Clean up and modernize hellominimalcrossgfxtriangle manual test

This particular test may serve as sample code in various materials in
the future, therefore it is highly beneficial if it is kept in good shape.

Make it easier to read, more compact, and split up among the natural
boundaries of the functionality (global setup in main, window+swapchain
management in Window, graphics resource setup and draw call recording
in HelloWindow).

Change-Id: I2451d3961a01131dcbffe66baf23d2cf9bfd077f
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

7 files changed, 782 insertions, 552 deletions

diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.cpp b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.cpp
deleted file mode 100644
index 9b03a48bfe..0000000000
--- a/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.cpp
+++ /dev/null
@@ -1,550 +0,0 @@
-/****************************************************************************
-**
-** Copyright (C) 2018 The Qt Company Ltd.
-** Contact: https://www.qt.io/licensing/
-**
-** This file is part of the examples of the Qt Toolkit.
-**
-** $QT_BEGIN_LICENSE:BSD$
-** Commercial License Usage
-** Licensees holding valid commercial Qt licenses may use this file in
-** accordance with the commercial license agreement provided with the
-** Software or, alternatively, in accordance with the terms contained in
-** a written agreement between you and The Qt Company. For licensing terms
-** and conditions see https://www.qt.io/terms-conditions. For further
-** information use the contact form at https://www.qt.io/contact-us.
-**
-** BSD License Usage
-** Alternatively, you may use this file under the terms of the BSD license
-** as follows:
-**
-** "Redistribution and use in source and binary forms, with or without
-** modification, are permitted provided that the following conditions are
-** met:
-**   * Redistributions of source code must retain the above copyright
-**     notice, this list of conditions and the following disclaimer.
-**   * Redistributions in binary form must reproduce the above copyright
-**     notice, this list of conditions and the following disclaimer in
-**     the documentation and/or other materials provided with the
-**     distribution.
-**   * Neither the name of The Qt Company Ltd nor the names of its
-**     contributors may be used to endorse or promote products derived
-**     from this software without specific prior written permission.
-**
-**
-** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
-**
-** $QT_END_LICENSE$
-**
-****************************************************************************/
-
-// This is a compact, minimal, single-file demo of deciding the backend at
-// runtime while using the exact same shaders and rendering code without any
-// branching whatsoever once the QWindow is up and the RHI is initialized.
-
-#include <QGuiApplication>
-#include <QCommandLineParser>
-#include <QWindow>
-#include <QPlatformSurfaceEvent>
-#include <QElapsedTimer>
-
-#include <QtGui/private/qshader_p.h>
-#include <QFile>
-
-#include <QtGui/private/qrhinull_p.h>
-
-#ifndef QT_NO_OPENGL
-#include <QtGui/private/qrhigles2_p.h>
-#include <QOffscreenSurface>
-#endif
-
-#if QT_CONFIG(vulkan)
-#include <QLoggingCategory>
-#include <QtGui/private/qrhivulkan_p.h>
-#endif
-
-#ifdef Q_OS_WIN
-#include <QtGui/private/qrhid3d11_p.h>
-#endif
-
-#if defined(Q_OS_MACOS) || defined(Q_OS_IOS)
-#include <QtGui/private/qrhimetal_p.h>
-#endif
-
-static float vertexData[] = {
-    // Y up (note clipSpaceCorrMatrix in m_proj), CCW
-     0.0f,   0.5f,   1.0f, 0.0f, 0.0f,
-    -0.5f,  -0.5f,   0.0f, 1.0f, 0.0f,
-     0.5f,  -0.5f,   0.0f, 0.0f, 1.0f,
-};
-
-static QShader getShader(const QString &name)
-{
-    QFile f(name);
-    if (f.open(QIODevice::ReadOnly))
-        return QShader::fromSerialized(f.readAll());
-
-    return QShader();
-}
-
-enum GraphicsApi
-{
-    OpenGL,
-    Vulkan,
-    D3D11,
-    Metal,
-    Null
-};
-
-static GraphicsApi graphicsApi;
-
-static QString graphicsApiName()
-{
-    switch (graphicsApi) {
-    case OpenGL:
-        return QLatin1String("OpenGL 2.x");
-    case Vulkan:
-        return QLatin1String("Vulkan");
-    case D3D11:
-        return QLatin1String("Direct3D 11");
-    case Metal:
-        return QLatin1String("Metal");
-    case Null:
-        return QLatin1String("Null");
-    default:
-        break;
-    }
-    return QString();
-}
-
-class Window : public QWindow
-{
-public:
-    Window();
-    ~Window();
-
-    void init();
-    void releaseResources();
-    void resizeSwapChain();
-    void releaseSwapChain();
-    void render();
-
-    void exposeEvent(QExposeEvent *) override;
-    bool event(QEvent *) override;
-
-private:
-    bool m_running = false;
-    bool m_notExposed = false;
-    bool m_newlyExposed = false;
-
-    QRhi *m_r = nullptr;
-    bool m_hasSwapChain = false;
-    QRhiSwapChain *m_sc = nullptr;
-    QRhiRenderBuffer *m_ds = nullptr;
-    QRhiRenderPassDescriptor *m_rp = nullptr;
-    QRhiBuffer *m_vbuf = nullptr;
-    bool m_vbufReady = false;
-    QRhiBuffer *m_ubuf = nullptr;
-    QRhiShaderResourceBindings *m_srb = nullptr;
-    QRhiGraphicsPipeline *m_ps = nullptr;
-    QVector<QRhiResource *> releasePool;
-
-    QMatrix4x4 m_proj;
-    float m_rotation = 0;
-    float m_opacity = 1;
-    int m_opacityDir = -1;
-
-    QElapsedTimer m_timer;
-    qint64 m_elapsedMs;
-    int m_elapsedCount;
-
-#ifndef QT_NO_OPENGL
-    QOffscreenSurface *m_fallbackSurface = nullptr;
-#endif
-};
-
-Window::Window()
-{
-    // Tell the platform plugin what we want.
