Move backing store OpenGL support to the platformcompositor module

QPlatformBackingStore had a dependency on the QOpenGLTextureBlitter, which is a
problem because we want to get rid of all the public QOpenGL* classes in the
gui module.

This splits the heavily QOpenGL dependent parts of the backing store
implementation into a separate class and moves it to the platformcompositor
module.

qplatformbackingstore.cpp is now mostly free from OpenGL implementation
details.

Platform integrations now have to explicitly request backing store OpenGL
support. This has been done for:

- xcb
- windows
- cocoa
- winrt
- android
- wasm
- ios

QPlatformGraphicsBufferHelper::lockAndBindToTexture is now exported so it can
be used from other modules.

Task-number: QTBUG-74409
Change-Id: I42ad9250e5a424939cf751a8ad880c7381ede2ae
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 31 insertions, 408 deletions

diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index c092a7153f..e8ac494e04 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -40,43 +40,8 @@
 #include "qplatformbackingstore.h"
 #include <qwindow.h>
 #include <qpixmap.h>
-#include <private/qwindow_p.h>
-
-#include <qopengl.h>
-#include <qopenglcontext.h>
-#include <QtGui/QMatrix4x4>
-#include <QtGui/QOpenGLShaderProgram>
-#include <QtGui/QOpenGLContext>
-#include <QtGui/QOpenGLFunctions>
-#ifndef QT_NO_OPENGL
-#include <QtGui/qopengltextureblitter.h>
-#include <QtGui/qoffscreensurface.h>
-#endif
-#include <qpa/qplatformgraphicsbuffer.h>
-#include <qpa/qplatformgraphicsbufferhelper.h>
 
-#ifndef GL_TEXTURE_BASE_LEVEL
-#define GL_TEXTURE_BASE_LEVEL             0x813C
-#endif
-#ifndef GL_TEXTURE_MAX_LEVEL
-#define GL_TEXTURE_MAX_LEVEL              0x813D
-#endif
-#ifndef GL_UNPACK_ROW_LENGTH
-#define GL_UNPACK_ROW_LENGTH              0x0CF2
-#endif
-#ifndef GL_RGB10_A2
-#define GL_RGB10_A2                       0x8059
-#endif
-#ifndef GL_UNSIGNED_INT_2_10_10_10_REV
-#define GL_UNSIGNED_INT_2_10_10_10_REV    0x8368
-#endif
-
-#ifndef GL_FRAMEBUFFER_SRGB
-#define GL_FRAMEBUFFER_SRGB 0x8DB9
-#endif
-#ifndef GL_FRAMEBUFFER_SRGB_CAPABLE
-#define GL_FRAMEBUFFER_SRGB_CAPABLE 0x8DBA
-#endif
+#include <QtCore/private/qobject_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -88,38 +53,19 @@ public:
     QPlatformBackingStorePrivate(QWindow *w)
         : window(w)
         , backingStore(nullptr)
-#ifndef QT_NO_OPENGL
-        , textureId(0)
-        , blitter(nullptr)
-#endif
     {
     }
 
     ~QPlatformBackingStorePrivate()
     {
 #ifndef QT_NO_OPENGL
-        if (context) {
-            QOffscreenSurface offscreenSurface;
-            offscreenSurface.setFormat(context->format());
-            offscreenSurface.create();
-            context->makeCurrent(&offscreenSurface);
-            if (textureId)
-                context->functions()->glDeleteTextures(1, &textureId);
-            if (blitter)
-                blitter->destroy();
-        }
-        delete blitter;
+        delete openGLSupport;
 #endif
     }
     QWindow *window;
     QBackingStore *backingStore;
 #ifndef QT_NO_OPENGL
-    QScopedPointer<QOpenGLContext> context;
-    mutable GLuint textureId;
-    mutable QSize textureSize;
-    mutable bool needsSwizzle;
-    mutable bool premultiplied;
-    QOpenGLTextureBlitter *blitter;
+    QPlatformBackingStoreOpenGLSupportBase *openGLSupport = nullptr;
 #endif
 };
 
