Support stereoscopic rendering with QGraphicsView

This patch adds a manual test and the required work in graphicsview and
qwidget private apis to support stereoscopic rendeing. Basically it
works by doing the drawing in QGraphicsView::paintEvent twice, once for
each buffer. This way the scene items are rendered to both buffers.
There's also an update to resolvement in QOpenGLWidgetPrivate
so that multisampling works correctly.

[ChangeLog][Widgets][QGraphicsView] Added support for
stereoscopic rendering.

Task-number: QTBUG-64587
Change-Id: I20650682daa805b64fe7f0d2ba086917d3f12229
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

8 files changed, 537 insertions, 0 deletions

diff --git a/tests/manual/stereographicsview/CMakeLists.txt b/tests/manual/stereographicsview/CMakeLists.txt
new file mode 100644
index 0000000000..937e10de91
--- /dev/null
+++ b/tests/manual/stereographicsview/CMakeLists.txt
@@ -0,0 +1,32 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+# Generated from stereographicsview.pro.
+
+#####################################################################
+## stereographicsview Binary:
+#####################################################################
+
+set(CMAKE_AUTOUIC ON)
+
+qt_internal_add_manual_test(stereographicsview
+    GUI
+    SOURCES
+        main.cpp
+        mainwindow.cpp
+        mainwindow.h
+        mainwindow.ui
+        mygraphicsview.h
+        mygraphicsview.cpp
+    LIBRARIES
+        Qt::CorePrivate
+        Qt::Gui
+        Qt::GuiPrivate
+        Qt::OpenGL
+        Qt::OpenGLWidgets
+        Qt::Widgets
+        Qt::WidgetsPrivate
+)
+
+#### Keys ignored in scope 1:.:.:stereographicsview.pro:<TRUE>:
+# TEMPLATE = "app"
diff --git a/tests/manual/stereographicsview/main.cpp b/tests/manual/stereographicsview/main.cpp
new file mode 100644
index 0000000000..6564e8efc4
--- /dev/null
+++ b/tests/manual/stereographicsview/main.cpp
@@ -0,0 +1,26 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "mainwindow.h"
+
+#include <QApplication>
+#include <QSurfaceFormat>
+
+int main(int argc, char *argv[])
+{
+    QApplication a(argc, argv);
+
+    QSurfaceFormat format;
+    format.setDepthBufferSize(24);
+    format.setStencilBufferSize(8);
+    format.setSamples(16);
+    format.setStereo(true);
+    QSurfaceFormat::setDefaultFormat(format);
+
+    MainWindow w;
+    w.show();
+    return a.exec();
+}
+
+
+#include "main.moc"
diff --git a/tests/manual/stereographicsview/mainwindow.cpp b/tests/manual/stereographicsview/mainwindow.cpp
new file mode 100644
index 0000000000..003b4da8c3
--- /dev/null
+++ b/tests/manual/stereographicsview/mainwindow.cpp
@@ -0,0 +1,79 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "mainwindow.h"
+#include "./ui_mainwindow.h"
+#include <QPushButton>
+#include <QSlider>
+#include <QLabel>
+#include <QGraphicsEllipseItem>
+#include <QRandomGenerator>
+#include <QOpenGLWidget>
+
+MainWindow::MainWindow(QWidget *parent)
+    : QMainWindow(parent)
+    , ui(new Ui::MainWindow)
+{
+    ui->setupUi(this);
+
+    ui->graphicsView->setViewport(new QOpenGLWidget);
+    ui->graphicsView->setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
+
+    QRect rect = ui->graphicsView->rect();
+    QGraphicsScene *m_scene = new QGraphicsScene(rect);
+    ui->graphicsView->setScene(m_scene);
+
+    QSize initialSize(150, 150);