-    switch (graphicsApi) {
-    case OpenGL:
-#if QT_CONFIG(opengl)
-        setSurfaceType(OpenGLSurface);
-        setFormat(QRhiGles2InitParams::adjustedFormat());
-#endif
-        break;
-    case Vulkan:
-        setSurfaceType(VulkanSurface);
-        break;
-    case D3D11:
-        setSurfaceType(OpenGLSurface); // not a typo
-        break;
-    case Metal:
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 12, 0))
-        setSurfaceType(MetalSurface);
-#endif
-        break;
-    default:
-        break;
-    }
-}
-
-Window::~Window()
-{
-    releaseResources();
-}
-
-void Window::exposeEvent(QExposeEvent *)
-{
-    // initialize and start rendering when the window becomes usable for graphics purposes
-    if (isExposed() && !m_running) {
-        m_running = true;
-        init();
-        resizeSwapChain();
-    }
-
-    // stop pushing frames when not exposed (or size is 0)
-    if ((!isExposed() || (m_hasSwapChain && m_sc->surfacePixelSize().isEmpty())) && m_running)
-        m_notExposed = true;
-
-    // continue when exposed again and the surface has a valid size.
-    // note that the surface size can be (0, 0) even though size() reports a valid one...
-    if (isExposed() && m_running && m_notExposed && !m_sc->surfacePixelSize().isEmpty()) {
-        m_notExposed = false;
-        m_newlyExposed = true;
-    }
-
-    // always render a frame on exposeEvent() (when exposed) in order to update
-    // immediately on window resize.
-    if (isExposed() && !m_sc->surfacePixelSize().isEmpty())
-        render();
-}
-
-bool Window::event(QEvent *e)
-{
-    switch (e->type()) {
-    case QEvent::UpdateRequest:
-        render();
-        break;
-
-    case QEvent::PlatformSurface:
-        // this is the proper time to tear down the swapchain (while the native window and surface are still around)
-        if (static_cast<QPlatformSurfaceEvent *>(e)->surfaceEventType() == QPlatformSurfaceEvent::SurfaceAboutToBeDestroyed)
-            releaseSwapChain();
-        break;
-
-    default:
-        break;
-    }
-
-    return QWindow::event(e);
-}
-
-void Window::init()
-{
-    if (graphicsApi == Null) {
-        QRhiNullInitParams params;
-        m_r = QRhi::create(QRhi::Null, &params);
-    }
-
-#ifndef QT_NO_OPENGL
-    if (graphicsApi == OpenGL) {
-        m_fallbackSurface = QRhiGles2InitParams::newFallbackSurface();
-        QRhiGles2InitParams params;
-        params.fallbackSurface = m_fallbackSurface;
-        params.window = this;
-        m_r = QRhi::create(QRhi::OpenGLES2, &params);
-    }
-#endif
-
-#if QT_CONFIG(vulkan)
-    if (graphicsApi == Vulkan) {
-        QRhiVulkanInitParams params;
-        params.inst = vulkanInstance();
-        params.window = this;
-        m_r = QRhi::create(QRhi::Vulkan, &params);
-    }
-#endif
-
-#ifdef Q_OS_WIN
-    if (graphicsApi == D3D11) {
-        QRhiD3D11InitParams params;
-        m_r = QRhi::create(QRhi::D3D11, &params);
-    }
-#endif
-
-#if defined(Q_OS_MACOS) || defined(Q_OS_IOS)
-    if (graphicsApi == Metal) {
-        QRhiMetalInitParams params;
-        m_r = QRhi::create(QRhi::Metal, &params);
-    }
-#endif
-
-    if (!m_r)
-        qFatal("Failed to create RHI backend");
-
-    // now onto the backend-independent init
-
-    m_sc = m_r->newSwapChain();
-    // allow depth-stencil, although we do not actually enable depth test/write for the triangle
-    m_ds = m_r->newRenderBuffer(QRhiRenderBuffer::DepthStencil,
-                                QSize(), // no need to set the size here, due to UsedWithSwapChainOnly
-                                1,
-                                QRhiRenderBuffer::UsedWithSwapChainOnly);
-    releasePool << m_ds;
-    m_sc->setWindow(this);
-    m_sc->setDepthStencil(m_ds);
-    m_rp = m_sc->newCompatibleRenderPassDescriptor();
-    releasePool << m_rp;
-    m_sc->setRenderPassDescriptor(m_rp);
-
-    m_vbuf = m_r->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(vertexData));
-    releasePool << m_vbuf;
-    m_vbuf->build();
-    m_vbufReady = false;
-
-    m_ubuf = m_r->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 68);
-    releasePool << m_ubuf;
-    m_ubuf->build();
-
-    m_srb = m_r->newShaderResourceBindings();