@@ -240,83 +186,20 @@ void QPlatformTextureList::clear()
 */
 
 #ifndef QT_NO_OPENGL
-
-static inline QRect deviceRect(const QRect &rect, QWindow *window)
-{
-    QRect deviceRect(rect.topLeft() * window->devicePixelRatio(),
-                     rect.size() * window->devicePixelRatio());
-    return deviceRect;
-}
-
-static inline QPoint deviceOffset(const QPoint &pt, QWindow *window)
-{
-    return pt * window->devicePixelRatio();
-}
-
-static QRegion deviceRegion(const QRegion &region, QWindow *window, const QPoint &offset)
-{
-    if (offset.isNull() && window->devicePixelRatio() <= 1)
-        return region;
-
-    QVector<QRect> rects;
-    rects.reserve(region.rectCount());
-    for (const QRect &rect : region)
-        rects.append(deviceRect(rect.translated(offset), window));
-
-    QRegion deviceRegion;
-    deviceRegion.setRects(rects.constData(), rects.count());
-    return deviceRegion;
-}
-
-static inline QRect toBottomLeftRect(const QRect &topLeftRect, int windowHeight)
-{
-    return QRect(topLeftRect.x(), windowHeight - topLeftRect.bottomRight().y() - 1,
-                 topLeftRect.width(), topLeftRect.height());
-}
-
-static void blitTextureForWidget(const QPlatformTextureList *textures, int idx, QWindow *window, const QRect &deviceWindowRect,
-                                 QOpenGLTextureBlitter *blitter, const QPoint &offset, bool canUseSrgb)
-{
-    const QRect clipRect = textures->clipRect(idx);
-    if (clipRect.isEmpty())
-        return;
-
-    QRect rectInWindow = textures->geometry(idx);
-    // relative to the TLW, not necessarily our window (if the flush is for a native child widget), have to adjust
-    rectInWindow.translate(-offset);
-
-    const QRect clippedRectInWindow = rectInWindow & clipRect.translated(rectInWindow.topLeft());
-    const QRect srcRect = toBottomLeftRect(clipRect, rectInWindow.height());
-
-    const QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(deviceRect(clippedRectInWindow, window),
-                                                                     deviceWindowRect);
-
-    const QMatrix3x3 source = QOpenGLTextureBlitter::sourceTransform(deviceRect(srcRect, window),
-                                                                     deviceRect(rectInWindow, window).size(),
-                                                                     QOpenGLTextureBlitter::OriginBottomLeft);
-
-    QOpenGLFunctions *funcs = QOpenGLContext::currentContext()->functions();
-    const bool srgb = textures->flags(idx).testFlag(QPlatformTextureList::TextureIsSrgb);
-    if (srgb && canUseSrgb)
-        funcs->glEnable(GL_FRAMEBUFFER_SRGB);
-
-    blitter->blit(textures->textureId(idx), target, source);
-
-    if (srgb && canUseSrgb)
-        funcs->glDisable(GL_FRAMEBUFFER_SRGB);
-}
-
 /*!
     Flushes the given \a region from the specified \a window onto the
     screen, and composes it with the specified \a textures.
 
-    The default implementation retrieves the contents using toTexture()
+    If OpenGLSupport has been enabled using \c setOpenGLSupport,
+    the default implementation retrieves the contents using toTexture()
     and composes using OpenGL. May be reimplemented in subclasses if there
     is a more efficient native way to do it.
 
     \note \a region is relative to the window which may not be top-level in case
     \a window corresponds to a native child widget. \a offset is the position of
     the native child relative to the top-level window.
+
+    \sa setOpenGLSupport()
  */
 
