Add a cross-platform frameless window example

Written in pure Qt. Cross-platform.
Lacking the system features on Windows of course.

Signed-off-by: Yuhang Zhao <2546789017@qq.com>

examples/QWidget2/QWidget2.pro

@@ -0,0 +1,6 @@
+TARGET = QWidget2
+TEMPLATE = app
+QT += widgets
+HEADERS += widget.h
+SOURCES += widget.cpp main.cpp
+include($$PWD/../common.pri)

examples/QWidget2/main.cpp

@@ -0,0 +1,63 @@
+/*
+ * MIT License
+ *
+ * Copyright (C) 2020 by wangwenx190 (Yuhang Zhao)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "widget.h"
+#include <QApplication>
+#include <QStyleOption>
+
+int main(int argc, char *argv[])
+{
+    QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);
+    // High DPI scaling is enabled by default from Qt 6
+#if (QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
+    // Windows: we are using the manifest file to get maximum compatibility
+    // because some APIs are not supprted on old systems such as Windows 7
+    // and Windows 8. And once we have set the DPI awareness level in the
+    // manifest file, any attemptation to try to change it through API will
+    // fail. In other words, Qt won't be able to enable or disable high DPI
+    // scaling or change the DPI awareness level once we have set it in the
+    // manifest file. So the following two lines are uesless actually (However,
+    // they are still useful on other platforms).
+    QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
+    // Don't round the scale factor.
+    // This will break QWidget applications because they can't render correctly.
+    // Qt Quick applications won't have this issue.
+    QGuiApplication::setHighDpiScaleFactorRoundingPolicy(
+        Qt::HighDpiScaleFactorRoundingPolicy::PassThrough);
+#endif
+#endif
+
+    QApplication application(argc, argv);
+    Widget widget;
+    QStyleOption option;
+    option.initFrom(&widget);
+    const QIcon icon = widget.style()->standardIcon(QStyle::SP_ComputerIcon, &option);
+    widget.setWindowIcon(icon);
+    widget.setWindowTitle(QObject::tr("Hello, World!"));
+    widget.resize(800, 600);
+    widget.show();
+    return QApplication::exec();
+}

