From d78d263996aa737571b853dade0475e929d0ca48 Mon Sep 17 00:00:00 2001
From: tassaron <rutachigal@gmail.com>
Date: Sun, 6 Aug 2017 10:10:04 -0400
Subject: [PATCH] try to fix flickering live preview during export

by temporarily asking Qt not to clear the widget's paint region
---
 src/mainwindow.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/mainwindow.py b/src/mainwindow.py
index 1c8806d..825b5bc 100644
--- a/src/mainwindow.py
+++ b/src/mainwindow.py
@@ -31,6 +31,7 @@ class PreviewWindow(QtWidgets.QLabel):
         self.parent = parent
         self.setFrameStyle(QtWidgets.QFrame.StyledPanel)
         self.pixmap = QtGui.QPixmap(img)
+        self.isFlickering = 0
 
     def paintEvent(self, event):
         size = self.size()
@@ -47,9 +48,23 @@ class PreviewWindow(QtWidgets.QLabel):
         painter.drawPixmap(point, scaledPix)
 
     def changePixmap(self, img):
+        if self.parent.encoding:
+            # track time to determine if the preview is flickering due to lag
+            bTime = time.time()
+        elif self.isFlickering > 0:
+            # no longer exporting video so reset the paint area to normal
+            self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent, False)
+            self.isFlickering = 0
+
         self.pixmap = QtGui.QPixmap(img)
         self.repaint()
 
+        if self.parent.encoding and time.time() - bTime > 1.1:
+            self.isFlickering += 1
+        if self.isFlickering == 8:
+            # if export is lagging, temporarily disable clearing the paint area
+            self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent, True)
+
     @QtCore.pyqtSlot(str)
     def threadError(self, msg):
         self.parent.showMessage(