 void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &region,
@@ -324,162 +207,13 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
                                             QPlatformTextureList *textures,
                                             bool translucentBackground)
 {
-    if (!qt_window_private(window)->receivedExpose)
-        return;
-
-    if (!d_ptr->context) {
-        d_ptr->context.reset(new QOpenGLContext);
-        d_ptr->context->setFormat(d_ptr->window->requestedFormat());
-        d_ptr->context->setScreen(d_ptr->window->screen());
-        d_ptr->context->setShareContext(qt_window_private(d_ptr->window)->shareContext());
-        if (!d_ptr->context->create()) {
-            qCWarning(lcQpaBackingStore, "composeAndFlush: QOpenGLContext creation failed");
-            return;
-        }
-    }
-
-    bool current = d_ptr->context->makeCurrent(window);
-
-    if (!current && !d_ptr->context->isValid()) {
-        delete d_ptr->blitter;
-        d_ptr->blitter = nullptr;
-        d_ptr->textureId = 0;
-        current = d_ptr->context->create() && d_ptr->context->makeCurrent(window);
-    }
-
-    if (!current) {
-        qCWarning(lcQpaBackingStore, "composeAndFlush: makeCurrent() failed");
-        return;
-    }
-
-    qCDebug(lcQpaBackingStore) << "Composing and flushing" << region << "of" << window
-        << "at offset" << offset << "with" << textures->count() << "texture(s) in" << textures;
-
-    QWindowPrivate::get(window)->lastComposeTime.start();
-
-    QOpenGLFunctions *funcs = d_ptr->context->functions();
-    funcs->glViewport(0, 0, qRound(window->width() * window->devicePixelRatio()), qRound(window->height() * window->devicePixelRatio()));
-    funcs->glClearColor(0, 0, 0, translucentBackground ? 0 : 1);
-    funcs->glClear(GL_COLOR_BUFFER_BIT);
-
-    if (!d_ptr->blitter) {
-        d_ptr->blitter = new QOpenGLTextureBlitter;
-        d_ptr->blitter->create();
-    }
-
-    d_ptr->blitter->bind();
-
-    const QRect deviceWindowRect = deviceRect(QRect(QPoint(), window->size()), window);
-    const QPoint deviceWindowOffset = deviceOffset(offset, window);
-
-    bool canUseSrgb = false;
-    // If there are any sRGB textures in the list, check if the destination
-    // framebuffer is sRGB capable.
-    for (int i = 0; i < textures->count(); ++i) {
-        if (textures->flags(i).testFlag(QPlatformTextureList::TextureIsSrgb)) {
-            GLint cap = 0;
-            funcs->glGetIntegerv(GL_FRAMEBUFFER_SRGB_CAPABLE, &cap);
-            if (cap)
-                canUseSrgb = true;
-            break;
-        }
-    }
-
-    // Textures for renderToTexture widgets.
-    for (int i = 0; i < textures->count(); ++i) {
-        if (!textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop))
-            blitTextureForWidget(textures, i, window, deviceWindowRect, d_ptr->blitter, offset, canUseSrgb);
-    }
-
-    // Backingstore texture with the normal widgets.
-    GLuint textureId = 0;
-    QOpenGLTextureBlitter::Origin origin = QOpenGLTextureBlitter::OriginTopLeft;
-    if (QPlatformGraphicsBuffer *graphicsBuffer = this->graphicsBuffer()) {
-        if (graphicsBuffer->size() != d_ptr->textureSize) {
-            if (d_ptr->textureId)
-                funcs->glDeleteTextures(1, &d_ptr->textureId);
-            funcs->glGenTextures(1, &d_ptr->textureId);
-            funcs->glBindTexture(GL_TEXTURE_2D, d_ptr->textureId);
-            QOpenGLContext *ctx = QOpenGLContext::currentContext();
-            if (!ctx->isOpenGLES() || ctx->format().majorVersion() >= 3) {
-                funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
-                funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
-            }
-            funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
