Implement OpenVG buffer scrolling and enable it on Symbian.

Add support for accelerated scrolling in the "direct" window surface
implementation. Using vgCopyPixels(), the already rasterized content on
the surface can be shifted to a new location such that only a portion
of the suqsequent frame needs to be repainted instead of the entire
frame.

This only works when the "preserved" EGL swap behavior is enabled and
the impact on performance is highly dependant on the specific hardware
platform in use.

Task-number: QT-2972
Reviewed-by: Rhys Weatherley

4 files changed, 36 insertions, 2 deletions

diff --git a/src/openvg/openvg.pro b/src/openvg/openvg.pro
index 3790492cb2..883f0f3f0d 100644
--- a/src/openvg/openvg.pro
+++ b/src/openvg/openvg.pro
@@ -33,7 +33,7 @@ contains(QT_CONFIG, egl) {
         qwindowsurface_vgegl.cpp
 }
 
-symbian: DEFINES += QVG_RECREATE_ON_SIZE_CHANGE
+symbian: DEFINES += QVG_RECREATE_ON_SIZE_CHANGE QVG_BUFFER_SCROLLING
 
 include(../qbase.pri)
 
diff --git a/src/openvg/qwindowsurface_vg.cpp b/src/openvg/qwindowsurface_vg.cpp
index 83b0764bd3..c19d5d1afe 100644
--- a/src/openvg/qwindowsurface_vg.cpp
+++ b/src/openvg/qwindowsurface_vg.cpp
@@ -57,6 +57,7 @@ QVGWindowSurface::QVGWindowSurface(QWidget *window)
 {
     // Create the default type of EGL window surface for windows.
     d_ptr = new QVGEGLWindowSurfaceDirect(this);
+    setStaticContentsSupport(d_ptr->supportsStaticContents());
 }
 
 QVGWindowSurface::QVGWindowSurface
@@ -89,7 +90,9 @@ void QVGWindowSurface::setGeometry(const QRect &rect)
 
 bool QVGWindowSurface::scroll(const QRegion &area, int dx, int dy)
 {
-    return QWindowSurface::scroll(area, dx, dy);
+    if (!d_ptr->scroll(window(), area, dx, dy))
+        return QWindowSurface::scroll(area, dx, dy);
+    return true;
 }
 
 void QVGWindowSurface::beginPaint(const QRegion &region)
diff --git a/src/openvg/qwindowsurface_vgegl.cpp b/src/openvg/qwindowsurface_vgegl.cpp
index 46a905fca9..99b614b6b2 100644
--- a/src/openvg/qwindowsurface_vgegl.cpp
+++ b/src/openvg/qwindowsurface_vgegl.cpp
@@ -758,6 +758,33 @@ void QVGEGLWindowSurfaceDirect::endPaint
     }
 }
 
+bool QVGEGLWindowSurfaceDirect::supportsStaticContents() const
+{
+#if defined(QVG_BUFFER_SCROLLING) && !defined(QVG_NO_PRESERVED_SWAP)
+    return true;
+#else
+    return QVGEGLWindowSurfacePrivate::supportsStaticContents();
+#endif
+}
+
+bool QVGEGLWindowSurfaceDirect::scroll(QWidget *widget, const QRegion& area, int dx, int dy)
+{
+#ifdef QVG_BUFFER_SCROLLING
+    QEglContext *context = ensureContext(widget);
+    if (context) {
+        context->makeCurrent(windowSurface);
+        QRect scrollRect = area.boundingRect();
+        int sx = scrollRect.x();
+        int sy = size.height() - scrollRect.y() - scrollRect.height();
+        vgSeti(VG_SCISSORING, VG_FALSE);
+        vgCopyPixels(sx + dx, sy - dy, sx, sy, scrollRect.width(), scrollRect.height());
+        context->lazyDoneCurrent();
+        return true;
+    }
+#endif
+    return false;
+}
+
 QT_END_NAMESPACE
 
 #endif
diff --git a/src/openvg/qwindowsurface_vgegl_p.h b/src/openvg/qwindowsurface_vgegl_p.h
index aa0c648a4e..892fd9d929 100644
--- a/src/openvg/qwindowsurface_vgegl_p.h
+++ b/src/openvg/qwindowsurface_vgegl_p.h
@@ -77,6 +77,8 @@ public:
         (QWidget *widget, const QRegion& region, QImage *image = 0) = 0;
     virtual VGImage surfaceImage() const;
     virtual QSize surfaceSize() const = 0;
+    virtual bool supportsStaticContents() const { return false; }
+    virtual bool scroll(QWidget *, const QRegion&, int, int) { return false; }
 
 private:
     QVGPaintEngine *engine;
@@ -128,6 +130,8 @@ public:
     void beginPaint(QWidget *widget);
     void endPaint(QWidget *widget, const QRegion& region, QImage *image);
     QSize surfaceSize() const { return size; }
+    bool supportsStaticContents() const;
+    bool scroll(QWidget *widget, const QRegion& area, int dx, int dy);
 
 protected:
     QEglContext *context;