-    releasePool << m_srb;
-    m_srb->setBindings({
-        QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage, m_ubuf)
-    });
-    m_srb->build();
-
-    m_ps = m_r->newGraphicsPipeline();
-    releasePool << m_ps;
-
-    QRhiGraphicsPipeline::TargetBlend premulAlphaBlend;
-    premulAlphaBlend.enable = true;
-    m_ps->setTargetBlends({ premulAlphaBlend });
-
-    const QShader vs = getShader(QLatin1String(":/color.vert.qsb"));
-    if (!vs.isValid())
-        qFatal("Failed to load shader pack (vertex)");
-    const QShader fs = getShader(QLatin1String(":/color.frag.qsb"));
-    if (!fs.isValid())
-        qFatal("Failed to load shader pack (fragment)");
-
-    m_ps->setShaderStages({
-        { QRhiShaderStage::Vertex, vs },
-        { QRhiShaderStage::Fragment, fs }
-    });
-
-    QRhiVertexInputLayout inputLayout;
-    inputLayout.setBindings({
-        { 5 * sizeof(float) }
-    });
-    inputLayout.setAttributes({
-        { 0, 0, QRhiVertexInputAttribute::Float2, 0 },
-        { 0, 1, QRhiVertexInputAttribute::Float3, 2 * sizeof(float) }
-    });
-
-    m_ps->setVertexInputLayout(inputLayout);
-    m_ps->setShaderResourceBindings(m_srb);
-    m_ps->setRenderPassDescriptor(m_rp);
-
-    m_ps->build();
-}
-
-void Window::releaseResources()
-{
-    qDeleteAll(releasePool);
-    releasePool.clear();
-
-    delete m_sc; // native swapchain is likely released already
-    m_sc = nullptr;
-
-    delete m_r;
-
-#ifndef QT_NO_OPENGL
-    delete m_fallbackSurface;
-#endif
-}
-
-void Window::resizeSwapChain()
-{
-    m_hasSwapChain = m_sc->buildOrResize(); // also handles m_ds
-
-    m_elapsedMs = 0;
-    m_elapsedCount = 0;
-
-    const QSize outputSize = m_sc->currentPixelSize();
-    m_proj = m_r->clipSpaceCorrMatrix();
-    m_proj.perspective(45.0f, outputSize.width() / (float) outputSize.height(), 0.01f, 100.0f);
-    m_proj.translate(0, 0, -4);
-}
-
-void Window::releaseSwapChain()
-{
-    if (m_hasSwapChain) {
-        m_hasSwapChain = false;
-        m_sc->release();
-    }
-}
-
-void Window::render()
-{
-    if (!m_hasSwapChain || m_notExposed)
-        return;
-
-    // If the window got resized or got newly exposed, resize the swapchain.
-    // (the newly-exposed case is not actually required by some
-    // platforms/backends, but f.ex. Vulkan on Windows seems to need it)
-    if (m_sc->currentPixelSize() != m_sc->surfacePixelSize() || m_newlyExposed) {
-        resizeSwapChain();
-        if (!m_hasSwapChain)
-            return;
-        m_newlyExposed = false;
-    }
-
-    // Start a new frame. This is where we block when too far ahead of
-    // GPU/present, and that's what throttles the thread to the refresh rate.
-    // (except for OpenGL where it happens either in endFrame or somewhere else
-    // depending on the GL implementation)
-    QRhi::FrameOpResult r = m_r->beginFrame(m_sc);
-    if (r == QRhi::FrameOpSwapChainOutOfDate) {
-        resizeSwapChain();
-        if (!m_hasSwapChain)
-            return;
-        r = m_r->beginFrame(m_sc);
-    }
-    if (r != QRhi::FrameOpSuccess) {
-        requestUpdate();
-        return;
-    }
-
-    if (m_elapsedCount)
-        m_elapsedMs += m_timer.elapsed();
-    m_timer.restart();
-    m_elapsedCount += 1;
-    if (m_elapsedMs >= 4000) {
-        qDebug("%f", m_elapsedCount / 4.0f);
-        m_elapsedMs = 0;
-        m_elapsedCount = 0;
-    }
-
-    // Set up buffer updates.
-    QRhiResourceUpdateBatch *u = m_r->nextResourceUpdateBatch();
-    if (!m_vbufReady) {
-        m_vbufReady = true;
-        u->uploadStaticBuffer(m_vbuf, vertexData);
-    }
-    m_rotation += 1.0f;
-    QMatrix4x4 mvp = m_proj;
-    mvp.rotate(m_rotation, 0, 1, 0);
-    u->updateDynamicBuffer(m_ubuf, 0, 64, mvp.constData());
-    m_opacity += m_opacityDir * 0.005f;
-    if (m_opacity < 0.0f || m_opacity > 1.0f) {
-        m_opacityDir *= -1;
-        m_opacity = qBound(0.0f, m_opacity, 1.0f);
-    }
-    u->updateDynamicBuffer(m_ubuf, 64, 4, &m_opacity);
-
-    QRhiCommandBuffer *cb = m_sc->currentFrameCommandBuffer();
-    const QSize outputSizeInPixels = m_sc->currentPixelSize();
-
-    // Apply buffer updates, clear, start the renderpass (where applicable).
