auto black = QColor(0, 0, 0);
+		// This one always gives black :)
+		//const auto now = (singleWithBg(white) >= singleWithBg(black))
+		//	? white
+		//	: black;
+		const auto now = descriptor.basedOnDark ? white : black;
+		for (const auto &color : colors) {
+			set(color, now);
+		}
+	}
 }
 
 void ChatTheme::set(const style::color &my, const QColor &color) {

Telegram/SourceFiles/ui/chat/chat_theme.h

@@ -101,6 +101,7 @@ struct ChatThemeDescriptor {
 	Fn<void(style::palette&)> preparePalette;
 	ChatThemeBackgroundData backgroundData;
 	ChatThemeBubblesData bubblesData;
+	bool basedOnDark = false;
 };
 
 class ChatTheme final : public base::has_weak_ptr {