examples/QWidget2/widget.cpp

@@ -0,0 +1,259 @@
+/*
+ * MIT License
+ *
+ * Copyright (C) 2020 by wangwenx190 (Yuhang Zhao)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "widget.h"
+#include "../../framelesshelper.h"
+#include <QEvent>
+#include <QGraphicsDropShadowEffect>
+#include <QHBoxLayout>
+#include <QLabel>
+#include <QPainter>
+#include <QPushButton>
+#include <QSpacerItem>
+#include <QVBoxLayout>
+
+Q_GLOBAL_STATIC(FramelessHelper, framelessHelper)
+
+ContentsWidget::ContentsWidget(QWidget *parent) : QWidget(parent)
+{
+    setAttribute(Qt::WA_StyledBackground);
+}
+
+void ContentsWidget::setShouldDrawWindowBorder(const bool val)
+{
+    m_bShouldDrawWindowBorder = val;
+    update();
+}
+
+bool ContentsWidget::getShouldDrawWindowBorder() const
+{
+    return m_bShouldDrawWindowBorder;
+}
+
+void ContentsWidget::paintEvent(QPaintEvent *event)
+{
+    QWidget::paintEvent(event);
+    if (m_bShouldDrawWindowBorder) {
+        QPainter painter(this);
+        painter.save();
+        painter.setPen({Qt::black, 1.5});
+        painter.drawLine(0, 0, width(), 0);
+        painter.drawLine(0, height(), width(), height());
+        painter.drawLine(0, 0, 0, height());
+        painter.drawLine(width(), 0, width(), height());
+        painter.restore();
+    }
+}
+
+Widget::Widget(QWidget *parent) : QWidget(parent)
+{
+    titleBarHeight = framelessHelper()->getTitleBarHeight();
+    createWinId();
+    setupUi();
+    initBackgroundWindow();
+    installEventFilter(this);
+}
+
+bool Widget::isNormal() const
+{
+    return (!isMinimized() && !isMaximized() && !isFullScreen());
+}
+
+void Widget::setupUi()
+{
+    contentsWidget = new ContentsWidget(this);
+    contentsWidget->setObjectName(QLatin1String("contentsWidget"));
+    contentsWidget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
+    const QSize systemButtonSize = {qRound(titleBarHeight * 1.5), titleBarHeight};
+    const QSize systemIconSize = {17, 17};
+    titleBarWidget = new QWidget(contentsWidget);
+    titleBarWidget->setObjectName(QLatin1String("titleBarWidget"));
+    titleBarWidget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
+    titleBarWidget->setFixedHeight(titleBarHeight);
+    windowIconButton = new QPushButton(this);
+    windowIconButton->setObjectName(QLatin1String("windowIconButton"));
+    windowIconButton->setFixedSize(systemIconSize);
+    windowIconButton->setIconSize(systemIconSize);
+    connect(this, &Widget::windowIconChanged, windowIconButton, &QPushButton::setIcon);
+    windowTitleLabel = new QLabel(this);
+    QFont f = font();
+    f.setPointSizeF(8.63);
+    windowTitleLabel->setFont(f);
+    connect(this, &Widget::windowTitleChanged, windowTitleLabel, &QLabel::setText);
+    minimizeButton = new QPushButton(this);
+    minimizeButton->setObjectName(QLatin1String("minimizeButton"));
+    minimizeButton->setFixedSize(systemButtonSize);
+    minimizeButton->setIconSize(systemButtonSize);
+    minimizeButton->setIcon(QIcon(QLatin1String(":/images/button_minimize_black.svg")));
+    connect(minimizeButton, &QPushButton::clicked, this, &Widget::showMinimized);
+    maximizeButton = new QPushButton(this);
+    maximizeButton->setObjectName(QLatin1String("maximizeButton"));
+    maximizeButton->setFixedSize(systemButtonSize);
+    maximizeButton->setIconSize(systemButtonSize);
+    maximizeButton->setIcon(QIcon(QLatin1String(":/images/button_maximize_black.svg")));
+    connect(maximizeButton, &QPushButton::clicked, this, [this]() {
+        if (isMaximized()) {
+            showNormal();
+        } else {
+            showMaximized();
+        }
+    });
+    closeButton = new QPushButton(this);
+    closeButton->setObjectName(QLatin1String("closeButton"));
+    closeButton->setFixedSize(systemButtonSize);
+    closeButton->setIconSize(systemButtonSize);
+    closeButton->setIcon(QIcon(QLatin1String(":/images/button_close_black.svg")));
+    connect(closeButton, &QPushButton::clicked, this, &Widget::close);
+    const auto titleBarWidgetLayout = new QHBoxLayout(titleBarWidget);
+    titleBarWidgetLayout->setSpacing(0);
+    titleBarWidgetLayout->setContentsMargins(0, 0, 0, 0);
+    titleBarWidgetLayout->addSpacerItem(
+        new QSpacerItem(7, 20, QSizePolicy::Fixed, QSizePolicy::Fixed));