+    m_ellipse = m_scene->addEllipse(
+        rect.width() / 2 - initialSize.width() / 2,
+        rect.height() / 2 - initialSize.height() / 2,
+        initialSize.width(),
+        initialSize.height(),
+        QPen(Qt::magenta, 5),
+        Qt::blue);
+
+    QPushButton *button = new QPushButton();
+    button->setGeometry(QRect(rect.width() / 2 - 75, 100, 150, 50));
+    button->setText("Random ellipse color");
+    QObject::connect(button, &QPushButton::pressed, [&]() {
+        m_ellipse->setBrush(QColor::fromRgb(QRandomGenerator::global()->generate()));
+        m_ellipse->setPen(QPen(QColor::fromRgb(QRandomGenerator::global()->generate()), 5));
+    });
+    m_scene->addWidget(button);
+
+    m_label = new QLabel();
+    m_label->setGeometry(QRect(rect.width() / 2 - 50, rect.height() - 100, 100, 50));
+    m_label->setAlignment(Qt::AlignCenter);
+    m_scene->addWidget(m_label);
+
+    QSlider *slider = new QSlider(Qt::Horizontal);
+    slider->setGeometry(QRect(rect.width() / 2 - 100, rect.height() - 50, 200, 50));
+    slider->setMinimum(10);
+    slider->setMaximum(300);
+    slider->setValue(initialSize.width());
+    QObject::connect(slider, &QAbstractSlider::valueChanged, [this](int value){
+        QRectF rect = m_ellipse->rect();
+        rect.setWidth(value);
+        rect.setHeight(value);
+        m_ellipse->setRect(rect);
+        m_label->setText("Ellipse size: " + QString::number(value));
+    });
+    emit slider->valueChanged(initialSize.width());
+    m_scene->addWidget(slider);
+
+    QMenu *screenShotMenu = menuBar()->addMenu("&Screenshot");
+    screenShotMenu->addAction("Left buffer", this, [this](){
+        ui->graphicsView->saveImage(QOpenGLWidget::LeftBuffer);
+    });
+
+    screenShotMenu->addAction("Right buffer", this, [this](){
+        ui->graphicsView->saveImage(QOpenGLWidget::RightBuffer);
+    });
+
+}
+
+MainWindow::~MainWindow()
+{
+    delete ui;
+}
+
diff --git a/tests/manual/stereographicsview/mainwindow.h b/tests/manual/stereographicsview/mainwindow.h
new file mode 100644
index 0000000000..4a65dad68d
--- /dev/null
+++ b/tests/manual/stereographicsview/mainwindow.h
@@ -0,0 +1,30 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef MAINWINDOW_H
+#define MAINWINDOW_H
+
+#include <QMainWindow>
+
+QT_BEGIN_NAMESPACE
+namespace Ui { class MainWindow; }
+QT_END_NAMESPACE
+
+class QGraphicsEllipseItem;
+class QLabel;
+
+class MainWindow : public QMainWindow
+{
+    Q_OBJECT
+
+public:
+    MainWindow(QWidget *parent = nullptr);
+    ~MainWindow();
+
+private:
+    QGraphicsEllipseItem *m_ellipse;
+    QLabel *m_label;
+
+    Ui::MainWindow *ui;
+};
+#endif // MAINWINDOW_H
diff --git a/tests/manual/stereographicsview/mainwindow.ui b/tests/manual/stereographicsview/mainwindow.ui
new file mode 100644
index 0000000000..2ebb6b8caa
--- /dev/null
+++ b/tests/manual/stereographicsview/mainwindow.ui
@@ -0,0 +1,101 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>MainWindow</class>
+ <widget class="QMainWindow" name="MainWindow">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>1120</width>
+    <height>695</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string>MainWindow</string>
+  </property>
+  <widget class="QWidget" name="centralwidget">
+   <layout class="QHBoxLayout" name="horizontalLayout">
+    <item>
+     <widget class="MyGraphicsView" name="graphicsView">