-            funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
-            funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
-            funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
-
-            if (QPlatformGraphicsBufferHelper::lockAndBindToTexture(graphicsBuffer, &d_ptr->needsSwizzle, &d_ptr->premultiplied)) {
-                d_ptr->textureSize = graphicsBuffer->size();
-            } else {
-                d_ptr->textureSize = QSize(0,0);
-            }
-
-            graphicsBuffer->unlock();
-        } else if (!region.isEmpty()){
-            funcs->glBindTexture(GL_TEXTURE_2D, d_ptr->textureId);
-            QPlatformGraphicsBufferHelper::lockAndBindToTexture(graphicsBuffer, &d_ptr->needsSwizzle, &d_ptr->premultiplied);
-            graphicsBuffer->unlock();
-        }
-
-        if (graphicsBuffer->origin() == QPlatformGraphicsBuffer::OriginBottomLeft)
-            origin = QOpenGLTextureBlitter::OriginBottomLeft;
-        textureId = d_ptr->textureId;
-    } else {
-        TextureFlags flags;
-        textureId = toTexture(deviceRegion(region, window, offset), &d_ptr->textureSize, &flags);
-        d_ptr->needsSwizzle = (flags & TextureSwizzle) != 0;
-        d_ptr->premultiplied = (flags & TexturePremultiplied) != 0;
-        if (flags & TextureFlip)
-            origin = QOpenGLTextureBlitter::OriginBottomLeft;
-    }
-
-    funcs->glEnable(GL_BLEND);
-    if (d_ptr->premultiplied)
-        funcs->glBlendFuncSeparate(GL_ONE, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
+    if (auto *c = d_ptr->openGLSupport)
+        c->composeAndFlush(window, region, offset, textures, translucentBackground);
     else
-        funcs->glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
-
-    if (textureId) {
-        if (d_ptr->needsSwizzle)
-            d_ptr->blitter->setRedBlueSwizzle(true);
-        // The backingstore is for the entire tlw.
-        // In case of native children offset tells the position relative to the tlw.
-        const QRect srcRect = toBottomLeftRect(deviceWindowRect.translated(deviceWindowOffset), d_ptr->textureSize.height());
-        const QMatrix3x3 source = QOpenGLTextureBlitter::sourceTransform(srcRect,
-                                                                         d_ptr->textureSize,
-                                                                         origin);
-        d_ptr->blitter->blit(textureId, QMatrix4x4(), source);
-        if (d_ptr->needsSwizzle)
-            d_ptr->blitter->setRedBlueSwizzle(false);
-    }
-
-    // Textures for renderToTexture widgets that have WA_AlwaysStackOnTop set.
-    bool blendIsPremultiplied = d_ptr->premultiplied;
-    for (int i = 0; i < textures->count(); ++i) {
-        const QPlatformTextureList::Flags flags = textures->flags(i);
-        if (flags.testFlag(QPlatformTextureList::NeedsPremultipliedAlphaBlending)) {
-            if (!blendIsPremultiplied) {
-                funcs->glBlendFuncSeparate(GL_ONE, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
-                blendIsPremultiplied = true;
-            }
-        } else {
-            if (blendIsPremultiplied) {
-                funcs->glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
-                blendIsPremultiplied = false;
-            }
-        }
-        if (flags.testFlag(QPlatformTextureList::StacksOnTop))
-            blitTextureForWidget(textures, i, window, deviceWindowRect, d_ptr->blitter, offset, canUseSrgb);
-    }
-
-    funcs->glDisable(GL_BLEND);
-    d_ptr->blitter->release();
-
-    d_ptr->context->swapBuffers(window);
+        qWarning() << Q_FUNC_INFO << "no opengl support set";
 }
 #endif
+
 /*!
   Implemented in subclasses to return the content of the backingstore as a QImage.
 
