[QT] Add QtUi

For now QtUi is a stub besides
- getting the scale factor to verify things are hooked up correctly
- detecting font changes to ensure the QT event loop is working

Bug: 1317782
Change-Id: I8dec8a108ff6f877a89bdfcddc8a257476106abd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3601270
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1002866}

chrome/browser/themes/theme_service.cc

@@ -496,6 +496,8 @@ ThemeService::BrowserThemeProvider::GetColorProviderColor(int id) const {
         }
 #endif
       }
+      if (!native_theme)
+        return absl::nullopt;
 
       auto color_provider_key = native_theme->GetColorProviderKey(
           GetThemeSupplier(), delegate_->ShouldUseCustomFrame());

ui/base/BUILD.gn

@@ -18,6 +18,7 @@ import("//testing/libfuzzer/fuzzer_test.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
 import("//ui/base/ui_features.gni")
+import("//ui/qt/qt.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
@@ -83,6 +84,7 @@ buildflag_header("buildflags") {
     "HAS_NATIVE_ACCESSIBILITY=$has_native_accessibility",
     "HAS_PLATFORM_ACCESSIBILITY_SUPPORT=$has_platform_accessibility_support",
     "USE_GTK=$use_gtk",
+    "USE_QT=$use_qt",
   ]
 }
 

ui/qt/BUILD.gn

@@ -0,0 +1,83 @@
+# Copyright 2022 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/config/chromecast_build.gni")
+import("//build/config/linux/pkg_config.gni")
+import("//ui/qt/qt.gni")
+
+assert(use_qt)
+assert(is_linux)
+assert(!is_chromecast)
+
+pkg_config("qt5_config") {
+  packages = [
+    "Qt5Core",
+    "Qt5Widgets",
+  ]
+}
+
+source_set("qt_interface") {
+  visibility = [ ":*" ]
+
+  # Since `:qt` depends on `qt_shim` via data_deps, gn check would error-out
+  # if qt_interface.h was placed in `qt_shim`, so it's placed in a separate
+  # target instead.
+  public = [ "qt_interface.h" ]
+}
+
+shared_library("qt5_shim") {
+  visibility = [
+    ":qt",
+    "//chrome/installer/linux:*",
+  ]
+
+  # Since qt_shim is a shared library even in non-component builds, it shouldn't
+  # depend on any other targets since that would duplicate code between binaries
+  # leading to increased size and potential issues from duplicated global state.
+  no_default_deps = true
+  assert_no_deps = [
+    "//base",
+    "//buildtools/third_party/libc++",
+  ]
+  deps = [ ":qt_interface" ]
+
+  # It's OK to depend on the system libstdc++ since it's a dependency of QT, so
+  # it will get loaded into the process anyway.
+  libs = [ "stdc++" ]
+
+  configs += [ ":qt5_config" ]
+
+  public = []
+  sources = [
+    "qt_shim.cc",
+    "qt_shim.h",
+
+    # This file is generated to avoid a dependency on `moc` during the build.
+    # 1. $ build/linux/debian_bullseye_amd64-sysroot/usr/lib/qt5/bin/moc \
+    #      ui/qt/qt_shim.h > ui/qt/qt_shim_moc.cc
+    # 2. $ git cl format
+    # 3. Manually add copyright header.
+    "qt_shim_moc.cc",
+  ]
+}
+
+component("qt") {
+  visibility = [ "//ui/views/linux_ui:linux_ui_factory" ]
+
+  defines = [ "IS_QT_IMPL" ]
+
+  # qt_shim is in data_deps since we want to load it manually.
+  data_deps = [ ":qt5_shim" ]
+  deps = [
+    ":qt_interface",
+    "//base",
+    "//ui/shell_dialogs",
+    "//ui/views",
+  ]
+
+  sources = [
+    "qt_ui.cc",
+    "qt_ui.h",
+  ]
+}

