ScrollbarDrawingWin.cpp

/* -*- 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:
    case StyleAppearance::Statusbar:
      // 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