+    titleBarWidgetLayout->addWidget(windowIconButton);
+    titleBarWidgetLayout->addSpacerItem(
+        new QSpacerItem(3, 20, QSizePolicy::Fixed, QSizePolicy::Fixed));
+    titleBarWidgetLayout->addWidget(windowTitleLabel);
+    titleBarWidgetLayout->addStretch();
+    titleBarWidgetLayout->addWidget(minimizeButton);
+    titleBarWidgetLayout->addWidget(maximizeButton);
+    titleBarWidgetLayout->addWidget(closeButton);
+    titleBarWidget->setLayout(titleBarWidgetLayout);
+    const auto contentsWidgetLayout = new QVBoxLayout(contentsWidget);
+    contentsWidgetLayout->setSpacing(0);
+    contentsWidgetLayout->setContentsMargins(1, 1, 1, 0);
+    contentsWidgetLayout->addWidget(titleBarWidget);
+    contentsWidgetLayout->addStretch();
+    contentsWidget->setLayout(contentsWidgetLayout);
+    const auto backgroundWindowLayout = new QVBoxLayout(this);
+    backgroundWindowLayout->setSpacing(0);
+    backgroundWindowLayout->addWidget(contentsWidget);
+    setLayout(backgroundWindowLayout);
+    setStyleSheet(QLatin1String(R"(
+#contentsWidget {
+  background-color: #f0f0f0;
+}
+
+#titleBarWidget {
+  background-color: white;
+}
+
+#windowIconButton, #minimizeButton, #maximizeButton, #closeButton {
+  border-style: none;
+  background-color: transparent;
+}
+
+#minimizeButton:hover, #maximizeButton:hover {
+  background-color: #80c7c7c7;
+}
+
+#minimizeButton:pressed, #maximizeButton:pressed {
+  background-color: #80808080;
+}
+
+#closeButton:hover {
+  background-color: #e81123;
+}
+
+#closeButton:pressed {
+  background-color: #8c0a15;
+}
+)"));
+}
+
+void Widget::initBackgroundWindow()
+{
+    QWindow *win = windowHandle();
+    framelessHelper()->removeWindowFrame(win);
+    framelessHelper()->addIgnoreObject(win, windowIconButton);
+    framelessHelper()->addIgnoreObject(win, minimizeButton);
+    framelessHelper()->addIgnoreObject(win, maximizeButton);
+    framelessHelper()->addIgnoreObject(win, closeButton);
+    framelessHelper()->setTitleBarHeight(titleBarHeight + framelessHelper()->getBorderHeight());
+    //setAttribute(Qt::WA_Hover);
+    setAttribute(Qt::WA_NoSystemBackground);
+    setAttribute(Qt::WA_TranslucentBackground);
+    shadowEffect = new QGraphicsDropShadowEffect(this);
+    shadowEffect->setOffset(0, 0);
+    contentsWidget->setGraphicsEffect(shadowEffect);
+    setFrameShadowEnabled();
+    setFrameShadowActive();
+}
+
+void Widget::setFrameShadowEnabled(const bool enable)
+{
+    if (enable) {
+        const int bw = framelessHelper()->getBorderWidth();
+        const int bh = framelessHelper()->getBorderHeight();
+        layout()->setContentsMargins(bw, bh, bw, bh);
+        shadowEffect->setEnabled(true);
+    } else {
+        shadowEffect->setEnabled(false);
+        layout()->setContentsMargins(0, 0, 0, 0);
+    }
+}
+
+void Widget::setFrameShadowActive(const bool active)
+{
+    if (active) {
+        shadowEffect->setColor({0, 0, 0, 80});
+        shadowEffect->setBlurRadius(25);
+    } else {
+        shadowEffect->setColor({0, 0, 0, 60});
+        shadowEffect->setBlurRadius(20);
+    }
+}
+
+bool Widget::eventFilter(QObject *object, QEvent *event)
+{
+    Q_ASSERT(object);
+    Q_ASSERT(event);
+    if (object == this) {
+        switch (event->type()) {
+        case QEvent::WindowStateChange: {
+            const bool normal = isNormal();
+            contentsWidget->setShouldDrawWindowBorder(normal);
+            setFrameShadowEnabled(normal);
+            framelessHelper()->setTitleBarHeight(
+                titleBarHeight + (normal ? framelessHelper()->getBorderHeight() : 0));
+            const QLatin1String maxIconPath = QLatin1String{":/images/button_maximize_black.svg"};
+            const QLatin1String restoreIconPath = QLatin1String{
+                ":/images/button_restore_black.svg"};
+            maximizeButton->setIcon(QIcon(normal ? maxIconPath : restoreIconPath));
+        } break;
+        case QEvent::WindowActivate: {
+            if (isNormal()) {
+                setFrameShadowActive();
+            }
+        } break;
+        case QEvent::WindowDeactivate: {
+            if (isNormal()) {
+                setFrameShadowActive(false);
+            }
+        } break;
+        default:
+            break;
+        }
+    }
+    return QWidget::eventFilter(object, event);
+}