ui/qt/DEPS

@@ -0,0 +1,5 @@
+include_rules = [
+  "+ui/gfx",
+  "+ui/shell_dialogs",
+  "+ui/views",
+]

ui/qt/OWNERS

@@ -0,0 +1,2 @@
+thestig@chromium.org
+thomasanderson@chromium.org

ui/qt/qt.gni

@@ -0,0 +1,8 @@
+# Copyright 2022 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+declare_args() {
+  # https://crbug.com/1317782 enable QT UI by default on Linux.
+  use_qt = false
+}

ui/qt/qt_interface.h

@@ -0,0 +1,28 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_QT_QT_INTERFACE_H_
+#define UI_QT_QT_INTERFACE_H_
+
+// This file shouldn't include any standard C++ headers (directly or indirectly)
+
+namespace qt {
+
+class QtInterface {
+ public:
+  QtInterface() = default;
+  QtInterface(const QtInterface&) = delete;
+  QtInterface& operator=(const QtInterface&) = delete;
+  virtual ~QtInterface() = default;
+
+  virtual double GetScaleFactor() const = 0;
+};
+
+}  // namespace qt
+
+// This should be the only thing exported from qt_shim.
+extern "C" __attribute__((visibility("default"))) qt::QtInterface*
+CreateQtInterface(int* argc, char** argv);
+
+#endif  // UI_QT_QT_INTERFACE_H_

ui/qt/qt_shim.cc

@@ -0,0 +1,32 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/qt/qt_shim.h"
+
+#include <stdio.h>
+
+#include <QApplication>
+
+namespace qt {
+
+QtShim::QtShim(int* argc, char** argv) : app_(*argc, argv) {
+  connect(&app_, SIGNAL(fontChanged(const QFont&)), this,
+          SLOT(FontChanged(const QFont&)));
+}
+
+QtShim::~QtShim() = default;
+
+double QtShim::GetScaleFactor() const {
+  return app_.devicePixelRatio();
+}
+
+void QtShim::FontChanged(const QFont& font) {
+  // TODO(thomasanderson): implement this.
+}
+
+}  // namespace qt
+
+qt::QtInterface* CreateQtInterface(int* argc, char** argv) {
+  return new qt::QtShim(argc, argv);
+}

ui/qt/qt_shim.h

@@ -0,0 +1,37 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_QT_QT_SHIM_H_
+#define UI_QT_QT_SHIM_H_
+
+#include <QApplication>
+#include <QObject>
+
+#include "ui/qt/qt_interface.h"
+
+namespace qt {
+
+// This class directly interacts with QT.  It's required to be a QObject
+// to receive signals from QT via slots.
+class QtShim : public QObject, public QtInterface {
+  Q_OBJECT
+
+ public:
+  QtShim(int* argc, char** argv);
+
+  ~QtShim() override;
+
+  // QtShim:
+  double GetScaleFactor() const override;
+
+ private slots:
+  void FontChanged(const QFont& font);
+
+ private:
+  QApplication app_;
+};
+
+}  // namespace qt
+
+#endif  // UI_QT_QT_SHIM_H_

