1 files changed, 173 insertions, 0 deletions
diff --git a/widget/ScrollbarDrawingWin.cpp b/widget/ScrollbarDrawingWin.cpp
new file mode 100644
index 0000000000..c2d85ae671
--- /dev/null
+++ b/widget/ScrollbarDrawingWin.cpp
@@ -0,0 +1,173 @@
+/* -*- Mode: C++; tab-width: 40; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ScrollbarDrawingWin.h"
+
+#include "mozilla/gfx/Helpers.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/StaticPrefs_widget.h"
+#include "nsLayoutUtils.h"
+#include "Theme.h"
+#include "nsNativeTheme.h"
+
+namespace mozilla::widget {
+
+LayoutDeviceIntSize ScrollbarDrawingWin::GetMinimumWidgetSize(
+    nsPresContext* aPresContext, StyleAppearance aAppearance,
+    nsIFrame* aFrame) {
+  MOZ_ASSERT(nsNativeTheme::IsWidgetScrollbarPart(aAppearance));
+
+  switch (aAppearance) {
+    case StyleAppearance::ScrollbarbuttonUp:
+    case StyleAppearance::ScrollbarbuttonDown:
+    case StyleAppearance::ScrollbarbuttonLeft:
+    case StyleAppearance::ScrollbarbuttonRight:
+      // For scrollbar-width:thin, we don't display the buttons.
+      if (IsScrollbarWidthThin(aFrame)) {
+        return LayoutDeviceIntSize{};
+      }
+      [[fallthrough]];
+    case StyleAppearance::ScrollbarVertical:
+    case StyleAppearance::ScrollbarHorizontal:
+    case StyleAppearance::ScrollbarthumbVertical:
+    case StyleAppearance::ScrollbarthumbHorizontal: {
+      // TODO: for short scrollbars it could be nice if the thumb could shrink
+      // under this size.
+      auto relevantSize = GetScrollbarSize(aPresContext, aFrame);
+      const bool isHorizontal =
+          aAppearance == StyleAppearance::ScrollbarHorizontal ||
+          aAppearance == StyleAppearance::ScrollbarthumbHorizontal ||
+          aAppearance == StyleAppearance::ScrollbarbuttonLeft ||
+          aAppearance == StyleAppearance::ScrollbarbuttonRight;
+      auto size = LayoutDeviceIntSize{relevantSize, relevantSize};
+      if (aAppearance == StyleAppearance::ScrollbarHorizontal ||
+          aAppearance == StyleAppearance::ScrollbarVertical) {
+        // Always reserve some space in the right direction. Historically we've
+        // reserved 2 times the size in the other axis (for the buttons).
+        // We do this even when painting thin scrollbars just for consistency,
+        // though there just one would probably do there.
+        if (isHorizontal) {
+          size.width *= 2;
+        } else {
+          size.height *= 2;
+        }
+      }
+      return size;
+    }
+    default:
+      return LayoutDeviceIntSize{};
+  }
+}
+
+// Returns the style for custom scrollbar if the scrollbar part frame should
+// use the custom drawing path, nullptr otherwise.
+const ComputedStyle* GetCustomScrollbarStyle(nsIFrame* aFrame) {
+  const ComputedStyle* style = nsLayoutUtils::StyleForScrollbar(aFrame);
+  if (style->StyleUI()->HasCustomScrollbars() ||
+      ScrollbarDrawing::IsScrollbarWidthThin(*style)) {
+    return style;
+  }
+  bool useDarkScrollbar = !StaticPrefs::widget_disable_dark_scrollbar() &&
+                          nsNativeTheme::IsDarkBackgroundForScrollbar(aFrame);
+  if (useDarkScrollbar) {
+    return style;
+  }
+  return nullptr;
+}
+
+Maybe<nsITheme::Transparency> ScrollbarDrawingWin::GetScrollbarPartTransparency(
+    nsIFrame* aFrame, StyleAppearance aAppearance) {
+  if (nsNativeTheme::IsWidgetScrollbarPart(aAppearance)) {
+    if (const ComputedStyle* style = GetCustomScrollbarStyle(aFrame)) {
+      auto* ui = style->StyleUI();
+      if (ui->mScrollbarColor.IsAuto() ||
+          ui->mScrollbarColor.AsColors().track.MaybeTransparent()) {
+        return Some(nsITheme::eTransparent);
+      }
+      // These widgets may be thinner than the track, so we need to return
+      // transparent for them to make the track visible.