-    cb->beginPass(m_sc->currentFrameRenderTarget(), QColor::fromRgbF(0.4f, 0.7f, 0.0f, 1.0f), { 1.0f, 0 }, u);
-
-    cb->setGraphicsPipeline(m_ps);
-    cb->setViewport({ 0, 0, float(outputSizeInPixels.width()), float(outputSizeInPixels.height()) });
-    cb->setShaderResources();
-
-    const QRhiCommandBuffer::VertexInput vbufBinding(m_vbuf, 0);
-    cb->setVertexInput(0, 1, &vbufBinding);
-    cb->draw(3);
-
-    cb->endPass();
-
-    // Submit.
-    m_r->endFrame(m_sc);
-
-    requestUpdate(); // render continuously, throttled by the presentation rate (due to beginFrame above)
-}
-
-int main(int argc, char **argv)
-{
-    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
-    QGuiApplication app(argc, argv);
-
-    // Defaults.
-#if defined(Q_OS_WIN)
-    graphicsApi = D3D11;
-#elif defined(Q_OS_MACOS) || defined(Q_OS_IOS)
-    graphicsApi = Metal;
-#elif QT_CONFIG(vulkan)
-    graphicsApi = Vulkan;
-#else
-    graphicsApi = OpenGL;
-#endif
-
-    // Allow overriding via the command line.
-    QCommandLineParser cmdLineParser;
-    cmdLineParser.addHelpOption();
-    QCommandLineOption glOption({ "g", "opengl" }, QLatin1String("OpenGL (2.x)"));
-    cmdLineParser.addOption(glOption);
-    QCommandLineOption vkOption({ "v", "vulkan" }, QLatin1String("Vulkan"));
-    cmdLineParser.addOption(vkOption);
-    QCommandLineOption d3dOption({ "d", "d3d11" }, QLatin1String("Direct3D 11"));
-    cmdLineParser.addOption(d3dOption);
-    QCommandLineOption mtlOption({ "m", "metal" }, QLatin1String("Metal"));
-    cmdLineParser.addOption(mtlOption);
-    QCommandLineOption nullOption({ "n", "null" }, QLatin1String("Null"));
-    cmdLineParser.addOption(nullOption);
-    cmdLineParser.process(app);
-    if (cmdLineParser.isSet(glOption))
-        graphicsApi = OpenGL;
-    if (cmdLineParser.isSet(vkOption))
-        graphicsApi = Vulkan;
-    if (cmdLineParser.isSet(d3dOption))
-        graphicsApi = D3D11;
-    if (cmdLineParser.isSet(mtlOption))
-        graphicsApi = Metal;
-    if (cmdLineParser.isSet(nullOption))
-        graphicsApi = Null;
-
-    // Vulkan setup.
-#if QT_CONFIG(vulkan)
-    QVulkanInstance inst;
-    if (graphicsApi == Vulkan) {
-        if (!inst.create()) {
-            qWarning("Failed to create Vulkan instance, switching to OpenGL");
-            graphicsApi = OpenGL;
-        }
-    }
-#endif
-
-    // Create and show the window.
-    Window w;
-#if QT_CONFIG(vulkan)
-    if (graphicsApi == Vulkan)
-        w.setVulkanInstance(&inst);
-#endif
-    w.resize(1280, 720);
-    w.setTitle(graphicsApiName());
-    w.show();
-
-    // Window::event() will not get invoked when the
-    // PlatformSurfaceAboutToBeDestroyed event is sent during the QWindow
-    // destruction. That happens only when exiting via app::quit() instead of
-    // the more common QWindow::close(). Take care of it: if the
-    // QPlatformWindow is still around (there was no close() yet), get rid of
-    // the swapchain while it's not too late.
