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

1 files changed, 27 insertions, 0 deletions

diff --git a/src/openvg/qwindowsurface_vgegl.cpp b/src/openvg/qwindowsurface_vgegl.cpp
index 46a905f..99b614b 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