don't risk to mix up frames with different pixelratio

BUG:345155
Change-Id: I0b2384831d755e02b944a49259ffeacd0d2fb71e

src/plasma/framesvg.cpp

@@ -236,6 +236,9 @@ void FrameSvg::setElementPrefix(const QString &prefix)
             if (!oldFrameData->frameSize.isEmpty()) {
                 const QString key = d->cacheId(oldFrameData, d->prefix);
                 newFd = FrameSvgPrivate::s_sharedFrames[theme()->d].value(key);
+                if (newFd && newFd->devicePixelRatio != devicePixelRatio()) {
+                    newFd = 0;
+                }
             }
 
             // we need to put this in the cache if we didn't find it in the shared frames

src/plasma/private/framesvg_p.h

@@ -68,6 +68,7 @@ public:
           leftMargin(0),
           rightMargin(0),
           bottomMargin(0),
+          devicePixelRatio(svg->devicePixelRatio()),
           noBorderPadding(false),
           stretchBorders(false),
           tileCenter(false),
@@ -116,6 +117,8 @@ public:
     int fixedRightMargin;
     int fixedBottomMargin;
 
+    qreal devicePixelRatio;
+
     //size of the svg where the size of the "center"
     //element is contentWidth x contentHeight
     bool noBorderPadding : 1;

src/plasma/svg.cpp

@@ -709,6 +709,10 @@ void Svg::setDevicePixelRatio(qreal ratio)
         return;
     }
 
+    if (FrameSvg *f = qobject_cast<FrameSvg *>(this)) {
+        f->clearCache();
+    }
+
     d->devicePixelRatio = floor(ratio);
 
     emit repaintNeeded();