ui/qt/qt_shim_moc.cc

@@ -0,0 +1,121 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/****************************************************************************
+** Meta object code from reading C++ file 'qt_shim.h'
+**
+** Created by: The Qt Meta Object Compiler version 67 (Qt 5.15.2)
+**
+** WARNING! All changes made in this file will be lost!
+*****************************************************************************/
+
+#include <QtCore/qbytearray.h>
+#include <QtCore/qmetatype.h>
+#include <memory>
+#include "ui/qt/qt_shim.h"
+#if !defined(Q_MOC_OUTPUT_REVISION)
+#error "The header file 'qt_shim.h' doesn't include <QObject>."
+#elif Q_MOC_OUTPUT_REVISION != 67
+#error "This file was generated using the moc from 5.15.2. It"
+#error "cannot be used with the include files from this version of Qt."
+#error "(The moc has changed too much.)"
+#endif
+
+QT_BEGIN_MOC_NAMESPACE
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_DEPRECATED
+struct qt_meta_stringdata_qt__QtShim_t {
+  QByteArrayData data[4];
+  char stringdata0[29];
+};
+#define QT_MOC_LITERAL(idx, ofs, len)                                        \
+  Q_STATIC_BYTE_ARRAY_DATA_HEADER_INITIALIZER_WITH_OFFSET(                   \
+      len, qptrdiff(offsetof(qt_meta_stringdata_qt__QtShim_t, stringdata0) + \
+                    ofs - idx * sizeof(QByteArrayData)))
+static const qt_meta_stringdata_qt__QtShim_t qt_meta_stringdata_qt__QtShim = {
+    {
+        QT_MOC_LITERAL(0, 0, 10),   // "qt::QtShim"
+        QT_MOC_LITERAL(1, 11, 11),  // "FontChanged"
+        QT_MOC_LITERAL(2, 23, 0),   // ""
+        QT_MOC_LITERAL(3, 24, 4)    // "font"
+
+    },
+    "qt::QtShim\0FontChanged\0\0font"};
+#undef QT_MOC_LITERAL
+
+static const uint qt_meta_data_qt__QtShim[] = {
+
+    // content:
+    8,      // revision
+    0,      // classname
+    0, 0,   // classinfo
+    1, 14,  // methods
+    0, 0,   // properties
+    0, 0,   // enums/sets
+    0, 0,   // constructors
+    0,      // flags
+    0,      // signalCount
+
+    // slots: name, argc, parameters, tag, flags
+    1, 1, 19, 2, 0x08 /* Private */,
+
+    // slots: parameters
+    QMetaType::Void, QMetaType::QFont, 3,
+
+    0  // eod
+};
+
+void qt::QtShim::qt_static_metacall(QObject* _o,
+                                    QMetaObject::Call _c,
+                                    int _id,
+                                    void** _a) {
+  if (_c == QMetaObject::InvokeMetaMethod) {
+    auto* _t = static_cast<QtShim*>(_o);
+    Q_UNUSED(_t)
+    switch (_id) {
+      case 0:
+        _t->FontChanged((*reinterpret_cast<const QFont(*)>(_a[1])));
+        break;
+      default:;
+    }
+  }
+}
+
+QT_INIT_METAOBJECT const QMetaObject qt::QtShim::staticMetaObject = {
+    {QMetaObject::SuperData::link<QObject::staticMetaObject>(),
+     qt_meta_stringdata_qt__QtShim.data, qt_meta_data_qt__QtShim,
+     qt_static_metacall, nullptr, nullptr}};
+
+const QMetaObject* qt::QtShim::metaObject() const {
+  return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject()
+                                    : &staticMetaObject;
+}
+
+void* qt::QtShim::qt_metacast(const char* _clname) {
+  if (!_clname)
+    return nullptr;
+  if (!strcmp(_clname, qt_meta_stringdata_qt__QtShim.stringdata0))
+    return static_cast<void*>(this);
+  if (!strcmp(_clname, "QtInterface"))
+    return static_cast<QtInterface*>(this);
+  return QObject::qt_metacast(_clname);
+}
+
+int qt::QtShim::qt_metacall(QMetaObject::Call _c, int _id, void** _a) {
+  _id = QObject::qt_metacall(_c, _id, _a);
+  if (_id < 0)
+    return _id;
+  if (_c == QMetaObject::InvokeMetaMethod) {
+    if (_id < 1)
+      qt_static_metacall(this, _c, _id, _a);
+    _id -= 1;
+  } else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
+    if (_id < 1)
+      *reinterpret_cast<int*>(_a[0]) = -1;
+    _id -= 1;
+  }
+  return _id;
+}
+QT_WARNING_POP
+QT_END_MOC_NAMESPACE