+      <property name="sizePolicy">
+       <sizepolicy hsizetype="MinimumExpanding" vsizetype="MinimumExpanding">
+        <horstretch>0</horstretch>
+        <verstretch>0</verstretch>
+       </sizepolicy>
+      </property>
+      <property name="minimumSize">
+       <size>
+        <width>0</width>
+        <height>0</height>
+       </size>
+      </property>
+      <property name="sizeAdjustPolicy">
+       <enum>QAbstractScrollArea::AdjustToContentsOnFirstShow</enum>
+      </property>
+     </widget>
+    </item>
+    <item>
+     <widget class="QFrame" name="frame">
+      <property name="sizePolicy">
+       <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
+        <horstretch>0</horstretch>
+        <verstretch>0</verstretch>
+       </sizepolicy>
+      </property>
+      <property name="frameShape">
+       <enum>QFrame::StyledPanel</enum>
+      </property>
+      <property name="frameShadow">
+       <enum>QFrame::Raised</enum>
+      </property>
+      <layout class="QVBoxLayout" name="verticalLayout">
+       <item>
+        <widget class="QLabel" name="label">
+         <property name="text">
+          <string>QGraphicsView Stereoscopic Example</string>
+         </property>
+         <property name="alignment">
+          <set>Qt::AlignCenter</set>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <spacer name="verticalSpacer">
+         <property name="orientation">
+          <enum>Qt::Vertical</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>20</width>
+           <height>40</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+      </layout>
+     </widget>
+    </item>
+   </layout>
+  </widget>
+  <widget class="QMenuBar" name="menubar">
+   <property name="geometry">
+    <rect>
+     <x>0</x>
+     <y>0</y>
+     <width>1120</width>
+     <height>21</height>
+    </rect>
+   </property>
+  </widget>
+  <widget class="QStatusBar" name="statusbar"/>
+ </widget>
+ <customwidgets>
+  <customwidget>
+   <class>MyGraphicsView</class>
+   <extends>QGraphicsView</extends>
+   <header>mygraphicsview.h</header>
+  </customwidget>
+ </customwidgets>
+ <resources/>
+ <connections/>
+</ui>
diff --git a/tests/manual/stereographicsview/mygraphicsview.cpp b/tests/manual/stereographicsview/mygraphicsview.cpp
new file mode 100644
index 0000000000..dc6e39f4a0
--- /dev/null
+++ b/tests/manual/stereographicsview/mygraphicsview.cpp
@@ -0,0 +1,209 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "mygraphicsview.h"
+#include <QResizeEvent>
+#include <QFileDialog>
+
+Q_OPENGL_EXPORT QImage qt_gl_read_framebuffer(const QSize &size, bool alpha_format, bool include_alpha);
+
+MyGraphicsView::MyGraphicsView(QWidget *parent) :
+    QGraphicsView(parent),
+    m_indexBuf(QOpenGLBuffer::IndexBuffer)
+{
+
+}
+
+MyGraphicsView::MyGraphicsView(QGraphicsScene *scene, QWidget *parent) :
+    QGraphicsView(scene, parent)
+{
+
+}
+
+void MyGraphicsView::saveImage(QOpenGLWidget::TargetBuffer targetBuffer)
+{
+    QOpenGLWidget *w = static_cast<QOpenGLWidget*>(viewport());
+    Q_ASSERT(w);
+
+    w->makeCurrent(targetBuffer);
+    draw(targetBuffer);
+
+    QImage img = qt_gl_read_framebuffer(w->size() * w->devicePixelRatio(), true, true);
+
+    if (img.isNull()) {
+        qFatal("Failed to grab framebuffer");
+    }
+
+    const char *fn =
+            targetBuffer == QOpenGLWidget::LeftBuffer
