Add support for stereoscopic content in QRhi::OpenGLES2

Setting the flag QSurfaceFormat::StereoBuffers does not actually do
anything, because we do not utilize the extra buffers provided. We need
to expose setting the correct buffers using glDrawBuffers between draw
calls.

Change-Id: I6a5110405e621030ac3a2886fa83df0cfe928723
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/gui/rhi/qrhi.cpp

@@ -4859,6 +4859,35 @@ QRhiResource::Type QRhiSwapChain::resourceType() const
     \note the value must not be cached and reused between frames
  */
 
+/*!
+    \enum QRhiSwapChain::StereoTargetBuffer
+    Selects the backbuffer to use with a stereoscopic swapchain.
+
+    \value LeftBuffer
+    \value RightBuffer
+ */
+
+/*!
+    \return a render target that can be used with beginPass() in order to
+    render to the swapchain's left or right backbuffer. This overload should be
+    used only with stereoscopic rendering, that is, when the associated QWindow
+    is backed by two color buffers, one for each eye, instead of just one.
+
+    When stereoscopic rendering is not supported, the return value will be
+    null. For the time being the only backend and 3D API where traditional
+    stereoscopic rendering is supported is OpenGL (excluding OpenGL ES), in
+    combination with \l QSurfaceFormat::StereoBuffers, assuming it is supported
+    by the graphics and display driver stack at run time. All other backends
+    are going to return null from this overload.
+
+    \note the value must not be cached and reused between frames
+ */
+QRhiRenderTarget *QRhiSwapChain::currentFrameRenderTarget(StereoTargetBuffer targetBuffer)
+{
+    Q_UNUSED(targetBuffer);
+    return nullptr;
+}
+
 /*!
     \fn bool QRhiSwapChain::createOrResize()
 

src/gui/rhi/qrhi_p.h

@@ -1379,6 +1379,11 @@ public:
         HDR10
     };
 
+    enum StereoTargetBuffer {
+        LeftBuffer,
+        RightBuffer
+    };
+
     QRhiResource::Type resourceType() const override;
 
     QWindow *window() const { return m_window; }
@@ -1403,6 +1408,7 @@ public:
 
     virtual QRhiCommandBuffer *currentFrameCommandBuffer() = 0;
     virtual QRhiRenderTarget *currentFrameRenderTarget() = 0;
+    virtual QRhiRenderTarget *currentFrameRenderTarget(StereoTargetBuffer targetBuffer);
     virtual QSize surfacePixelSize() = 0;
     virtual bool isFormatSupported(Format f) = 0;
     virtual QRhiRenderPassDescriptor *newCompatibleRenderPassDescriptor() = 0;

src/gui/rhi/qrhigles2.cpp

@@ -435,6 +435,14 @@ QT_BEGIN_NAMESPACE
 #define GL_GEOMETRY_SHADER                0x8DD9
 #endif
 
+#ifndef GL_BACK_LEFT
+#define GL_BACK_LEFT                      0x0402
+#endif
+
+#ifndef GL_BACK_RIGHT
+#define GL_BACK_RIGHT                     0x0403
+#endif
+
 /*!
     Constructs a new QRhiGles2InitParams.
 