examples/QWidget2/widget.h

@@ -0,0 +1,82 @@
+/*
+ * MIT License
+ *
+ * Copyright (C) 2020 by wangwenx190 (Yuhang Zhao)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#pragma once
+
+#include <QWidget>
+
+class QGraphicsDropShadowEffect;
+class QPushButton;
+class QLabel;
+
+class ContentsWidget : public QWidget
+{
+    Q_OBJECT
+    Q_DISABLE_COPY_MOVE(ContentsWidget)
+
+public:
+    explicit ContentsWidget(QWidget *parent = nullptr);
+    ~ContentsWidget() override = default;
+
+    void setShouldDrawWindowBorder(const bool val);
+    bool getShouldDrawWindowBorder() const;
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+
+private:
+    bool m_bShouldDrawWindowBorder = true;
+};
+
+class Widget : public QWidget
+{
+    Q_OBJECT
+    Q_DISABLE_COPY_MOVE(Widget)
+
+public:
+    explicit Widget(QWidget *parent = nullptr);
+    ~Widget() override = default;
+
+    bool isNormal() const;
+
+protected:
+    bool eventFilter(QObject *object, QEvent *event) override;
+
+private:
+    void setupUi();
+    void initBackgroundWindow();
+    void setFrameShadowEnabled(const bool enable = true);
+    void setFrameShadowActive(const bool active = true);
+
+private:
+    int titleBarHeight = 30;
+    ContentsWidget *contentsWidget = nullptr;
+    QGraphicsDropShadowEffect *shadowEffect = nullptr;
+    QWidget *titleBarWidget = nullptr;
+    QPushButton *windowIconButton = nullptr;
+    QLabel *windowTitleLabel = nullptr;
+    QPushButton *minimizeButton = nullptr;
+    QPushButton *maximizeButton = nullptr;
+    QPushButton *closeButton = nullptr;
+};

