Allow to disable or enable high DPI scaling

An option is added to the Options dialog:

* Allow to enable high DPI scaling on Linux
* Allow to disable high DPI scaling on Windows

On macOS+retina, high DPI scaling applied automatically
and we do not show the option on macOS.

I had to duplicate the logic for parsing -settingspath,
because the code has to run before QApplication is created.

Task-number: QTCREATORBUG-20232
Change-Id: I4e94fc54391fe99e30d4778ec2a178529961eed7
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

3 files changed, 99 insertions, 30 deletions

diff --git a/src/app/main.cpp b/src/app/main.cpp
index b96d39225c5..f095e373bc7 100644
--- a/src/app/main.cpp
+++ b/src/app/main.cpp
@@ -58,6 +58,8 @@
 #include <QStandardPaths>
 #include <QTemporaryDir>
 
+#include <memory>
+
 #ifdef ENABLE_QT_BREAKPAD
 #include <qtsystemexceptionhandler.h>
 #endif
@@ -165,18 +167,6 @@ static inline int askMsgSendFailed()
                 QMessageBox::Retry);
 }
 
-static void setHighDpiEnvironmentVariable()
-{
-    static const char ENV_VAR_QT_DEVICE_PIXEL_RATIO[] = "QT_DEVICE_PIXEL_RATIO";
-    if (Utils::HostOsInfo().isWindowsHost()
-            && !qEnvironmentVariableIsSet(ENV_VAR_QT_DEVICE_PIXEL_RATIO) // legacy in 5.6, but still functional
-            && !qEnvironmentVariableIsSet("QT_AUTO_SCREEN_SCALE_FACTOR")
-            && !qEnvironmentVariableIsSet("QT_SCALE_FACTOR")
-            && !qEnvironmentVariableIsSet("QT_SCREEN_SCALE_FACTORS")) {
-        QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
-    }
-}
-
 // taken from utils/fileutils.cpp. We can not use utils here since that depends app_version.h.
 static bool copyRecursively(const QString &srcFilePath,
                             const QString &tgtFilePath)
@@ -303,6 +293,38 @@ static inline QSettings *userSettings()
     return createUserSettings();
 }
 
+static void setHighDpiEnvironmentVariable(int argc, char **argv)
+{
+
+    if (Utils::HostOsInfo().isMacHost())
+        return;
+
+    std::vector<std::string> arguments(argv, argv + argc);
+    auto it = arguments.begin();
+    QString settingsPath;
+    while (it != arguments.end()) {
+        const QString &arg = QString::fromStdString(*it);
+        it = ++it;
+        if (arg == SETTINGS_OPTION && it != arguments.end())
+            settingsPath = QDir::fromNativeSeparators(QString::fromStdString(*it));
+    }
+    if (!settingsPath.isEmpty())
+        QSettings::setPath(QSettings::IniFormat, QSettings::UserScope, settingsPath);
+    std::unique_ptr<QSettings> settings(createUserSettings());
+
+    const bool defaultValue = Utils::HostOsInfo().isWindowsHost();
+    const bool enableHighDpiScaling = settings->value("Core/EnableHighDpiScaling", defaultValue).toBool();
+
+    static const char ENV_VAR_QT_DEVICE_PIXEL_RATIO[] = "QT_DEVICE_PIXEL_RATIO";
+    if (enableHighDpiScaling
+            && !qEnvironmentVariableIsSet(ENV_VAR_QT_DEVICE_PIXEL_RATIO) // legacy in 5.6, but still functional
+            && !qEnvironmentVariableIsSet("QT_AUTO_SCREEN_SCALE_FACTOR")
+            && !qEnvironmentVariableIsSet("QT_SCALE_FACTOR")
+            && !qEnvironmentVariableIsSet("QT_SCREEN_SCALE_FACTORS")) {
+        QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    }
+}
+
 void loadFonts()
 {
     const QDir dir(resourcePath() + "/fonts/");
@@ -325,7 +347,7 @@ int main(int argc, char **argv)
 
     Utils::TemporaryDirectory::setMasterTemporaryDirectory(QDir::tempPath() + "/" + Core::Constants::IDE_CASED_ID + "-XXXXXX");
 
-    setHighDpiEnvironmentVariable();
+    setHighDpiEnvironmentVariable(argc, argv);
 
     QLoggingCategory::setFilterRules(QLatin1String("qtc.*.debug=false\nqtc.*.info=false"));
 
diff --git a/src/plugins/coreplugin/generalsettings.cpp b/src/plugins/coreplugin/generalsettings.cpp
index 2a0036616e6..f830f7c46e7 100644
--- a/src/plugins/coreplugin/generalsettings.cpp
+++ b/src/plugins/coreplugin/generalsettings.cpp
@@ -29,6 +29,7 @@
 #include "infobar.h"
 