@@ -2997,24 +3005,31 @@ void QRhiGles2::executeCommandBuffer(QRhiCommandBuffer *cb)
                                 cmd.args.bindShaderResources.dynamicOffsetCount);
             break;
         case QGles2CommandBuffer::Command::BindFramebuffer:
+        {
+            QVarLengthArray<GLenum, 8> bufs;
             if (cmd.args.bindFramebuffer.fbo) {
                 f->glBindFramebuffer(GL_FRAMEBUFFER, cmd.args.bindFramebuffer.fbo);
+                const int colorAttCount = cmd.args.bindFramebuffer.colorAttCount;
+                bufs.append(colorAttCount > 0 ? GL_COLOR_ATTACHMENT0 : GL_NONE);
                 if (caps.maxDrawBuffers > 1) {
-                    const int colorAttCount = cmd.args.bindFramebuffer.colorAttCount;
+                    for (int i = 1; i < colorAttCount; ++i)
-                    QVarLengthArray<GLenum, 8> bufs;
-                    for (int i = 0; i < colorAttCount; ++i)
                         bufs.append(GL_COLOR_ATTACHMENT0 + uint(i));
-                    f->glDrawBuffers(colorAttCount, bufs.constData());
                 }
             } else {
                 f->glBindFramebuffer(GL_FRAMEBUFFER, ctx->defaultFramebufferObject());
+                if (cmd.args.bindFramebuffer.stereo && cmd.args.bindFramebuffer.stereoTarget == QRhiSwapChain::RightBuffer)
+                    bufs.append(GL_BACK_RIGHT);
+                else
+                    bufs.append(caps.gles ? GL_BACK : GL_BACK_LEFT);
             }
+            f->glDrawBuffers(bufs.count(), bufs.constData());
             if (caps.srgbCapableDefaultFramebuffer) {
                 if (cmd.args.bindFramebuffer.srgb)
                     f->glEnable(GL_FRAMEBUFFER_SRGB);
                 else
                     f->glDisable(GL_FRAMEBUFFER_SRGB);
             }
+        }
             break;
         case QGles2CommandBuffer::Command::Clear:
             f->glDisable(GL_SCISSOR_TEST);
@@ -3980,6 +3995,9 @@ QGles2RenderTargetData *QRhiGles2::enqueueBindFramebuffer(QRhiRenderTarget *rt,
             *wantsDsClear = doClearBuffers;
         fbCmd.args.bindFramebuffer.fbo = 0;
         fbCmd.args.bindFramebuffer.colorAttCount = 1;
+        fbCmd.args.bindFramebuffer.stereo = rtD->stereoTarget.has_value();
+        if (fbCmd.args.bindFramebuffer.stereo)
+            fbCmd.args.bindFramebuffer.stereoTarget = rtD->stereoTarget.value();
         break;
     case QRhiResource::TextureRenderTarget:
     {
@@ -3991,6 +4009,7 @@ QGles2RenderTargetData *QRhiGles2::enqueueBindFramebuffer(QRhiRenderTarget *rt,
             *wantsDsClear = !rtTex->m_flags.testFlag(QRhiTextureRenderTarget::PreserveDepthStencilContents);
         fbCmd.args.bindFramebuffer.fbo = rtTex->framebuffer;
         fbCmd.args.bindFramebuffer.colorAttCount = rtD->colorAttCount;
+        fbCmd.args.bindFramebuffer.stereo = false;
 
         for (auto it = rtTex->m_desc.cbeginColorAttachments(), itEnd = rtTex->m_desc.cendColorAttachments();
              it != itEnd; ++it)
@@ -5753,6 +5772,8 @@ void QGles2CommandBuffer::destroy()
 QGles2SwapChain::QGles2SwapChain(QRhiImplementation *rhi)
     : QRhiSwapChain(rhi),
       rt(rhi, this),
+      rtLeft(rhi, this),
+      rtRight(rhi, this),
       cb(rhi)
 {
 }
@@ -5779,6 +5800,16 @@ QRhiRenderTarget *QGles2SwapChain::currentFrameRenderTarget()
     return &rt;
 }
 
+QRhiRenderTarget *QGles2SwapChain::currentFrameRenderTarget(StereoTargetBuffer targetBuffer)
+{
+    if (targetBuffer == LeftBuffer)
+        return rtLeft.d.isValid() ? &rtLeft : &rt;
+    else if (targetBuffer == RightBuffer)
+        return rtRight.d.isValid() ? &rtRight : &rt;
+    else
+        Q_UNREACHABLE_RETURN(nullptr);
+}
+
 QSize QGles2SwapChain::surfacePixelSize()
 {
     Q_ASSERT(m_window);
@@ -5795,6 +5826,18 @@ QRhiRenderPassDescriptor *QGles2SwapChain::newCompatibleRenderPassDescriptor()
     return new QGles2RenderPassDescriptor(m_rhi);
 }
 
