QS60Style: use placeholder texture when polishing widgets and palette

Background texture is not created until it is actually painted.
This allows skipping the whole background texture creation, if app
overwrites the QPalette::Window with its own data (image or color).

When widget is drawn and style notices that the widget is still using a
placeholder (1*1 red QPixmap) texture, it creates the real texture and
uses that for drawing.

Note that accessing QPalette::Window will give the placeholder pixmap.
Which is then again replaced with the real texture, if it is drawn
through the qt_s60_fill_background().

Task-number: QTBUG-14910
Reviewed-by: Laszlo Agocs

3 files changed, 33 insertions, 7 deletions

diff --git a/src/gui/styles/qs60style.cpp b/src/gui/styles/qs60style.cpp
index 15cb5c6..c100330 100644
--- a/src/gui/styles/qs60style.cpp
+++ b/src/gui/styles/qs60style.cpp
@@ -118,6 +118,7 @@ const short *QS60StylePrivate::m_pmPointer = QS60StylePrivate::data[0];
 
 // theme background texture
 QPixmap *QS60StylePrivate::m_background = 0;
+QPixmap *QS60StylePrivate::m_placeHolderTexture = 0;
 
 // theme palette
 QPalette *QS60StylePrivate::m_themePalette = 0;
@@ -155,6 +156,10 @@ const double KTabFontMul = 0.72;
 QS60StylePrivate::~QS60StylePrivate()
 {
     clearCaches(); //deletes also background image
+    if (m_placeHolderTexture) {
+        delete m_placeHolderTexture;
+        m_placeHolderTexture = 0;
+    }
     deleteThemePalette();
 #ifdef Q_WS_S60
     removeAnimations();
@@ -505,7 +510,10 @@ void QS60StylePrivate::setBackgroundTexture(QApplication *app) const
 {
     Q_UNUSED(app)
     QPalette applicationPalette = QApplication::palette();
-    applicationPalette.setBrush(QPalette::Window, backgroundTexture());
+    // The initial QPalette::Window is just a placeHolder QPixmap to save RAM
+    // if the actual texture is not needed. The real texture is created just before
+    // painting it in qt_s60_fill_background().
+    applicationPalette.setBrush(QPalette::Window, placeHolderTexture());
     setThemePalette(&applicationPalette);
 }
 
@@ -700,8 +708,10 @@ void QS60StylePrivate::setThemePalette(QPalette *palette) const
     palette->setColor(QPalette::LinkVisited, palette->color(QPalette::Link).darker());
     palette->setColor(QPalette::Highlight,
         s60Color(QS60StyleEnums::CL_QsnHighlightColors, 2, 0));
-    // set background image as a texture brush
-    palette->setBrush(QPalette::Window, backgroundTexture());
+    // The initial QPalette::Window is just a placeHolder QPixmap to save RAM
+    // if the actual texture is not needed. The real texture is created just before
+    // painting it in qt_s60_fill_background().
+    palette->setBrush(QPalette::Window, placeHolderTexture());
     // set as transparent so that styled full screen theme background is visible
     palette->setBrush(QPalette::Base, Qt::transparent);
     // set button color based on pixel colors
@@ -3529,10 +3539,12 @@ extern QPoint qt_s60_fill_background_offset(const QWidget *targetWidget);
 
 bool qt_s60_fill_background(QPainter *painter, const QRegion &rgn, const QBrush &brush)
 {
-    const QPixmap backgroundTexture(QS60StylePrivate::backgroundTexture());
-    if (backgroundTexture.cacheKey() != brush.texture().cacheKey())
+    const QPixmap placeHolder(QS60StylePrivate::placeHolderTexture());
+    if (placeHolder.cacheKey() != brush.texture().cacheKey())
         return false;
 
+    const QPixmap backgroundTexture(QS60StylePrivate::backgroundTexture());
+
     const QPaintDevice *target = painter->device();
     if (target->devType() == QInternal::Widget) {
         const QWidget *widget = static_cast<const QWidget *>(target);
diff --git a/src/gui/styles/qs60style_p.h b/src/gui/styles/qs60style_p.h
index c64cbb1..8c023bf 100644
--- a/src/gui/styles/qs60style_p.h
+++ b/src/gui/styles/qs60style_p.h
@@ -555,6 +555,7 @@ public:
     static QPixmap frame(SkinFrameElements frame, const QSize &size,
         SkinElementFlags flags = KDefaultSkinElementFlags);
     static QPixmap backgroundTexture();
+    static QPixmap placeHolderTexture();
 
 #ifdef Q_WS_S60
     void handleDynamicLayoutVariantSwitch();
@@ -614,6 +615,9 @@ private:
 
     // Contains background texture.
     static QPixmap *m_background;
+    // Placeholder pixmap for the real background texture.
+    static QPixmap *m_placeHolderTexture;
+
     const static SkinElementFlags KDefaultSkinElementFlags;
     // defined theme palette
     static QPalette *m_themePalette;
diff --git a/src/gui/styles/qs60style_s60.cpp b/src/gui/styles/qs60style_s60.cpp
index 8e442bf..1ff195d 100644
--- a/src/gui/styles/qs60style_s60.cpp
+++ b/src/gui/styles/qs60style_s60.cpp
@@ -66,7 +66,6 @@
 #include <aknnavi.h>
 #include <gulicon.h>
 #include <AknBitmapAnimation.h>
-
 #include <centralrepository.h>
 
 #if !defined(QT_NO_STYLE_S60) || defined(QT_PLUGIN)
@@ -1408,12 +1407,23 @@ QPixmap QS60StylePrivate::backgroundTexture()
 
     if (createNewBackground) {
         QPixmap background = part(QS60StyleEnums::SP_QsnBgScreen,
-                QSize(applicationRect.Width(), applicationRect.Height()), 0, SkinElementFlags());
+            QSize(applicationRect.Width(), applicationRect.Height()), 0, SkinElementFlags());
         m_background = new QPixmap(background);
     }
     return *m_background;
 }
 
+// Generates 1*1 red pixmap as a placeholder for real texture.
+// The actual theme texture is drawn in qt_s60_fill_background().
+QPixmap QS60StylePrivate::placeHolderTexture()
+{
+    if (!m_placeHolderTexture) {
+        m_placeHolderTexture = new QPixmap(1,1);
+        m_placeHolderTexture->fill(Qt::red);
+    }
+    return *m_placeHolderTexture;
+}
+
 QSize QS60StylePrivate::screenSize()
 {
     return QSize(S60->screenWidthInPixels, S60->screenHeightInPixels);