-    if (w.handle())
-        w.releaseSwapChain();
-
-    return app.exec();
-}
diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.pro b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.pro
index eeef33ff6a..a1093fdaec 100644
--- a/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.pro
+++ b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellominimalcrossgfxtriangle.pro
@@ -1,8 +1,14 @@
 TEMPLATE = app
-
+CONFIG += console
 QT += gui-private
 
 SOURCES = \
-    hellominimalcrossgfxtriangle.cpp
+    main.cpp \
+    window.cpp \
+    hellowindow.cpp
+
+HEADERS = \
+    window.h \
+    hellowindow.h
 
 RESOURCES = hellominimalcrossgfxtriangle.qrc
diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/hellowindow.cpp b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellowindow.cpp
new file mode 100644
index 0000000000..96a088adf4
--- /dev/null
+++ b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellowindow.cpp
@@ -0,0 +1,159 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "hellowindow.h"
+#include <QFile>
+#include <QtGui/private/qshader_p.h>
+
+static float vertexData[] = {
+    // Y up (note clipSpaceCorrMatrix in m_proj), CCW
+     0.0f,   0.5f,   1.0f, 0.0f, 0.0f,
+    -0.5f,  -0.5f,   0.0f, 1.0f, 0.0f,
+     0.5f,  -0.5f,   0.0f, 0.0f, 1.0f,
+};
+
+HelloWindow::HelloWindow(QRhi::Implementation graphicsApi)
+    : Window(graphicsApi)
+{
+}
+
+QShader HelloWindow::getShader(const QString &name)
+{
+    QFile f(name);
+    if (f.open(QIODevice::ReadOnly))
+        return QShader::fromSerialized(f.readAll());
+
+    return QShader();
+}
+
+void HelloWindow::customInit()
+{
+    m_vbuf.reset(m_rhi->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(vertexData)));
+    m_vbuf->build();
+    m_vbufReady = false;
+
+    m_ubuf.reset(m_rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 68));
+    m_ubuf->build();
+
+    m_srb.reset(m_rhi->newShaderResourceBindings());
+    m_srb->setBindings({
+            QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage,
+                                                     m_ubuf.get())
+    });
+    m_srb->build();
+
+    m_ps.reset(m_rhi->newGraphicsPipeline());
+
+    QRhiGraphicsPipeline::TargetBlend premulAlphaBlend;
+    premulAlphaBlend.enable = true;
+    m_ps->setTargetBlends({ premulAlphaBlend });
+
+    const QShader vs = getShader(QLatin1String(":/color.vert.qsb"));
+    if (!vs.isValid())
+        qFatal("Failed to load shader pack (vertex)");
+    const QShader fs = getShader(QLatin1String(":/color.frag.qsb"));
+    if (!fs.isValid())
+        qFatal("Failed to load shader pack (fragment)");
+
+    m_ps->setShaderStages({
+        { QRhiShaderStage::Vertex, vs },
+        { QRhiShaderStage::Fragment, fs }
+    });
+
+    QRhiVertexInputLayout inputLayout;
+    inputLayout.setBindings({
+        { 5 * sizeof(float) }
+    });
+    inputLayout.setAttributes({
+        { 0, 0, QRhiVertexInputAttribute::Float2, 0 },
+        { 0, 1, QRhiVertexInputAttribute::Float3, 2 * sizeof(float) }
+    });
+
+    m_ps->setVertexInputLayout(inputLayout);
+    m_ps->setShaderResourceBindings(m_srb.get());
+    m_ps->setRenderPassDescriptor(m_rp.get());
+
+    m_ps->build();
+}
+
+// called once per frame
+void HelloWindow::customRender()
+{
+    QRhiResourceUpdateBatch *u = m_rhi->nextResourceUpdateBatch();
+    if (!m_vbufReady) {
+        m_vbufReady = true;
+        u->uploadStaticBuffer(m_vbuf.get(), vertexData);
+    }
+    m_rotation += 1.0f;
+    QMatrix4x4 mvp = m_proj;
+    mvp.rotate(m_rotation, 0, 1, 0);
+    u->updateDynamicBuffer(m_ubuf.get(), 0, 64, mvp.constData());
+    m_opacity += m_opacityDir * 0.005f;
+    if (m_opacity < 0.0f || m_opacity > 1.0f) {
+        m_opacityDir *= -1;
+        m_opacity = qBound(0.0f, m_opacity, 1.0f);
+    }
+    u->updateDynamicBuffer(m_ubuf.get(), 64, 4, &m_opacity);
+
+    QRhiCommandBuffer *cb = m_sc->currentFrameCommandBuffer();
+    const QSize outputSizeInPixels = m_sc->currentPixelSize();
+
+    cb->beginPass(m_sc->currentFrameRenderTarget(), QColor::fromRgbF(0.4f, 0.7f, 0.0f, 1.0f), { 1.0f, 0 }, u);
+
+    cb->setGraphicsPipeline(m_ps.get());
+    cb->setViewport({ 0, 0, float(outputSizeInPixels.width()), float(outputSizeInPixels.height()) });
+    cb->setShaderResources();
+
+    const QRhiCommandBuffer::VertexInput vbufBinding(m_vbuf.get(), 0);
+    cb->setVertexInput(0, 1, &vbufBinding);
+    cb->draw(3);
+
+    cb->endPass();
+}
diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/hellowindow.h b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellowindow.h
new file mode 100644
index 0000000000..dd9890f11c
--- /dev/null
+++ b/tests/manual/rhi/hellominimalcrossgfxtriangle/hellowindow.h
@@ -0,0 +1,78 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef HELLOWINDOW_H
+#define HELLOWINDOW_H
+
+#include "window.h"
+
+class HelloWindow : public Window
+{
+public:
+    HelloWindow(QRhi::Implementation graphicsApi);
+
+    void customInit() override;
+    void customRender() override;
+
+private:
+    QShader getShader(const QString &name);
+
+    std::unique_ptr<QRhiBuffer> m_vbuf;
+    bool m_vbufReady = false;
+    std::unique_ptr<QRhiBuffer> m_ubuf;
+    std::unique_ptr<QRhiShaderResourceBindings> m_srb;
+    std::unique_ptr<QRhiGraphicsPipeline> m_ps;
+
+    float m_rotation = 0;
+    float m_opacity = 1;
+    int m_opacityDir = -1;
+};
+
+#endif
diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/main.cpp b/tests/manual/rhi/hellominimalcrossgfxtriangle/main.cpp
new file mode 100644
index 0000000000..4ef3359ed0
--- /dev/null
+++ b/tests/manual/rhi/hellominimalcrossgfxtriangle/main.cpp
@@ -0,0 +1,171 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+// This is a compact, minimal demo of deciding the backend at runtime while
+// using the exact same shaders and rendering code without any branching
+// whatsoever once the QWindow is up and the RHI is initialized.