+void QGles2SwapChain::initSwapChainRenderTarget(QGles2SwapChainRenderTarget *rt)
+{
+    rt->setRenderPassDescriptor(m_renderPassDesc); // for the public getter in QRhiRenderTarget
+    rt->d.rp = QRHI_RES(QGles2RenderPassDescriptor, m_renderPassDesc);
+    rt->d.pixelSize = pixelSize;
+    rt->d.dpr = float(m_window->devicePixelRatio());
+    rt->d.sampleCount = qBound(1, m_sampleCount, 64);
+    rt->d.colorAttCount = 1;
+    rt->d.dsAttCount = m_depthStencil ? 1 : 0;
+    rt->d.srgbUpdateAndBlend = m_flags.testFlag(QRhiSwapChain::sRGB);
+}
+
 bool QGles2SwapChain::createOrResize()
 {
     // can be called multiple times due to window resizes
@@ -5813,14 +5856,14 @@ bool QGles2SwapChain::createOrResize()
         m_depthStencil->create();
     }
 
-    rt.setRenderPassDescriptor(m_renderPassDesc); // for the public getter in QRhiRenderTarget
+    initSwapChainRenderTarget(&rt);
-    rt.d.rp = QRHI_RES(QGles2RenderPassDescriptor, m_renderPassDesc);
+
-    rt.d.pixelSize = pixelSize;
+    if (m_window->format().stereo()) {
-    rt.d.dpr = float(m_window->devicePixelRatio());
+        initSwapChainRenderTarget(&rtLeft);
-    rt.d.sampleCount = qBound(1, m_sampleCount, 64);
+        rtLeft.d.stereoTarget = QRhiSwapChain::LeftBuffer;
-    rt.d.colorAttCount = 1;
+        initSwapChainRenderTarget(&rtRight);
-    rt.d.dsAttCount = m_depthStencil ? 1 : 0;
+        rtRight.d.stereoTarget = QRhiSwapChain::RightBuffer;
-    rt.d.srgbUpdateAndBlend = m_flags.testFlag(QRhiSwapChain::sRGB);
+    }
 
     frameCount = 0;
 

src/gui/rhi/qrhigles2_p_p.h

@@ -23,6 +23,7 @@
 #include <QWindow>
 #include <QPointer>
 #include <QtCore/private/qduplicatetracker_p.h>
+#include <optional>
 
 QT_BEGIN_NAMESPACE
 
@@ -173,6 +174,8 @@ struct QGles2RenderTargetData
 {
     QGles2RenderTargetData(QRhiImplementation *) { }
 
+    bool isValid() const { return rp != nullptr; }
+
     QGles2RenderPassDescriptor *rp = nullptr;
     QSize pixelSize;
     float dpr = 1;
@@ -181,6 +184,7 @@ struct QGles2RenderTargetData
     int dsAttCount = 0;
     bool srgbUpdateAndBlend = false;
     QRhiRenderTargetAttachmentTracker::ResIdList currentResIdList;
+    std::optional<QRhiSwapChain::StereoTargetBuffer> stereoTarget;
 };
 
 struct QGles2SwapChainRenderTarget : public QRhiSwapChainRenderTarget
@@ -399,6 +403,8 @@ struct QGles2CommandBuffer : public QRhiCommandBuffer
                 GLuint fbo;
                 bool srgb;
                 int colorAttCount;
+                bool stereo;
+                QRhiSwapChain::StereoTargetBuffer stereoTarget;
             } bindFramebuffer;
             struct {
                 GLenum target;
@@ -690,6 +696,7 @@ struct QGles2SwapChain : public QRhiSwapChain
 
     QRhiCommandBuffer *currentFrameCommandBuffer() override;
     QRhiRenderTarget *currentFrameRenderTarget() override;
+    QRhiRenderTarget *currentFrameRenderTarget(StereoTargetBuffer targetBuffer) override;
 
     QSize surfacePixelSize() override;
     bool isFormatSupported(Format f) override;
@@ -697,9 +704,13 @@ struct QGles2SwapChain : public QRhiSwapChain
     QRhiRenderPassDescriptor *newCompatibleRenderPassDescriptor() override;
     bool createOrResize() override;
 
