Minimal ABI necessary for future optimized QPixmap

Add virtual hooks that can make it possible in Qt6 to implement paint
device specific pixmaps.

Change-Id: Ib1d1d7b5e32d9430203f718534344b25c0ead744
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

src/gui/painting/qpaintengine.cpp

@@ -44,10 +44,13 @@
 #include <qdebug.h>
 #include <qmath.h>
 #include <qguiapplication.h>
-#include <private/qtextengine_p.h>
 #include <qvarlengtharray.h>
+#include <qpa/qplatformintegration.h>
+#include <qpa/qplatformpixmap.h>
 #include <private/qfontengine_p.h>
+#include <private/qguiapplication_p.h>
 #include <private/qpaintengineex_p.h>
+#include <private/qtextengine_p.h>
 
 
 QT_BEGIN_NAMESPACE
@@ -994,6 +997,43 @@ QRect QPaintEngine::systemRect() const
     return d_func()->systemRect;
 }
 
+/*!
+    \internal
+
+    Creates a QPixmap optimized for this paint engine and device.
+*/
+QPixmap QPaintEngine::createPixmap(QSize size)
+{
+    if (Q_UNLIKELY(!qobject_cast<QGuiApplication *>(QCoreApplication::instance()))) {
+        qWarning("QPaintEngine::createPixmap: QPixmap cannot be created without a QGuiApplication");
+        return QPixmap();
+    }
+
+    QScopedPointer<QPlatformPixmap> data(QGuiApplicationPrivate::platformIntegration()->createPlatformPixmap(QPlatformPixmap::PixmapType));
+    data->resize(size.width(), size.height());
+    return QPixmap(data.take());
+}
+
+/*!
+    \internal
+
+    Creates a QPixmap optimized for this paint engine and device.
+*/
+QPixmap QPaintEngine::createPixmapFromImage(QImage image, Qt::ImageConversionFlags flags)
+{
+    if (Q_UNLIKELY(!qobject_cast<QGuiApplication *>(QCoreApplication::instance()))) {
+        qWarning("QPaintEngine::createPixmapFromImage: QPixmap cannot be created without a QGuiApplication");
+        return QPixmap();
+    }
+
+    QScopedPointer<QPlatformPixmap> data(QGuiApplicationPrivate::platformIntegration()->createPlatformPixmap(QPlatformPixmap::PixmapType));
+    if (image.isDetached())
+        data->fromImageInPlace(image, flags);
+    else
+        data->fromImage(image, flags);
+    return QPixmap(data.take());
+}
+
 QPaintEnginePrivate::~QPaintEnginePrivate()
 {
 }

src/gui/painting/qpaintengine.h

@@ -225,6 +225,9 @@ public:
     void syncState();
     inline bool isExtended() const { return extended; }
 
+    virtual QPixmap createPixmap(QSize size);
+    virtual QPixmap createPixmapFromImage(QImage image, Qt::ImageConversionFlags flags = Qt::AutoColor);
+
 protected:
     QPaintEngine(QPaintEnginePrivate &data, PaintEngineFeatures devcaps=PaintEngineFeatures());