+
+#include <QGuiApplication>
+#include <QCommandLineParser>
+#include "hellowindow.h"
+
+QString graphicsApiName(QRhi::Implementation graphicsApi)
+{
+    switch (graphicsApi) {
+    case QRhi::Null:
+        return QLatin1String("Null (no output)");
+    case QRhi::OpenGLES2:
+        return QLatin1String("OpenGL 2.x");
+    case QRhi::Vulkan:
+        return QLatin1String("Vulkan");
+    case QRhi::D3D11:
+        return QLatin1String("Direct3D 11");
+    case QRhi::Metal:
+        return QLatin1String("Metal");
+    default:
+        break;
+    }
+    return QString();
+}
+
+int main(int argc, char **argv)
+{
+    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QGuiApplication app(argc, argv);
+
+    QRhi::Implementation graphicsApi;
+#if defined(Q_OS_WIN)
+    graphicsApi = QRhi::D3D11;
+#elif defined(Q_OS_MACOS) || defined(Q_OS_IOS)
+    graphicsApi = QRhi::Metal;
+#elif QT_CONFIG(vulkan)
+    graphicsApi = QRhi::Vulkan;
+#else
+    graphicsApi = QRhi::OpenGLES2;
+#endif
+
+    QCommandLineParser cmdLineParser;
+    cmdLineParser.addHelpOption();
+    QCommandLineOption nullOption({ "n", "null" }, QLatin1String("Null"));
+    cmdLineParser.addOption(nullOption);
+    QCommandLineOption glOption({ "g", "opengl" }, QLatin1String("OpenGL (2.x)"));
+    cmdLineParser.addOption(glOption);
+    QCommandLineOption vkOption({ "v", "vulkan" }, QLatin1String("Vulkan"));
+    cmdLineParser.addOption(vkOption);
+    QCommandLineOption d3dOption({ "d", "d3d11" }, QLatin1String("Direct3D 11"));
+    cmdLineParser.addOption(d3dOption);
+    QCommandLineOption mtlOption({ "m", "metal" }, QLatin1String("Metal"));
+    cmdLineParser.addOption(mtlOption);
+
+    cmdLineParser.process(app);
+    if (cmdLineParser.isSet(nullOption))
+        graphicsApi = QRhi::Null;
+    if (cmdLineParser.isSet(glOption))
+        graphicsApi = QRhi::OpenGLES2;
+    if (cmdLineParser.isSet(vkOption))
+        graphicsApi = QRhi::Vulkan;
+    if (cmdLineParser.isSet(d3dOption))
+        graphicsApi = QRhi::D3D11;
+    if (cmdLineParser.isSet(mtlOption))
+        graphicsApi = QRhi::Metal;
+
+    qDebug("Selected graphics API is %s", qPrintable(graphicsApiName(graphicsApi)));
+    qDebug("This is a multi-api example, use command line arguments to override:\n%s", qPrintable(cmdLineParser.helpText()));
+
+    QSurfaceFormat fmt;
+    fmt.setDepthBufferSize(24);
+    fmt.setStencilBufferSize(8);
+    QSurfaceFormat::setDefaultFormat(fmt);
+
+#if QT_CONFIG(vulkan)
+    QVulkanInstance inst;
+    if (graphicsApi == QRhi::Vulkan) {
+#ifndef Q_OS_ANDROID
+        inst.setLayers({ "VK_LAYER_LUNARG_standard_validation" });
+#else
+        inst.setLayers({
+                "VK_LAYER_GOOGLE_threading",
+                "VK_LAYER_LUNARG_parameter_validation",
+                "VK_LAYER_LUNARG_object_tracker",
+                "VK_LAYER_LUNARG_core_validation",
+                "VK_LAYER_LUNARG_image",
+                "VK_LAYER_LUNARG_swapchain",
+                "VK_LAYER_GOOGLE_unique_objects"});
+#endif
+        inst.setExtensions({ "VK_KHR_get_physical_device_properties2" });
+        if (!inst.create()) {
+            qWarning("Failed to create Vulkan instance, switching to OpenGL");
+            graphicsApi = QRhi::OpenGLES2;
+        }
+    }
+#endif
+
+    HelloWindow w(graphicsApi);
+#if QT_CONFIG(vulkan)
+    if (graphicsApi == QRhi::Vulkan)
+        w.setVulkanInstance(&inst);
+#endif
+    w.resize(1280, 720);
+    w.setTitle(QCoreApplication::applicationName() + QLatin1String(" - ") + graphicsApiName(graphicsApi));
+    w.show();
+
+    int ret = app.exec();
+
+    // Window::event() will not get invoked when the
+    // PlatformSurfaceAboutToBeDestroyed event is sent during the QWindow
+    // destruction. That happens only when exiting via app::quit() instead of
+    // the more common QWindow::close(). Take care of it: if the QPlatformWindow
+    // is still around (there was no close() yet), get rid of the swapchain
+    // while it's not too late.