+    void initSwapChainRenderTarget(QGles2SwapChainRenderTarget *rt);
+
     QSurface *surface = nullptr;
     QSize pixelSize;
     QGles2SwapChainRenderTarget rt;
+    QGles2SwapChainRenderTarget rtLeft;
+    QGles2SwapChainRenderTarget rtRight;
     QGles2CommandBuffer cb;
     int frameCount = 0;
 };

tests/manual/rhi/CMakeLists.txt

@@ -30,6 +30,7 @@ add_subdirectory(polygonmode)
 add_subdirectory(tessellation)
 add_subdirectory(geometryshader)
 add_subdirectory(stenciloutline)
+add_subdirectory(stereo)
 if(QT_FEATURE_widgets)
     add_subdirectory(rhiwidget)
 endif()

tests/manual/rhi/stereo/CMakeLists.txt

@@ -0,0 +1,40 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+# Generated from stereo.pro.
+
+#####################################################################
+## stereo Binary:
+#####################################################################
+
+qt_internal_add_manual_test(stereo
+    SOURCES
+        main.cpp
+        window.cpp window.h
+    LIBRARIES
+        Qt::Gui
+        Qt::GuiPrivate
+)
+
+# Resources:
+set_source_files_properties("../shared/color.frag.qsb"
+    PROPERTIES QT_RESOURCE_ALIAS "color.frag.qsb"
+)
+set_source_files_properties("../shared/color.vert.qsb"
+    PROPERTIES QT_RESOURCE_ALIAS "color.vert.qsb"
+)
+set(stereo_resource_files
+    "../shared/color.frag.qsb"
+    "../shared/color.vert.qsb"
+)
+
+qt_internal_add_resource(stereo "stereo"
+    PREFIX
+        "/"
+    FILES
+        ${stereo_resource_files}
+)
+
+
+#### Keys ignored in scope 1:.:.:stereo.pro:<TRUE>:
+# TEMPLATE = "app"

tests/manual/rhi/stereo/main.cpp

@@ -0,0 +1,36 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+// This is a demo showing stereoscopic rendering.
+// For now, the backend is hardcoded to be OpenGL, because that's the only
+// supported backend.
+
+#include <QGuiApplication>
+#include <QCommandLineParser>
+#include "window.h"
+
+int main(int argc, char **argv)
+{
+    QGuiApplication app(argc, argv);
+
+    QSurfaceFormat fmt;
+    fmt.setDepthBufferSize(24);
+    fmt.setStencilBufferSize(8);
+
+    // Request stereoscopic rendering support with left/right buffers
+    fmt.setStereo(true);
+
+    QSurfaceFormat::setDefaultFormat(fmt);
+
+    Window w;
+    w.resize(1280, 720);
+    w.setTitle(QCoreApplication::applicationName());
+    w.show();
+
+    int ret = app.exec();
+
+    if (w.handle())
+        w.releaseSwapChain();
+
+    return ret;
+}

tests/manual/rhi/stereo/stereo.pro

@@ -0,0 +1,12 @@
+TEMPLATE = app
+CONFIG += console
+QT += gui-private
+
+SOURCES = \
+    main.cpp \
+    window.cpp
+
+HEADERS = \
+    window.h
+
+RESOURCES = stereo.qrc

tests/manual/rhi/stereo/stereo.qrc

@@ -0,0 +1,6 @@
+<!DOCTYPE RCC><RCC version="1.0">
+<qresource>
+  <file alias="color.vert.qsb">../shared/color.vert.qsb</file>
+  <file alias="color.frag.qsb">../shared/color.frag.qsb</file>
+</qresource>
+</RCC>