examples/Win32Demo/widget.cpp

@@ -175,12 +175,12 @@ void Widget::setupUi()
     horizontalLayout->setSpacing(0);
     horizontalLayout->setContentsMargins(0, 0, 0, 0);
     horizontalSpacer_7 = new QSpacerItem(3, 20, QSizePolicy::Fixed, QSizePolicy::Minimum);
-    horizontalLayout->addItem(horizontalSpacer_7);
+    horizontalLayout->addSpacerItem(horizontalSpacer_7);
     iconButton = new QPushButton(titleBarWidget);
     iconButton->setObjectName(QLatin1String("iconButton"));
     horizontalLayout->addWidget(iconButton);
     horizontalSpacer = new QSpacerItem(3, 20, QSizePolicy::Fixed, QSizePolicy::Minimum);
-    horizontalLayout->addItem(horizontalSpacer);
+    horizontalLayout->addSpacerItem(horizontalSpacer);
     titleLabel = new QLabel(titleBarWidget);
     titleLabel->setObjectName(QLatin1String("titleLabel"));
     QFont font;
@@ -188,7 +188,7 @@ void Widget::setupUi()
     titleLabel->setFont(font);
     horizontalLayout->addWidget(titleLabel);
     horizontalSpacer_2 = new QSpacerItem(40, 20, QSizePolicy::Expanding, QSizePolicy::Minimum);
-    horizontalLayout->addItem(horizontalSpacer_2);
+    horizontalLayout->addSpacerItem(horizontalSpacer_2);
     minimizeButton = new QPushButton(titleBarWidget);
     minimizeButton->setObjectName(QLatin1String("minimizeButton"));
     QSizePolicy sizePolicy1(QSizePolicy::Fixed, QSizePolicy::Fixed);
@@ -235,10 +235,10 @@ void Widget::setupUi()
     contentsWidget->setSizePolicy(sizePolicy2);
     verticalLayout_2 = new QVBoxLayout(contentsWidget);
     verticalSpacer_2 = new QSpacerItem(20, 40, QSizePolicy::Minimum, QSizePolicy::Expanding);
-    verticalLayout_2->addItem(verticalSpacer_2);
+    verticalLayout_2->addSpacerItem(verticalSpacer_2);
     horizontalLayout_2 = new QHBoxLayout();
     horizontalSpacer_3 = new QSpacerItem(40, 20, QSizePolicy::Expanding, QSizePolicy::Minimum);
-    horizontalLayout_2->addItem(horizontalSpacer_3);
+    horizontalLayout_2->addSpacerItem(horizontalSpacer_3);
     controlPanelWidget = new QWidget(contentsWidget);
     QSizePolicy sizePolicy3(QSizePolicy::Maximum, QSizePolicy::Maximum);
     sizePolicy3.setHorizontalStretch(0);
@@ -275,18 +275,18 @@ void Widget::setupUi()
     verticalLayout->addWidget(resizableCB);
     horizontalLayout_2->addWidget(controlPanelWidget);
     horizontalSpacer_4 = new QSpacerItem(40, 20, QSizePolicy::Expanding, QSizePolicy::Minimum);
-    horizontalLayout_2->addItem(horizontalSpacer_4);
+    horizontalLayout_2->addSpacerItem(horizontalSpacer_4);
     verticalLayout_2->addLayout(horizontalLayout_2);
     verticalSpacer = new QSpacerItem(20, 40, QSizePolicy::Minimum, QSizePolicy::Expanding);
-    verticalLayout_2->addItem(verticalSpacer);
+    verticalLayout_2->addSpacerItem(verticalSpacer);
     horizontalLayout_3 = new QHBoxLayout();
     horizontalSpacer_5 = new QSpacerItem(40, 20, QSizePolicy::Expanding, QSizePolicy::Minimum);
-    horizontalLayout_3->addItem(horizontalSpacer_5);
+    horizontalLayout_3->addSpacerItem(horizontalSpacer_5);
     moveCenterButton = new QPushButton(contentsWidget);
     moveCenterButton->setFont(font1);
     horizontalLayout_3->addWidget(moveCenterButton);
     horizontalSpacer_6 = new QSpacerItem(40, 20, QSizePolicy::Expanding, QSizePolicy::Minimum);
-    horizontalLayout_3->addItem(horizontalSpacer_6);
+    horizontalLayout_3->addSpacerItem(horizontalSpacer_6);
     verticalLayout_2->addLayout(horizontalLayout_3);
     verticalLayout_3->addWidget(contentsWidget);
     if (shouldDrawBorder()) {
@@ -425,7 +425,7 @@ void Widget::paintEvent(QPaintEvent *event)
     if (shouldDrawBorder()) {
         QPainter painter(this);
         painter.save();
-        painter.setPen({borderColor(), 2.0});
+        painter.setPen({borderColor(), 1.5});
         painter.drawLine(0, 0, width(), 0);
         painter.drawLine(0, height(), width(), height());
         painter.drawLine(0, 0, 0, height());

examples/examples.pro

@@ -1,5 +1,5 @@
 TEMPLATE = subdirs
 CONFIG -= ordered
-qtHaveModule(widgets): SUBDIRS += QWidget QMainWindow
+qtHaveModule(widgets): SUBDIRS += QWidget QWidget2 QMainWindow
 qtHaveModule(quick): SUBDIRS += Quick
 win32: qtHaveModule(widgets): SUBDIRS += Win32Demo

framelesshelper.cpp

@@ -217,7 +217,8 @@ void FramelessHelper::setTitleBarEnabled(const QWindow *window, const bool val)
 void FramelessHelper::removeWindowFrame(QWindow *window, const bool center)
 {
     Q_ASSERT(window);
-    window->setFlags(window->flags() | Qt::FramelessWindowHint);
+    window->setFlags(Qt::Window | Qt::FramelessWindowHint | Qt::WindowSystemMenuHint
+                     | Qt::WindowMinMaxButtonsHint | Qt::WindowTitleHint);
     // MouseTracking is always enabled for QWindow.
     window->installEventFilter(this);
     if (center) {