+    if (w.handle())
+        w.releaseSwapChain();
+
+    return ret;
+}
diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/window.cpp b/tests/manual/rhi/hellominimalcrossgfxtriangle/window.cpp
new file mode 100644
index 0000000000..f3f00e0255
--- /dev/null
+++ b/tests/manual/rhi/hellominimalcrossgfxtriangle/window.cpp
@@ -0,0 +1,255 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "window.h"
+#include <QPlatformSurfaceEvent>
+
+Window::Window(QRhi::Implementation graphicsApi)
+    : m_graphicsApi(graphicsApi)
+{
+    switch (graphicsApi) {
+    case QRhi::OpenGLES2:
+        setSurfaceType(OpenGLSurface);
+#if QT_CONFIG(opengl)
+        setFormat(QRhiGles2InitParams::adjustedFormat());
+#endif
+        break;
+    case QRhi::Vulkan:
+        setSurfaceType(VulkanSurface);
+        break;
+    case QRhi::D3D11:
+        setSurfaceType(OpenGLSurface);
+        break;
+    case QRhi::Metal:
+        setSurfaceType(MetalSurface);
+        break;
+    default:
+        break;
+    }
+}
+
+void Window::exposeEvent(QExposeEvent *)
+{
+    // initialize and start rendering when the window becomes usable for graphics purposes
+    if (isExposed() && !m_running) {
+        qDebug("init");
+        m_running = true;
+        init();
+        resizeSwapChain();
+    }
+
+    const QSize surfaceSize = m_hasSwapChain ? m_sc->surfacePixelSize() : QSize();
+
+    // stop pushing frames when not exposed (or size is 0)
+    if ((!isExposed() || (m_hasSwapChain && surfaceSize.isEmpty())) && m_running && !m_notExposed) {
+        qDebug("not exposed");
+        m_notExposed = true;
+    }
+
+    // Continue when exposed again and the surface has a valid size. Note that
+    // surfaceSize can be (0, 0) even though size() reports a valid one, hence
+    // trusting surfacePixelSize() and not QWindow.
+    if (isExposed() && m_running && m_notExposed && !surfaceSize.isEmpty()) {
+        qDebug("exposed again");
+        m_notExposed = false;
+        m_newlyExposed = true;
+    }
+
+    // always render a frame on exposeEvent() (when exposed) in order to update
+    // immediately on window resize.
+    if (isExposed() && !surfaceSize.isEmpty())
+        render();
+}
+
+bool Window::event(QEvent *e)
+{
+    switch (e->type()) {
+    case QEvent::UpdateRequest:
+        render();
+        break;
+
+    case QEvent::PlatformSurface:
+        // this is the proper time to tear down the swapchain (while the native window and surface are still around)
+        if (static_cast<QPlatformSurfaceEvent *>(e)->surfaceEventType() == QPlatformSurfaceEvent::SurfaceAboutToBeDestroyed)
+            releaseSwapChain();
+        break;
+
+    default:
+        break;
+    }
+
+    return QWindow::event(e);
+}
+
+void Window::init()
+{
+    QRhi::Flags rhiFlags = QRhi::EnableDebugMarkers | QRhi::EnableProfiling;
+
+    if (m_graphicsApi == QRhi::Null) {
+        QRhiNullInitParams params;
+        m_rhi.reset(QRhi::create(QRhi::Null, &params, rhiFlags));
+    }
+
+#if QT_CONFIG(opengl)
+    if (m_graphicsApi == QRhi::OpenGLES2) {
+        m_fallbackSurface.reset(QRhiGles2InitParams::newFallbackSurface());
+        QRhiGles2InitParams params;
+        params.fallbackSurface = m_fallbackSurface.get();
+        params.window = this;
+        m_rhi.reset(QRhi::create(QRhi::OpenGLES2, &params, rhiFlags));
+    }
+#endif
+
+#if QT_CONFIG(vulkan)
+    if (m_graphicsApi == QRhi::Vulkan) {
+        QRhiVulkanInitParams params;
+        params.inst = vulkanInstance();
+        params.window = this;
+        m_rhi.reset(QRhi::create(QRhi::Vulkan, &params, rhiFlags));
+    }
+#endif
+
+#ifdef Q_OS_WIN
+    if (m_graphicsApi == QRhi::D3D11) {
+        QRhiD3D11InitParams params;
+        params.enableDebugLayer = true;
+        m_rhi.reset(QRhi::create(QRhi::D3D11, &params, rhiFlags));
+    }
+#endif
+
+#if defined(Q_OS_MACOS) || defined(Q_OS_IOS)
+    if (m_graphicsApi == QRhi::Metal) {
+        QRhiMetalInitParams params;
+        m_rhi = QRhi::create(QRhi::Metal, &params, rhiFlags);
+    }
+#endif
+
+    if (!m_rhi)
+        qFatal("Failed to create RHI backend");
+
+    m_sc.reset(m_rhi->newSwapChain());