tests/manual/rhi/stereo/window.cpp

@@ -0,0 +1,264 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "window.h"
+#include <QPlatformSurfaceEvent>
+#include <QTimer>
+#include <QFile>
+#include <QtGui/private/qshader_p.h>
+#include "../shared/cube.h"
+
+Window::Window()
+{
+    setSurfaceType(OpenGLSurface);
+}
+
+void Window::exposeEvent(QExposeEvent *)
+{
+    if (isExposed() && !m_running) {
+        m_running = true;
+        init();
+        resizeSwapChain();
+    }
+
+    const QSize surfaceSize = m_hasSwapChain ? m_sc->surfacePixelSize() : QSize();
+    if ((!isExposed() || (m_hasSwapChain && surfaceSize.isEmpty())) && m_running && !m_notExposed)
+        m_notExposed = true;
+
+    if (isExposed() && m_running && m_notExposed && !surfaceSize.isEmpty()) {
+        m_notExposed = false;
+        m_newlyExposed = true;
+    }
+
+    if (isExposed() && !surfaceSize.isEmpty())
+        render();
+}
+
+bool Window::event(QEvent *e)
+{
+    switch (e->type()) {
+    case QEvent::UpdateRequest:
+        render();
+        break;
+
+    case QEvent::PlatformSurface:
+        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;
+
+    m_fallbackSurface.reset(QRhiGles2InitParams::newFallbackSurface());
+    QRhiGles2InitParams params;
+    params.fallbackSurface = m_fallbackSurface.get();
+    params.window = this;
+    m_rhi.reset(QRhi::create(QRhi::OpenGLES2, &params, rhiFlags));
+
+    m_sc.reset(m_rhi->newSwapChain());
+    m_ds.reset(m_rhi->newRenderBuffer(QRhiRenderBuffer::DepthStencil,
+                                      QSize(),
+                                      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());
+
+    m_vbuf.reset(m_rhi->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(cube)));
+    m_vbuf->setName(QByteArrayLiteral("vbuf"));
+    m_vbuf->create();
+    m_vbufReady = false;
+
+    m_ubuf.reset(m_rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 64 + 4));
+    m_ubuf->setName(QByteArrayLiteral("Left eye"));
+    m_ubuf->create();
+
+    m_srb.reset(m_rhi->newShaderResourceBindings());
+    m_srb->setBindings({
+            QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage,
+                                                     m_ubuf.get())
+    });
+    m_srb->create();
+
+
+    m_ubuf2.reset(m_rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 64 + 4));
+    m_ubuf2->setName(QByteArrayLiteral("Right eye"));
+    m_ubuf2->create();
+
+    m_srb2.reset(m_rhi->newShaderResourceBindings());
+    m_srb2->setBindings({
+            QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage,
+                                                     m_ubuf2.get())
+    });
+    m_srb2->create();
+
+    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({
+            { 3 * sizeof(float) },
+            { 2 * sizeof(float) }
+    });
+    inputLayout.setAttributes({
+            { 0, 0, QRhiVertexInputAttribute::Float3, 0 },
+            { 1, 1, QRhiVertexInputAttribute::Float2, 0 }
+    });
+
+    m_ps->setVertexInputLayout(inputLayout);
+    m_ps->setShaderResourceBindings(m_srb.get());
+    m_ps->setRenderPassDescriptor(m_rp.get());
+
+    m_ps->create();
+
+    m_ps->setDepthTest(true);
+    m_ps->setDepthWrite(true);
+    m_ps->setDepthOp(QRhiGraphicsPipeline::Less);
+
+    m_ps->setCullMode(QRhiGraphicsPipeline::Back);
+    m_ps->setFrontFace(QRhiGraphicsPipeline::CCW);
+}
+
+void Window::resizeSwapChain()
+{
+    m_hasSwapChain = m_sc->createOrResize(); // 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->destroy();
+    }
+}
+
+void Window::render()
+{
+    if (!m_hasSwapChain || m_notExposed)
+        return;
+
+    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;
+    }
+
+    recordFrame();
+
+    m_rhi->endFrame(m_sc.get());
+
+    QTimer::singleShot(0, this, [this] { render(); });
+}
+
+QShader Window::getShader(const QString &name)
+{
+    QFile f(name);
+    if (f.open(QIODevice::ReadOnly))
+        return QShader::fromSerialized(f.readAll());
+
+    return QShader();
+}
+
+// called once per frame
+void Window::recordFrame()
+{
+    QRhiResourceUpdateBatch *u = m_rhi->nextResourceUpdateBatch();
+    if (!m_vbufReady) {
+        m_vbufReady = true;
+        u->uploadStaticBuffer(m_vbuf.get(), cube);
+    }
+
+    QRhiCommandBuffer *cb = m_sc->currentFrameCommandBuffer();
+    const QSize outputSizeInPixels = m_sc->currentPixelSize();
+
+    const QColor clearColor = QColor::fromRgbF(0.15f, 0.15f, 0.15f, 1.0f);
+    const QRhiDepthStencilClearValue depthStencil = { 1.0f, 0 };
+    const QRhiViewport viewPort = { 0, 0, float(outputSizeInPixels.width()), float(outputSizeInPixels.height()) };
+    const QRhiCommandBuffer::VertexInput vbufBindings[] = {
+        { m_vbuf.get(), 0 },
+        { m_vbuf.get(), quint32(36 * 3 * sizeof(float)) }
+    };
+
+    QMatrix4x4 mvp = m_rhi->clipSpaceCorrMatrix();
+    mvp.perspective(45.0f, outputSizeInPixels.width() / (float) outputSizeInPixels.height(), 0.01f, 100.0f);
+
+    m_translation += m_translationDir * 0.05f;
+    if (m_translation < -10.0f || m_translation > -5.0f) {
+        m_translationDir *= -1;
+        m_translation = qBound(-10.0f, m_translation, -5.0f);
+    }
+    mvp.translate(0, 0, m_translation);
+    m_rotation += .5f;
+    mvp.rotate(m_rotation, 0, 1, 0);
+    u->updateDynamicBuffer(m_ubuf.get(), 0, 64, mvp.constData());
+
+    float opacity = 1.0f;
+    u->updateDynamicBuffer(m_ubuf.get(), 64, 4, &opacity);
+
+    QMatrix4x4 mvp2 = mvp;
+    mvp2.translate(-2.f, 0, 0);
+
+    u->updateDynamicBuffer(m_ubuf2.get(), 0, 64, mvp2.constData());
+    u->updateDynamicBuffer(m_ubuf2.get(), 64, 4, &opacity);
+
+    cb->resourceUpdate(u);
+
+    cb->beginPass(m_sc->currentFrameRenderTarget(QRhiSwapChain::LeftBuffer), clearColor, depthStencil);
+    cb->setGraphicsPipeline(m_ps.get());
+    cb->setViewport(viewPort);
+    cb->setShaderResources(m_srb.get());
+    cb->setVertexInput(0, 2, vbufBindings);
+    cb->draw(36);
+    cb->endPass();
+
+    cb->beginPass(m_sc->currentFrameRenderTarget(QRhiSwapChain::RightBuffer), clearColor, depthStencil);
+    cb->setGraphicsPipeline(m_ps.get());
+    cb->setViewport(viewPort);
+    cb->setShaderResources(m_srb2.get());
+    cb->setVertexInput(0, 2, vbufBindings);
+    cb->draw(36);
+    cb->endPass();
+}