+      switch (aAppearance) {
+        case StyleAppearance::ScrollbarthumbHorizontal:
+        case StyleAppearance::ScrollbarthumbVertical:
+        case StyleAppearance::ScrollbarbuttonUp:
+        case StyleAppearance::ScrollbarbuttonDown:
+        case StyleAppearance::ScrollbarbuttonLeft:
+        case StyleAppearance::ScrollbarbuttonRight:
+          return Some(nsITheme::eTransparent);
+        default:
+          break;
+      }
+    }
+    if (aFrame->PresContext()->UseOverlayScrollbars()) {
+      return Some(nsITheme::eTransparent);
+    }
+  }
+
+  switch (aAppearance) {
+    case StyleAppearance::ScrollbarHorizontal:
+    case StyleAppearance::ScrollbarVertical:
+    case StyleAppearance::Scrollcorner:
+      // Knowing that scrollbars and statusbars are opaque improves
+      // performance, because we create layers for them. This better be
+      // true across all Windows themes! If it's not true, we should
+      // paint an opaque background for them to make it true!
+      // TODO(emilio): Unclear how much this optimization matters in practice
+      // now we're in a WR-only world.
+      return Some(nsITheme::eOpaque);
+    default:
+      break;
+  }
+
+  return Nothing();
+}
+
+template <typename PaintBackendData>
+bool ScrollbarDrawingWin::DoPaintScrollbarThumb(
+    PaintBackendData& aPaintData, const LayoutDeviceRect& aRect,
+    ScrollbarKind aScrollbarKind, nsIFrame* aFrame, const ComputedStyle& aStyle,
+    const ElementState& aElementState, const DocumentState& aDocumentState,
+    const Colors& aColors, const DPIRatio& aDpiRatio) {
+  sRGBColor thumbColor = ComputeScrollbarThumbColor(
+      aFrame, aStyle, aElementState, aDocumentState, aColors);
+  ThemeDrawing::FillRect(aPaintData, aRect, thumbColor);
+  return true;
+}
+
+bool ScrollbarDrawingWin::PaintScrollbarThumb(
+    DrawTarget& aDrawTarget, const LayoutDeviceRect& aRect,
+    ScrollbarKind aScrollbarKind, nsIFrame* aFrame, const ComputedStyle& aStyle,
+    const ElementState& aElementState, const DocumentState& aDocumentState,
+    const Colors& aColors, const DPIRatio& aDpiRatio) {
+  return DoPaintScrollbarThumb(aDrawTarget, aRect, aScrollbarKind, aFrame,
+                               aStyle, aElementState, aDocumentState, aColors,
+                               aDpiRatio);
+}
+
+bool ScrollbarDrawingWin::PaintScrollbarThumb(
+    WebRenderBackendData& aWrData, const LayoutDeviceRect& aRect,
+    ScrollbarKind aScrollbarKind, nsIFrame* aFrame, const ComputedStyle& aStyle,
+    const ElementState& aElementState, const DocumentState& aDocumentState,
+    const Colors& aColors, const DPIRatio& aDpiRatio) {
+  return DoPaintScrollbarThumb(aWrData, aRect, aScrollbarKind, aFrame, aStyle,
+                               aElementState, aDocumentState, aColors,
+                               aDpiRatio);
+}
+
+void ScrollbarDrawingWin::RecomputeScrollbarParams() {
+  uint32_t defaultSize = kDefaultWinScrollbarSize;
+  uint32_t overrideSize =
+      StaticPrefs::widget_non_native_theme_scrollbar_size_override();
+  if (overrideSize > 0) {
+    defaultSize = overrideSize;
+  }
+  ConfigureScrollbarSize(defaultSize);
+
+  if (StaticPrefs::widget_non_native_theme_win_scrollbar_use_system_size()) {
+    ConfigureScrollbarSize(LookAndFeel::GetInt(
+        LookAndFeel::IntID::SystemScrollbarSize, defaultSize));
+  }
+}
+
+}  // namespace mozilla::widget