Improve scrolling in DirectFB

Since DirectFB always uses the front buffer of a double buffered surface
as the source when blitting we needed to make sure that the front buffer
was valid and hence we called Flip for each scroll. This had negative
performance impacts since you could end up with various parts of a
window being updated at different times.

With this patch we store whether the front-buffer is up to date inside
the window surface and only call Flip in scroll if it's not.

Reviewed-by: Jervey Kong <jervey.kong@nokia.com>

2 files changed, 13 insertions, 17 deletions

diff --git a/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.cpp b/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.cpp
index a8bdb65..51969fc 100644
--- a/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.cpp
+++ b/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.cpp
@@ -61,6 +61,7 @@ QDirectFBWindowSurface::QDirectFBWindowSurface(DFBSurfaceFlipFlags flip, QDirect
 #endif
     , flipFlags(flip)
     , boundingRectFlip(scr->directFBFlags() & QDirectFBScreen::BoundingRectFlip)
+    , flushPending(false)
 {
 #ifdef QT_NO_DIRECTFB_WM
     mode = Offscreen;
@@ -80,6 +81,7 @@ QDirectFBWindowSurface::QDirectFBWindowSurface(DFBSurfaceFlipFlags flip, QDirect
 #endif
     , flipFlags(flip)
     , boundingRectFlip(scr->directFBFlags() & QDirectFBScreen::BoundingRectFlip)
+    , flushPending(false)
 {
     SurfaceFlags flags = 0;
     if (!widget || widget->window()->windowOpacity() == 0xff)
@@ -299,28 +301,19 @@ void QDirectFBWindowSurface::setPermanentState(const QByteArray &state)
     }
 }
 
-static inline void scrollSurface(IDirectFBSurface *surface, const QRect &r, int dx, int dy)
-{
-    const DFBRectangle rect = { r.x(), r.y(), r.width(), r.height() };
-    surface->Blit(surface, surface, &rect, r.x() + dx, r.y() + dy);
-    const DFBRegion region = { rect.x + dx, rect.y + dy, r.right() + dx, r.bottom() + dy };
-    surface->Flip(surface, &region, DSFLIP_BLIT);
-}
-
 bool QDirectFBWindowSurface::scroll(const QRegion &region, int dx, int dy)
 {
-    if (!dfbSurface || !(flipFlags & DSFLIP_BLIT) || region.isEmpty())
+    if (!dfbSurface || !(flipFlags & DSFLIP_BLIT) || region.rectCount() != 1)
         return false;
-    dfbSurface->SetBlittingFlags(dfbSurface, DSBLIT_NOFX);
-    if (region.rectCount() == 1) {
-        scrollSurface(dfbSurface, region.boundingRect(), dx, dy);
+    if (flushPending) {
+        dfbSurface->Flip(dfbSurface, 0, DSFLIP_BLIT);
     } else {
-        const QVector<QRect> rects = region.rects();
-        const int n = rects.size();
-        for (int i=0; i<n; ++i) {
-            scrollSurface(dfbSurface, rects.at(i), dx, dy);
-        }
+        flushPending = true;
     }
+    dfbSurface->SetBlittingFlags(dfbSurface, DSBLIT_NOFX);
+    const QRect r = region.boundingRect();
+    const DFBRectangle rect = { r.x(), r.y(), r.width(), r.height() };
+    dfbSurface->Blit(dfbSurface, dfbSurface, &rect, r.x() + dx, r.y() + dy);
     return true;
 }
 
@@ -384,6 +377,7 @@ void QDirectFBWindowSurface::flush(QWidget *widget, const QRegion &region,
         timer.restart();
     }
 #endif
+    flushPending = false;
 }
 
 void QDirectFBWindowSurface::beginPaint(const QRegion &)
@@ -391,6 +385,7 @@ void QDirectFBWindowSurface::beginPaint(const QRegion &)
     if (!engine) {
         engine = new QDirectFBPaintEngine(this);
     }
+    flushPending = true;
 }
 
 void QDirectFBWindowSurface::endPaint(const QRegion &)
diff --git a/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.h b/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.h
index a6138f6..4370a8f 100644
--- a/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.h
+++ b/src/plugins/gfxdrivers/directfb/qdirectfbwindowsurface.h
@@ -114,6 +114,7 @@ private:
 
     DFBSurfaceFlipFlags flipFlags;
     bool boundingRectFlip;
+    bool flushPending;
 #ifdef QT_DIRECTFB_TIMING
     int frames;
     QTime timer;