tests/manual/rhi/stereo/window.h

@@ -0,0 +1,56 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef WINDOW_H
+#define WINDOW_H
+
+#include <QWindow>
+#include <QtGui/private/qrhigles2_p.h>
+#include <QOffscreenSurface>
+
+class Window : public QWindow
+{
+public:
+    Window();
+
+    void releaseSwapChain();
+
+protected:
+    std::unique_ptr<QOffscreenSurface> m_fallbackSurface;
+    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 recordFrame();
+
+    void exposeEvent(QExposeEvent *) override;
+    bool event(QEvent *) override;
+
+    bool m_running = false;
+    bool m_notExposed = false;
+    bool m_newlyExposed = false;
+
+    QShader getShader(const QString &name);
+
+    std::unique_ptr<QRhiBuffer> m_vbuf;
+    bool m_vbufReady = false;
+    std::unique_ptr<QRhiBuffer> m_ubuf;
+    std::unique_ptr<QRhiBuffer> m_ubuf2;
+    std::unique_ptr<QRhiShaderResourceBindings> m_srb;
+    std::unique_ptr<QRhiShaderResourceBindings> m_srb2;
+    std::unique_ptr<QRhiGraphicsPipeline> m_ps;
+
+    float m_rotation = 0;
+    float m_translation = -5;
+    int m_translationDir = -1;
+};
+
+#endif