Use Qt's High-DPI scaling on Windows (#4868)

src/widgets/helper/Button.cpp

@@ -8,26 +8,44 @@
 #include <QPainter>
 #include <QScreen>
 
-namespace chatterino {
 namespace {
 
-    // returns a new resized image or the old one if the size didn't change
-    auto resizePixmap(const QPixmap &current, const QPixmap resized,
-                      const QSize &size) -> QPixmap
+QSizeF deviceIndependentSize(const QPixmap &pixmap)
+{
+#if QT_VERSION < QT_VERSION_CHECK(6, 2, 0)
+    return QSizeF(pixmap.width(), pixmap.height()) / pixmap.devicePixelRatio();
+#else
+    return pixmap.deviceIndependentSize();
+#endif
+}
+
+/**
+ * Resizes a pixmap to a desired size.
+ * Does nothing if the target pixmap is already sized correctly.
+ * 
+ * @param target The target pixmap.
+ * @param source The unscaled pixmap.
+ * @param size The desired device independent size.
+ * @param dpr The device pixel ratio of the target area. The size of the target in pixels will be `size * dpr`.
+ */
+void resizePixmap(QPixmap &target, const QPixmap &source, const QSize &size,
+                  qreal dpr)
+{
+    if (deviceIndependentSize(target) == size)
     {
-        if (resized.size() == size)
-        {
-            return resized;
-        }
-        else
-        {
-            return current.scaled(size, Qt::IgnoreAspectRatio,
-                                  Qt::SmoothTransformation);
-        }
+        return;
     }
 
+    QPixmap resized = source;
+    resized.setDevicePixelRatio(dpr);
+    target = resized.scaled(size * dpr, Qt::IgnoreAspectRatio,
+                            Qt::SmoothTransformation);
+}
+
 }  // namespace
 
+namespace chatterino {
+
 Button::Button(BaseWidget *parent)
     : BaseWidget(parent)
 {
@@ -47,6 +65,12 @@ void Button::setMouseEffectColor(std::optional<QColor> color)
 
 void Button::setPixmap(const QPixmap &_pixmap)
 {
+    // Avoid updates if the pixmap didn't change
+    if (_pixmap.cacheKey() == this->pixmap_.cacheKey())
+    {
+        return;
+    }
+
     this->pixmap_ = _pixmap;
     this->resizedPixmap_ = {};
     this->update();
@@ -158,8 +182,8 @@ void Button::paintButton(QPainter &painter)
 
         QRect rect = this->rect();
 
-        this->resizedPixmap_ =
-            resizePixmap(this->pixmap_, this->resizedPixmap_, rect.size());
+        resizePixmap(this->resizedPixmap_, this->pixmap_, rect.size(),
+                     this->devicePixelRatio());
 
         int margin = this->height() < 22 * this->scale() ? 3 : 6;
 

src/widgets/helper/ChannelView.cpp

@@ -615,7 +615,7 @@ void ChannelView::scaleChangedEvent(float scale)
 
     if (this->goToBottom_)
     {
-        auto factor = this->qtFontScale();
+        auto factor = this->scale();
 #ifdef Q_OS_MACOS
         factor = scale * 80.F /
                  std::max<float>(
@@ -703,8 +703,10 @@ void ChannelView::layoutVisibleMessages(
         {
             const auto &message = messages[i];
 
-            redrawRequired |= message->layout(layoutWidth, this->scale(), flags,
-                                              this->bufferInvalidationQueued_);
+            redrawRequired |= message->layout(
+                layoutWidth, this->scale(),
+                this->scale() * static_cast<float>(this->devicePixelRatio()),
+                flags, this->bufferInvalidationQueued_);
 
             y += message->getHeight();
         }
@@ -738,7 +740,10 @@ void ChannelView::updateScrollbar(
     {
         auto *message = messages[i].get();
 
-        message->layout(layoutWidth, this->scale(), flags, false);
+        message->layout(
+            layoutWidth, this->scale(),
+            this->scale() * static_cast<float>(this->devicePixelRatio()), flags,
+            false);
 
         h -= message->getHeight();
 
@@ -1720,9 +1725,11 @@ void ChannelView::wheelEvent(QWheelEvent *event)
                 }
                 else
                 {
-                    snapshot[i - 1]->layout(this->getLayoutWidth(),
-                                            this->scale(), this->getFlags(),
-                                            false);
+                    snapshot[i - 1]->layout(
+                        this->getLayoutWidth(), this->scale(),
+                        this->scale() *
+                            static_cast<float>(this->devicePixelRatio()),
+                        this->getFlags(), false);
                     scrollFactor = 1;
                     currentScrollLeft = snapshot[i - 1]->getHeight();
                 }
@@ -1755,9 +1762,11 @@ void ChannelView::wheelEvent(QWheelEvent *event)
                 }
                 else
                 {
-                    snapshot[i + 1]->layout(this->getLayoutWidth(),
-                                            this->scale(), this->getFlags(),
-                                            false);
+                    snapshot[i + 1]->layout(
+                        this->getLayoutWidth(), this->scale(),
+                        this->scale() *
+                            static_cast<float>(this->devicePixelRatio()),
+                        this->getFlags(), false);
 
                     scrollFactor = 1;
                     currentScrollLeft = snapshot[i + 1]->getHeight();

src/widgets/helper/NotebookTab.cpp

@@ -27,15 +27,6 @@
 
 namespace chatterino {
 namespace {
-    qreal deviceDpi(QWidget *widget)
-    {
-#ifdef Q_OS_WIN
-        return widget->devicePixelRatioF();
-#else
-        return 1.0;
-#endif
-    }
-
     // Translates the given rectangle by an amount in the direction to appear like the tab is selected.
     // For example, if location is Top, the rectangle will be translated in the negative Y direction,
     // or "up" on the screen, by amount.
@@ -196,8 +187,8 @@ int NotebookTab::normalTabWidth()
     float scale = this->scale();
     int width;
 
-    auto metrics = getIApp()->getFonts()->getFontMetrics(
-        FontStyle::UiTabs, float(qreal(this->scale()) * deviceDpi(this)));
+    QFontMetrics metrics =
+        getIApp()->getFonts()->getFontMetrics(FontStyle::UiTabs, scale);
 
     if (this->hasXButton())
     {
@@ -439,11 +430,9 @@ void NotebookTab::paintEvent(QPaintEvent *)
     QPainter painter(this);
     float scale = this->scale();
 
-    auto div = std::max<float>(0.01f, this->logicalDpiX() * deviceDpi(this));
-    painter.setFont(
-        getIApp()->getFonts()->getFont(FontStyle::UiTabs, scale * 96.f / div));
+    painter.setFont(app->getFonts()->getFont(FontStyle::UiTabs, scale));
     QFontMetrics metrics =
-        app->getFonts()->getFontMetrics(FontStyle::UiTabs, scale * 96.f / div);
+        app->getFonts()->getFontMetrics(FontStyle::UiTabs, scale);
 
     int height = int(scale * NOTEBOOK_TAB_HEIGHT);