+            ? "leftBuffer.png" : "rightBuffer.png";
+
+    QFileDialog fd(this);
+    fd.setAcceptMode(QFileDialog::AcceptSave);
+    fd.setDefaultSuffix("png");
+    fd.selectFile(fn);
+    if (fd.exec() == QDialog::Accepted)
+        img.save(fd.selectedFiles().first());
+}
+
+void MyGraphicsView::drawBackground(QPainter *painter, const QRectF &rect)
+{
+    if (!m_initialized)
+        init();
+
+    QOpenGLWidget *w = static_cast<QOpenGLWidget*>(viewport());
+
+    painter->beginNativePainting();
+
+    draw(w->currentTargetBuffer());
+
+    painter->endNativePainting();
+
+
+    m_yaw += 0.5;
+    if (m_yaw > 360)
+        m_yaw = 0;
+}
+
+void MyGraphicsView::resizeEvent(QResizeEvent *event)
+{
+    QGraphicsView::resizeEvent(event);
+
+    resize(event->size().width(), event->size().height());
+}
+
+void MyGraphicsView::init()
+{
+    if (m_initialized)
+        return;
+
+    initializeOpenGLFunctions();
+
+    initShaders();
+    initCube();
+
+    resize(viewport()->width(), viewport()->height());
+
+    m_initialized = true;
+}
+
+void MyGraphicsView::initShaders()
+{
+    static const char *vertexShaderSource =
+            "#ifdef GL_ES\n"
+            "// Set default precision to medium\n"
+            "precision mediump int;\n"
+            "precision mediump float;\n"
+            "#endif\n"
+            "attribute vec4 a_position;\n"
+            "uniform mat4 u_mvp;\n"
+            "void main() {\n"
+               "gl_Position = u_mvp * a_position;\n"
+            "}\n";
+
+    static const char *fragmentShaderSource =
+            "#ifdef GL_ES\n"
+            "// Set default precision to medium\n"
+            "precision mediump int;\n"
+            "precision mediump float;\n"
+            "#endif\n"
+            "void main() {\n"
+               "gl_FragColor = vec4(0.7, 0.1, 0.0, 1.0);\n"
+            "}\n";
+
+    if (!m_program.addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource))
+        close();
+
+    if (!m_program.addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource))
+        close();
+
+    if (!m_program.link())
+        close();
+
+    if (!m_program.bind())
+        close();
+}
+
+void MyGraphicsView::initCube()
+{
+    m_arrayBuf.create();
+    m_indexBuf.create();
+
+    QVector3D vertices[] = {
+        QVector3D(-1.0f, -1.0f,  1.0f),
+        QVector3D( 1.0f, -1.0f,  1.0f),
+        QVector3D(-1.0f,  1.0f,  1.0f),
+        QVector3D( 1.0f,  1.0f,  1.0f),
+        QVector3D( 1.0f, -1.0f,  1.0f),
+        QVector3D( 1.0f, -1.0f, -1.0f),
+        QVector3D( 1.0f,  1.0f,  1.0f),
+        QVector3D( 1.0f,  1.0f, -1.0f),
+        QVector3D( 1.0f, -1.0f, -1.0f),
+        QVector3D(-1.0f, -1.0f, -1.0f),
+        QVector3D( 1.0f,  1.0f, -1.0f),
+        QVector3D(-1.0f,  1.0f, -1.0f),
+        QVector3D(-1.0f, -1.0f, -1.0f),
+        QVector3D(-1.0f, -1.0f,  1.0f),
+        QVector3D(-1.0f,  1.0f, -1.0f),
+        QVector3D(-1.0f,  1.0f,  1.0f),
+        QVector3D(-1.0f, -1.0f, -1.0f),
+        QVector3D( 1.0f, -1.0f, -1.0f),
+        QVector3D(-1.0f, -1.0f,  1.0f),
+        QVector3D( 1.0f, -1.0f,  1.0f),
+        QVector3D(-1.0f,  1.0f,  1.0f),
+        QVector3D( 1.0f,  1.0f,  1.0f),
+        QVector3D(-1.0f,  1.0f, -1.0f),
+        QVector3D( 1.0f,  1.0f, -1.0f)
+    };
+
+    GLushort indices[] = {
+        0,  1,  2,  3,  3,
