render the themes when the screen size changed

openlp/core/ui/mainwindow.py

@@ -783,6 +783,7 @@ class MainWindow(QtGui.QMainWindow, Ui_MainWindow):
         self.renderer.update_display()
         self.liveController.screenSizeChanged()
         self.previewController.screenSizeChanged()
+        self.themeManagerContents.updatePreviewImages()
         self.setFocus()
         self.activateWindow()
 

openlp/core/ui/thememanager.py

@@ -660,6 +660,15 @@ class ThemeManager(QtGui.QWidget):
         pixmap.save(thumb, u'png')
         log.debug(u'Theme image written to %s', samplepathname)
 
+    def updatePreviewImages(self):
+        """
+        Called to update the themes' preview images.
+        """
+        for theme in self.themelist:
+            self.generateAndSaveImage(
+                self.path, theme, self.getThemeData(theme))
+        self.loadThemes()
+
     def generateImage(self, themeData, forcePage=False):
         """
         Call the renderer to build a Sample Image