Smooth scrolling text in Qlabel - python-2.7

Question

I am trying to use a Qlabel as a message center for relaying messages to users of the application. Some messages might be longer than allowed for the Qlabel and I want it to just scroll horizontally until the end of the text. How can I do this in a Qlabel? I cannot seem to find anything in designer and don't want to work out some sort of truncation method in code that just takes off pieces from the front of the string, that seems silly.

Answer 1

What you are after is commonly known as Marquee widget. Here is a very simple and rusty implementation which make use of a QLabel, but it can be done with a QWidget too. I overridden the setText method from which i use a QTextDocument, with parent the QLabel itself, which holds the text. If the text is bigger than the size of the QLabel a QTimer triggers a translation method that moves the text:
import sys
from PyQt5.QtCore import QEvent, QTimer, pyqtSlot
from PyQt5.QtGui import QTextDocument, QPainter, QFontMetrics
from PyQt5.QtWidgets import QLabel, QApplication
class Marquee(QLabel):
x = 0
paused = False
document = None
speed = 50
timer = None
def __init__(self, parent=None):
super().__init__(parent)
self.fm = QFontMetrics(self.font())
self.setFixedSize(200, 20)
def setText(self, value):
self.x = 0
self.document = QTextDocument(self)
self.document.setPlainText(value)
# I multiplied by 1.06 because otherwise the text goes on 2 lines
self.document.setTextWidth(self.fm.width(value) * 1.06)
self.document.setUseDesignMetrics(True)
if self.document.textWidth() > self.width():
self.timer = QTimer(self)
self.timer.timeout.connect(self.translate)
self.timer.start((1 / self.speed) * 1000)
#pyqtSlot()
def translate(self):
if not self.paused:
if self.width() - self.x < self.document.textWidth():
self.x -= 1
else:
self.timer.stop()
self.repaint()
def event(self, event):
if event.type() == QEvent.Enter:
self.paused = True
elif event.type() == QEvent.Leave:
self.paused = False
return super().event(event)
def paintEvent(self, event):
if self.document:
p = QPainter(self)
p.translate(self.x, 0)
self.document.drawContents(p)
return super().paintEvent(event)
if __name__ == '__main__':
app = QApplication(sys.argv)
w = Marquee()
w.setText('Lorem ipsum dolor sit amet, consectetur adipiscing elit...')
w.show()
sys.exit(app.exec_())

Answer 2

With a little bit changing #Daniele Pantaleone's code.I have implemented 3 mode of
Animations
i.e Left-to-Right,Right-to-Left & Left+Right .
It also supports Text Color and Marquee only work if text length exceeds the Label width.
Here is my code:
import sys
from PyQt5.QtCore import QEvent, QTimer, pyqtSlot,QRectF
from PyQt5.QtGui import QTextDocument, QPainter, QFontMetrics,QFont,QColor,QAbstractTextDocumentLayout,QPalette
from PyQt5.QtWidgets import QLabel, QApplication
class Document(QTextDocument):
def __init__(self, parent=None):
super().__init__(parent)
def drawContents(self, p, rect=QRectF()):
p.save()
ctx=QAbstractTextDocumentLayout.PaintContext ()
ctx.palette.setColor(QPalette.Text, p.pen().color())
if (rect.isValid()) :
p.setClipRect(rect)
ctx.clip = rect
self.documentLayout().draw(p, ctx)
p.restore()
class Marquee(QLabel):
paused = False
speed = 60
x=0
def __init__(self, parent=None):
super().__init__(parent)
self.document = None
self.timer = QTimer(self)
self.timer.timeout.connect(self.translate)
def setText(self, value,mode="LR"):
f=self.font()
self.fm=QFontMetrics(f)
if self.document is None:
self.document = Document(self)
self.document.setUseDesignMetrics(True)
self.document.setDefaultFont(f)
self.document.setDocumentMargin(0)
if self.timer.isActive() :
self.timer.stop()
if self.fm.width(value) > self.width():
self.nl = int(self.width()/self.fm.horizontalAdvance(" "))
val=' '*self.nl +value+' '*self.nl
self.document.setTextWidth(self.fm.width(val)+22 )
self.document.clear()
self.document.setPlainText(val)
self.setMode(mode)
self.timer.start((1 / 60) * 1000)
else:
self.x=(self.width()/2)-(self.fm.width(value)/2)
self.document.clear()
self.document.setPlainText(value)
self.repaint()
def setMode(self,val):
if val=="RL":
self.x = 0
elif val=="LR" :
self.x =-(self.document.textWidth()-self.fm.width(" "*self.nl)-10)
else:
self.x =-(self.document.textWidth()-self.fm.width(" "*self.nl)-10)
self.fstr=True
self.mode=val
#pyqtSlot()
def translate(self):
if not self.paused:
if self.mode=="RL":
if self.width() - self.x < self.document.textWidth():
self.x -= 1
else:
self.x=0
elif self.mode=="LR" :
if self.x<=0:
self.x+= 1
else:
self.x =-(self.document.textWidth()-self.fm.width(" "*self.nl)-10)
else:
if self.fstr:
if self.x<=0:
self.x+= 1
else:
self.x =0
self.fstr=False
else:
if self.width() - self.x < self.document.textWidth():
self.x -= 1
else:
self.x=-(self.document.textWidth()-self.fm.width(" "*self.nl)-10)
self.fstr=True
self.repaint()
def event(self, event):
if event.type() == QEvent.Enter:
self.paused = True
elif event.type() == QEvent.Leave:
self.paused = False
return super().event(event)
def getColor(self)->QColor:
if self.styleSheet()=='':
return QColor("grey")
else:
style =self.styleSheet().split(";")
color= "".join([s.split(":")[1] for s in style if s.startswith("color")])
return QColor(color)
def paintEvent(self, event):
if self.document:
p = QPainter(self)
self.getColor()
p.setPen(self.getColor())
p.translate(self.x, 0)
self.document.drawContents(p)
return super().paintEvent(event)
if __name__ == '__main__':
app = QApplication(sys.argv)
w = Marquee()
w.setFixedSize(250, 60)
w.setStyleSheet("background-color:black;color:yellow")
f=QFont()
f.setPointSize(20)
f.setBold(True)
f.setItalic(True)
f.setFamily("Courier")
w.setFont(f)
w.setText("consectggftr_conversion_we want",mode="L+R") # or "RL" or "LR"
There is also better version of this Code provided by #eyllanesc Here

Answer 3

There's nothing in Qt that does that by default. You will indeed need to create an animation that changes the text.
You can use QFontMetrics (label.fontMetrics()) to determine if the label text is larger than then QLabel (to know if you need to scroll it or not). You need a way to repaint the QLabel every half second or so to animate the scrolling. The easiest way is probably a QTimer. The easiest method would probably be to subclass QLabel and have it check if it needs to scroll itself and reset the text every half second or so to simulate the scrolling.
If you wanted scrolling to be even smoother (at a sub-character level), you'd have to override the paint method and paint the text yourself translating and clipping it as necessary.