 #include <utils/checkablemessagebox.h>
+#include <utils/hostosinfo.h>
 #include <utils/stylehelper.h>
 
 #include <QCoreApplication>
@@ -44,6 +45,8 @@ using namespace Utils;
 namespace Core {
 namespace Internal {
 
+const char settingsKeyDPI[] = "Core/EnableHighDpiScaling";
+
 GeneralSettings::GeneralSettings()
     : m_page(0), m_dialog(0)
 {
@@ -103,6 +106,19 @@ QWidget *GeneralSettings::widget()
         m_page->colorButton->setColor(StyleHelper::requestedBaseColor());
         m_page->resetWarningsButton->setEnabled(canResetWarnings());
 
+        if (Utils::HostOsInfo().isMacHost()) {
+            m_page->dpiLabel->setVisible(false);
+            m_page->dpiCheckbox->setVisible(false);
+        } else {
+            const bool defaultValue = Utils::HostOsInfo().isWindowsHost();
+            m_page->dpiCheckbox->setChecked(ICore::settings()->value(settingsKeyDPI, defaultValue).toBool());
+            connect(m_page->dpiCheckbox, &QCheckBox::toggled, this, [](bool checked) {
+                ICore::settings()->setValue(settingsKeyDPI, checked);
+                QMessageBox::information(ICore::mainWindow(), tr("Restart Required"),
+                                         tr("The high DPI settings will take effect after restart."));
+            });
+        }
+
         connect(m_page->resetColorButton, &QAbstractButton::clicked,
                 this, &GeneralSettings::resetInterfaceColor);
         connect(m_page->resetWarningsButton, &QAbstractButton::clicked,
diff --git a/src/plugins/coreplugin/generalsettings.ui b/src/plugins/coreplugin/generalsettings.ui
index 333be51ac76..0302314d645 100644
--- a/src/plugins/coreplugin/generalsettings.ui
+++ b/src/plugins/coreplugin/generalsettings.ui
@@ -24,6 +24,20 @@
         </property>
        </widget>
       </item>
+      <item row="2" column="0">
+       <widget class="QLabel" name="languageLabel">
+        <property name="text">
+         <string>Language:</string>
+        </property>
+       </widget>
+      </item>
+      <item row="1" column="0">
+       <widget class="QLabel" name="themeLabel">
+        <property name="text">
+         <string>Theme:</string>
+        </property>
+       </widget>
+      </item>
       <item row="0" column="1">
        <layout class="QHBoxLayout" name="horizontalLayout">
         <item>
@@ -70,20 +84,13 @@
         </item>
        </layout>
       </item>
-      <item row="1" column="0">
-       <widget class="QLabel" name="themeLabel">
-        <property name="text">
-         <string>Theme:</string>
+      <item row="4" column="0">
+       <widget class="QPushButton" name="resetWarningsButton">
+        <property name="toolTip">
+         <string>Re-enable warnings that were suppressed by selecting &quot;Do Not Show Again&quot; (for example, missing highlighter).</string>
         </property>
-       </widget>
-      </item>
-      <item row="1" column="1">
-       <widget class="Core::Internal::ThemeChooser" name="themeChooser" native="true"/>
-      </item>
-      <item row="2" column="0">
-       <widget class="QLabel" name="languageLabel">
         <property name="text">
-         <string>Language:</string>
+         <string comment="Button text">Reset Warnings</string>
         </property>
        </widget>
       </item>
@@ -114,13 +121,37 @@
         </item>
        </layout>
       </item>
+      <item row="1" column="1">
+       <widget class="Core::Internal::ThemeChooser" name="themeChooser" native="true"/>
+      </item>
+      <item row="3" column="1">
+       <layout class="QHBoxLayout" name="horizontalLayout_2">
+        <item>
+         <widget class="QCheckBox" name="dpiCheckbox">
+          <property name="text">
+           <string>Enable high DPI scaling</string>
+          </property>
+         </widget>
+        </item>
+        <item>
+         <spacer name="horizontalSpacer_3">
+          <property name="orientation">
+           <enum>Qt::Horizontal</enum>
+          </property>
+          <property name="sizeHint" stdset="0">
+           <size>
+            <width>285</width>
+            <height>20</height>
+           </size>
+          </property>
+         </spacer>
+        </item>
+       </layout>
+      </item>
       <item row="3" column="0">
-       <widget class="QPushButton" name="resetWarningsButton">
-        <property name="toolTip">
-         <string>Re-enable warnings that were suppressed by selecting &quot;Do Not Show Again&quot; (for example, missing highlighter).</string>
-        </property>
+       <widget class="QLabel" name="dpiLabel">
         <property name="text">
-         <string comment="Button text">Reset Warnings</string>
+         <string>High DPI scaling:</string>
         </property>
        </widget>
       </item>