@@ -504,7 +238,8 @@ QImage QPlatformBackingStore::toImage() const
   The ownership of the texture is not transferred. The caller must not store
   the return value between calls, but instead call this function before each use.
 
-  The default implementation returns a cached texture if \a dirtyRegion is empty and
+  If OpenGLSupport has been enabled using \c setOpenGLSupport,
+  the default implementation returns a cached texture if \a dirtyRegion is empty and
   \a textureSize matches the backingstore size, otherwise it retrieves the content using
   toImage() and performs a texture upload. This works only if the value of \a textureSize
   is preserved between the calls to this function.
@@ -520,141 +255,17 @@ QImage QPlatformBackingStore::toImage() const
   flags will be set to include \c TextureFlip.
 
   \note \a dirtyRegion is relative to the backingstore so no adjustment is needed.
+
+  \sa setOpenGLSupport()
  */
 GLuint QPlatformBackingStore::toTexture(const QRegion &dirtyRegion, QSize *textureSize, TextureFlags *flags) const
 {
-    Q_ASSERT(textureSize);
-    Q_ASSERT(flags);
-
-    QImage image = toImage();
-    QSize imageSize = image.size();
-
-    QOpenGLContext *ctx = QOpenGLContext::currentContext();
-    GLenum internalFormat = GL_RGBA;
-    GLuint pixelType = GL_UNSIGNED_BYTE;
-
-    bool needsConversion = false;
-    *flags = { };
-    switch (image.format()) {
-    case QImage::Format_ARGB32_Premultiplied:
-        *flags |= TexturePremultiplied;
-        Q_FALLTHROUGH();
-    case QImage::Format_RGB32:
-    case QImage::Format_ARGB32:
-        *flags |= TextureSwizzle;
-        break;
-    case QImage::Format_RGBA8888_Premultiplied:
-        *flags |= TexturePremultiplied;
-        Q_FALLTHROUGH();
-    case QImage::Format_RGBX8888:
-    case QImage::Format_RGBA8888:
-        break;
-    case QImage::Format_BGR30:
-    case QImage::Format_A2BGR30_Premultiplied:
-        if (!ctx->isOpenGLES() || ctx->format().majorVersion() >= 3) {
-            pixelType = GL_UNSIGNED_INT_2_10_10_10_REV;
-            internalFormat = GL_RGB10_A2;
-            *flags |= TexturePremultiplied;
-        } else {
-            needsConversion = true;
-        }
-        break;
-    case QImage::Format_RGB30:
-    case QImage::Format_A2RGB30_Premultiplied:
-        if (!ctx->isOpenGLES() || ctx->format().majorVersion() >= 3) {
-            pixelType = GL_UNSIGNED_INT_2_10_10_10_REV;
-            internalFormat = GL_RGB10_A2;
-            *flags |= TextureSwizzle | TexturePremultiplied;
-        } else {
-            needsConversion = true;
-        }
-        break;
-    default:
-        needsConversion = true;
-        break;
-    }
-    if (imageSize.isEmpty()) {
-        *textureSize = imageSize;
+    if (auto *c = d_ptr->openGLSupport)
+        return c->toTexture(dirtyRegion, textureSize, flags);
+    else {
+        qWarning() << Q_FUNC_INFO << "no opengl support set";
         return 0;
     }
-
-    // Must rely on the input only, not d_ptr.
-    // With the default composeAndFlush() textureSize is &d_ptr->textureSize.
-    bool resized = *textureSize != imageSize;
-    if (dirtyRegion.isEmpty() && !resized)
-        return d_ptr->textureId;
-
-    *textureSize = imageSize;
-
-    if (needsConversion)
-        image = image.convertToFormat(QImage::Format_RGBA8888);
-
-    // The image provided by the backingstore may have a stride larger than width * 4, for
-    // instance on platforms that manually implement client-side decorations.
-    static const int bytesPerPixel = 4;
-    const int strideInPixels = image.bytesPerLine() / bytesPerPixel;
-    const bool hasUnpackRowLength = !ctx->isOpenGLES() || ctx->format().majorVersion() >= 3;
-
-    QOpenGLFunctions *funcs = ctx->functions();
-
-    if (hasUnpackRowLength) {
-        funcs->glPixelStorei(GL_UNPACK_ROW_LENGTH, strideInPixels);
-    } else if (strideInPixels != image.width()) {
-        // No UNPACK_ROW_LENGTH on ES 2.0 and yet we would need it. This case is typically
-        // hit with QtWayland which is rarely used in combination with a ES2.0-only GL
-        // implementation.  Therefore, accept the performance hit and do a copy.
-        image = image.copy();
-    }
-
-    if (resized) {
-        if (d_ptr->textureId)
-            funcs->glDeleteTextures(1, &d_ptr->textureId);
-        funcs->glGenTextures(1, &d_ptr->textureId);
-        funcs->glBindTexture(GL_TEXTURE_2D, d_ptr->textureId);
-        if (!ctx->isOpenGLES() || ctx->format().majorVersion() >= 3) {
-            funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
-            funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
-        }
-        funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
-        funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
-        funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
-        funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
-
-        funcs->glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, imageSize.width(), imageSize.height(), 0, GL_RGBA, pixelType,
-                            const_cast<uchar*>(image.constBits()));
-    } else {
-        funcs->glBindTexture(GL_TEXTURE_2D, d_ptr->textureId);
-        QRect imageRect = image.rect();
-        QRect rect = dirtyRegion.boundingRect() & imageRect;
-
-        if (hasUnpackRowLength) {
-            funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, rect.x(), rect.y(), rect.width(), rect.height(), GL_RGBA, pixelType,
-                                   image.constScanLine(rect.y()) + rect.x() * bytesPerPixel);
-        } else {
-            // if the rect is wide enough it's cheaper to just
-            // extend it instead of doing an image copy
-            if (rect.width() >= imageRect.width() / 2) {
-                rect.setX(0);
-                rect.setWidth(imageRect.width());
-            }
-
-            // if the sub-rect is full-width we can pass the image data directly to
-            // OpenGL instead of copying, since there's no gap between scanlines
-
-            if (rect.width() == imageRect.width()) {
-                funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, 0, rect.y(), rect.width(), rect.height(), GL_RGBA, pixelType,
-                                       image.constScanLine(rect.y()));
-            } else {
-                funcs->glTexSubImage2D(GL_TEXTURE_2D, 0, rect.x(), rect.y(), rect.width(), rect.height(), GL_RGBA, pixelType,
-                                       image.copy(rect).constBits());
-            }
-        }
-    }
-
-    if (hasUnpackRowLength)
-        funcs->glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
-
-    return d_ptr->textureId;
 }
 #endif // QT_NO_OPENGL
 
@@ -706,6 +317,18 @@ QBackingStore *QPlatformBackingStore::backingStore() const
     return d_ptr->backingStore;
 }
 
+#ifndef QT_NO_OPENGL
+/*!
+    Injects an OpenGL implementation helper. Platform integrations need to
+    call this if they intend to use the default OpenGL implementations of
+    composeAndFlush or toTexture.
+*/
+void QPlatformBackingStore::setOpenGLSupport(QPlatformBackingStoreOpenGLSupportBase *openGLSupport)
+{
+    d_ptr->openGLSupport = openGLSupport;
+}
+#endif // QT_NO_OPENGL
+
 /*!
     This function is called before painting onto the surface begins,
     with the \a region in which the painting will occur.