core/window: premultiply background colors

Apparently these are supposed to be premultiplied. Some docs would be nice.

Author: outfoxxed

src/core/proxywindow.cpp

@@ -287,16 +287,23 @@ QuickshellScreenInfo* ProxyWindowBase::screen() const {
 	return QuickshellTracked::instance()->screenInfo(qscreen);
 }
 
-QColor ProxyWindowBase::color() const {
-	if (this->window == nullptr) return this->mColor;
-	else return this->window->color();
-}
+QColor ProxyWindowBase::color() const { return this->mColor; }
 
 void ProxyWindowBase::setColor(QColor color) {
+	this->mColor = color;
+
 	if (this->window == nullptr) {
-		this->mColor = color;
-		emit this->colorChanged();
-	} else this->window->setColor(color);
+		if (color != this->mColor) emit this->colorChanged();
+	} else {
+		auto premultiplied = QColor::fromRgbF(
+		    color.redF() * color.alphaF(),
+		    color.greenF() * color.alphaF(),
+		    color.blueF() * color.alphaF(),
+		    color.alphaF()
+		);
+
+		this->window->setColor(premultiplied);
+	}
 }
 
 PendingRegion* ProxyWindowBase::mask() const { return this->mMask; }

src/core/windowinterface.hpp

@@ -46,20 +46,6 @@ class WindowInterface: public Reloadable {
 	/// along with map[To|From]Item (which is not reactive).
 	Q_PROPERTY(QObject* windowTransform READ windowTransform NOTIFY windowTransformChanged);
 	/// The background color of the window. Defaults to white.
-	///
-	/// > [!WARNING] This seems to behave weirdly when using transparent colors on some systems.
-	/// > Using a colored content item over a transparent window is the recommended way to work around this:
-	/// > ```qml
-	/// > ProxyWindow {
-	/// >   color: "transparent"
-	/// >   Rectangle {
-	/// >     anchors.fill: parent
-	/// >     color: "#20ffffff"
-	/// >
-	/// >     // your content here
-	/// >   }
-	/// > }
-	/// > ```
 	Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY colorChanged);
 	/// The clickthrough mask. Defaults to null.
 	///