+        4,  4,  5,  6,  7,  7,
+        8,  8,  9, 10, 11, 11,
+        12, 12, 13, 14, 15, 15,
+        16, 16, 17, 18, 19, 19,
+        20, 20, 21, 22, 23
+    };
+
+
+    m_arrayBuf.bind();
+    m_arrayBuf.allocate(vertices, 24 * sizeof(QVector3D));
+
+    m_indexBuf.bind();
+    m_indexBuf.allocate(indices, 34 * sizeof(GLushort));
+}
+
+void MyGraphicsView::draw(QOpenGLWidget::TargetBuffer targetBuffer)
+{
+    glClearColor(0.0f, 0.7f, 0.0f, 1.0f);
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+    m_program.bind();
+    m_arrayBuf.bind();
+    m_indexBuf.bind();
+
+    QMatrix4x4 matrix;
+    matrix.translate(targetBuffer == QOpenGLWidget::LeftBuffer ? -2.0 : 2.0,
+                     0.0,
+                     -10.0);
+    matrix.scale(2.0);
+    matrix.rotate(QQuaternion::fromEulerAngles(10, m_yaw, 0));
+    m_program.setUniformValue("u_mvp", m_projection * matrix);
+
+    int vertexLocation = m_program.attributeLocation("a_position");
+    m_program.enableAttributeArray(vertexLocation);
+    m_program.setAttributeBuffer(vertexLocation, GL_FLOAT, 0, 3, sizeof(QVector3D));
+
+    glDrawElements(GL_TRIANGLE_STRIP, 34, GL_UNSIGNED_SHORT, nullptr);
+}
+
+void MyGraphicsView::resize(int w, int h)
+{
+    qreal aspect = qreal(w) / qreal(h ? h : 1);
+    const qreal zNear = 0.0, zFar = 100.0, fov = 45.0;
+    m_projection.setToIdentity();
+    m_projection.perspective(fov, aspect, zNear, zFar);
+
+    if (m_initialized)
+        glViewport(0, 0, w, h);
+}
diff --git a/tests/manual/stereographicsview/mygraphicsview.h b/tests/manual/stereographicsview/mygraphicsview.h
new file mode 100644
index 0000000000..03204cb316
--- /dev/null
+++ b/tests/manual/stereographicsview/mygraphicsview.h
@@ -0,0 +1,47 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef MYGRAPHICSVIEW_H
+#define MYGRAPHICSVIEW_H
+
+#include <QOpenGLFunctions>
+#include <QGraphicsView>
+#include <QOpenGLShaderProgram>
+#include <QOpenGLBuffer>
+#include <QMatrix4x4>
+#include <QOpenGLWidget>
+
+class MyGraphicsView : public QGraphicsView, protected QOpenGLFunctions
+{
+public:
+    MyGraphicsView(QWidget *parent = nullptr);
+    MyGraphicsView(QGraphicsScene *scene, QWidget *parent = nullptr);
+
+    void saveImage(QOpenGLWidget::TargetBuffer targetBuffer);
+
+protected:
+    void drawBackground(QPainter *painter, const QRectF &rect) override;
+
+    void resizeEvent(QResizeEvent *event) override;
+
+private:
+    void init();
+    void initShaders();
+    void initCube();
+
+    void draw(QOpenGLWidget::TargetBuffer targetBuffer);
+
+    void resize(int w, int h);
+
+
+    bool m_initialized = false;
+
+    QOpenGLShaderProgram m_program;
+    QMatrix4x4 m_projection;
+    QOpenGLBuffer m_arrayBuf;
+    QOpenGLBuffer m_indexBuf;
+
+    qreal m_yaw = 0;
+};
+
+#endif // MYGRAPHICSVIEW_H
diff --git a/tests/manual/stereographicsview/stereographicsview.pro b/tests/manual/stereographicsview/stereographicsview.pro
new file mode 100644
index 0000000000..597166367c
--- /dev/null
+++ b/tests/manual/stereographicsview/stereographicsview.pro
@@ -0,0 +1,13 @@
+QT += widgets widgets-private gui-private core-private
+
+TARGET = stereographicsview
+TEMPLATE = app
+
+SOURCES += main.cpp \
+        mainwindow.cpp \
+        mainwindow.h \
+        mainwindow.ui \
+        mygraphicsview.h \
+        mygraphicsview.cpp \
+
+HEADERS  += openglwidget.h