Lazy rendering of message contents

Message will render as user is scrolling down. This prevents interface
freezes on long messages (such as inline img in text mode). Fixes
Bitmessage##366

Also a minor fix in text mode rendering.

src/bitmessageqt/messageview.py

@@ -17,6 +17,11 @@ class MessageView(QtGui.QTextBrowser):
         self.setOpenExternalLinks(False)
         self.setOpenLinks(False)
         self.anchorClicked.connect(self.confirmURL)
+        self.out = ""
+        self.outpos = 0
+        self.document().setUndoRedoEnabled(False)
+        self.rendering = False
+        self.verticalScrollBar().valueChanged.connect(self.lazyRender)
     
     def mousePressEvent(self, event):
         #text = textCursor.block().text()
@@ -36,22 +41,49 @@ class MessageView(QtGui.QTextBrowser):
         if reply == QtGui.QMessageBox.Yes:
             QtGui.QDesktopServices.openUrl(link)
 
+    def lazyRender(self):
+        if self.rendering:
+            return
+        self.rendering = True
+        position = self.verticalScrollBar().value()
+        cursor = QtGui.QTextCursor(self.document())
+        while self.outpos < len(self.out) and self.verticalScrollBar().value() >= self.document().size().height() - 2 * self.size().height():
+            startpos = self.outpos
+            self.outpos += 10240
+            # find next end of tag
+            if self.mode == MessageView.MODE_HTML:
+                pos = self.out.find(">", self.outpos)
+                if pos > self.outpos:
+                    self.outpos = pos
+            cursor.movePosition(QtGui.QTextCursor.End, QtGui.QTextCursor.MoveAnchor)
+            cursor.insertHtml(QtCore.QString(self.out[startpos:self.outpos]))
+        self.verticalScrollBar().setValue(position)
+        self.rendering = False
+    
     def showPlain(self):
         self.mode = MessageView.MODE_PLAIN
         out = self.html.raw
         if self.html.has_html:
-            out = "<div align=\"center\" style=\"text-decoration: underline;\"><b>" + QtGui.QApplication.translate(type(self).__name__, MessageView.TEXT_PLAIN) + "</b></div><br/>" + out
-        self.setHtml(QtCore.QString(out))
+            out = "<div align=\"center\" style=\"text-decoration: underline;\"><b>" + str(QtGui.QApplication.translate(type(self).__name__, MessageView.TEXT_PLAIN)) + "</b></div><br/>" + out
+        self.out = out
+        self.outpos = 0
+        self.setHtml("")
+        self.lazyRender()
 
     def showHTML(self):
         self.mode = MessageView.MODE_HTML
         out = self.html.sanitised
-        out = "<div align=\"center\" style=\"text-decoration: underline;\"><b>" + QtGui.QApplication.translate(type(self).__name__, MessageView.TEXT_HTML) + "</b></div><br/>" + out
-        self.setHtml(QtCore.QString(out))
+        out = "<div align=\"center\" style=\"text-decoration: underline;\"><b>" + str(QtGui.QApplication.translate(type(self).__name__, MessageView.TEXT_HTML)) + "</b></div><br/>" + out
+        self.out = out
+        self.outpos = 0
+        self.setHtml("")
+        self.lazyRender()
 
     def setContent(self, data):
         self.html = SafeHTMLParser()
         self.html.allow_picture = True
+        self.html.reset()
+        self.html.reset_safe()
         self.html.feed(data)
         self.html.close()
-        self.showPlain()
+        self.showPlain()

src/bitmessageqt/safehtmlparser.py

@@ -25,8 +25,10 @@ class SafeHTMLParser(HTMLParser):
         self.has_html = False
         
     def reset_safe(self):
+        self.elements = set()
         self.raw = u""
         self.sanitised = u""
+        self.has_html = False
 
     def add_if_acceptable(self, tag, attrs = None):
         if not tag in self.acceptable_elements:
@@ -35,12 +37,12 @@ class SafeHTMLParser(HTMLParser):
         if inspect.stack()[1][3] == "handle_endtag":
             self.sanitised += "/"
         self.sanitised += tag
-        if attrs is not None:
+        if not attrs is None:
             for attr in attrs:
                 if tag == "img" and attr[0] == "src" and not self.allow_picture:
                     attr[1] = ""
                 self.sanitised += " " + quote_plus(attr[0])
-                if attr[1] is not None:
+                if not (attr[1] is None):
                     self.sanitised += "=\"" + attr[1] + "\""
         if inspect.stack()[1][3] == "handle_startendtag":
             self.sanitised += "/"
@@ -51,13 +53,13 @@ class SafeHTMLParser(HTMLParser):
         if inspect.stack()[1][3] == "handle_endtag":
             self.raw += "/"
         self.raw += tag
-        if attrs is not None:
+        if not attrs is None:
             for attr in attrs:
                 if tag == "img" and attr[0] == "src" and not self.allow_picture:
                     attr[1] = ""
                 self.raw += " " + attr[0]
-                if attr[1] is not None:
-                    self.raw + "="" + attr[1] + """
+                if not (attr[1] is None):
+                    self.raw += "="" + attr[1] + """
         if inspect.stack()[1][3] == "handle_startendtag":
             self.raw += "/"
         self.raw += ">"