+    m_ds.reset(m_rhi->newRenderBuffer(QRhiRenderBuffer::DepthStencil,
+                                      QSize(), // no need to set the size here, due to UsedWithSwapChainOnly
+                                      1,
+                                      QRhiRenderBuffer::UsedWithSwapChainOnly));
+    m_sc->setWindow(this);
+    m_sc->setDepthStencil(m_ds.get());
+    m_rp.reset(m_sc->newCompatibleRenderPassDescriptor());
+    m_sc->setRenderPassDescriptor(m_rp.get());
+
+    customInit();
+}
+
+void Window::resizeSwapChain()
+{
+    m_hasSwapChain = m_sc->buildOrResize(); // also handles m_ds
+
+    const QSize outputSize = m_sc->currentPixelSize();
+    m_proj = m_rhi->clipSpaceCorrMatrix();
+    m_proj.perspective(45.0f, outputSize.width() / (float) outputSize.height(), 0.01f, 1000.0f);
+    m_proj.translate(0, 0, -4);
+}
+
+void Window::releaseSwapChain()
+{
+    if (m_hasSwapChain) {
+        m_hasSwapChain = false;
+        m_sc->release();
+    }
+}
+
+void Window::render()
+{
+    if (!m_hasSwapChain || m_notExposed)
+        return;
+
+    // If the window got resized or newly exposed, resize the swapchain. (the
+    // newly-exposed case is not actually required by some platforms, but
+    // f.ex. Vulkan on Windows seems to need it)
+    //
+    // This (exposeEvent + the logic here) is the only safe way to perform
+    // resize handling. Note the usage of the RHI's surfacePixelSize(), and
+    // never QWindow::size(). (the two may or may not be the same under the hood,
+    // depending on the backend and platform)
+    //
+    if (m_sc->currentPixelSize() != m_sc->surfacePixelSize() || m_newlyExposed) {
+        resizeSwapChain();
+        if (!m_hasSwapChain)
+            return;
+        m_newlyExposed = false;
+    }
+
+    QRhi::FrameOpResult r = m_rhi->beginFrame(m_sc.get());
+    if (r == QRhi::FrameOpSwapChainOutOfDate) {
+        resizeSwapChain();
+        if (!m_hasSwapChain)
+            return;
+        r = m_rhi->beginFrame(m_sc.get());
+    }
+    if (r != QRhi::FrameOpSuccess) {
+        qDebug("beginFrame failed with %d, retry", r);
+        requestUpdate();
+        return;
+    }
+
+    customRender();
+
+    m_rhi->endFrame(m_sc.get());
+
+    requestUpdate();
+}
+
+void Window::customInit()
+{
+}
+
+void Window::customRender()
+{
+}
diff --git a/tests/manual/rhi/hellominimalcrossgfxtriangle/window.h b/tests/manual/rhi/hellominimalcrossgfxtriangle/window.h
new file mode 100644
index 0000000000..30bfa2492c
--- /dev/null
+++ b/tests/manual/rhi/hellominimalcrossgfxtriangle/window.h
@@ -0,0 +1,111 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef WINDOW_H
+#define WINDOW_H
+
+#include <QWindow>
+
+#include <QtGui/private/qrhinull_p.h>
+#if QT_CONFIG(opengl)
+#include <QtGui/private/qrhigles2_p.h>
+#include <QOffscreenSurface>
+#endif
+#if QT_CONFIG(vulkan)
+#include <QtGui/private/qrhivulkan_p.h>
+#endif
+#ifdef Q_OS_WIN
+#include <QtGui/private/qrhid3d11_p.h>
+#endif
+#if defined(Q_OS_MACOS) || defined(Q_OS_IOS)
+#include <QtGui/private/qrhimetal_p.h>
+#endif
+
+class Window : public QWindow
+{
+public:
+    Window(QRhi::Implementation graphicsApi);
+
+    void releaseSwapChain();
+
+protected:
+    virtual void customInit();
+    virtual void customRender();
+
+    // destruction order matters to a certain degree: the fallbackSurface must
+    // outlive the rhi, the rhi must outlive all other resources.  The resources
+    // need no special order when destroying.
+#if QT_CONFIG(opengl)
+    std::unique_ptr<QOffscreenSurface> m_fallbackSurface;
+#endif
+    std::unique_ptr<QRhi> m_rhi;
+    std::unique_ptr<QRhiSwapChain> m_sc;
+    std::unique_ptr<QRhiRenderBuffer> m_ds;
+    std::unique_ptr<QRhiRenderPassDescriptor> m_rp;
+
+    bool m_hasSwapChain = false;
+    QMatrix4x4 m_proj;
+
+private:
+    void init();
+    void resizeSwapChain();
+    void render();
+
+    void exposeEvent(QExposeEvent *) override;
+    bool event(QEvent *) override;
+
+    QRhi::Implementation m_graphicsApi;
+
+    bool m_running = false;
+    bool m_notExposed = false;
+    bool m_newlyExposed = false;
+};
+
+#endif