Pyglet hello world example doesn't show label until a key is pressed - python-3.x

Question

import pyglet
window = pyglet.window.Window()
label = pyglet.text.Label("Hello World!",
font_name="Times New Roman",
color=(255,255,255,255),
font_size=36,
x=window.width//2, y=window.height//2,
anchor_x="center", anchor_y="center")
#window.event
def on_draw():
window.clear()
label.draw()
pyglet.app.run()
This code is taken from the pyglet tutorial at https://pyglet.readthedocs.io/en/pyglet-1.2-maintenance/programming_guide/quickstart.html but when run it doesn't draw the label until any key is pressed. I added the color as I thought the text may have defaulted to black.
Am I missing something really obvious as to why this behaviour is happening?
OK, having had my memory jogged by the comments, I installed the MS Fonts and it now works in python 2.x but I still need to press a key to see the text in python 3. Maybe the font thing is a red-herring and there is some incompatibility with python 3.

Answer 1

As mentioned in the comments.
Most examples found on the internet (even most guides) assume a Windows platform.
If there's a font= declaration with a Windows font but you're running Linux, make sure you got the proper fonts installed or revert to a font you've got installed.
$ fc-list
Also not declaring a font will work too:
label = pyglet.text.Label("Hello World!",
color=(255,255,255,255),
font_size=36,
x=window.width//2, y=window.height//2,
anchor_x="center", anchor_y="center")
Because Pyglet will default to sans-serif:
If you do not particularly care which font is used, and just need to display some readable text, you can specify None as the family name, which will load a default sans-serif font (Helvetica on Mac OS X, Arial on Windows XP)
Your issue is probably that you don't manually update the screen after you drew something. Normally when you press a key, it forces a window.flip(), which basically means update the screen content.
window.clear() also triggers this behavior, but x.draw() does not. Why? Well the thing that takes time in computer graphics is not really the calculations, it's the updating them to the screen that takes time.. There for .draw() doesn't update the screen, it just puts the stuff in the graphical buffer ("page"), you decide when to flip the page and show the new buffer on the screen.
Try this out:
#window.event
def on_draw():
window.clear()
label.draw()
window.flip()
This might be a overkill solution, but it will probably solve the problem.
This overrides the default loop of pyglet and the default draw behavior, it's also one of the classes i use the most in my pyglet projects since it gives me the option to create my own framework.
import pyglet
class Window(pyglet.window.Window):
def __init__(self):
super(Window, self).__init__(vsync = False)
self.sprites = {}
self.sprites['testlabel'] = label = pyglet.text.Label("Hello World!",
color=(255,255,255,255),
font_size=36,
x=self.width//2, y=self.height//2, #self here, being pyglet.window.Window that we've inherited and instanciated with super().
anchor_x="center", anchor_y="center")
self.alive = 1
def on_draw(self):
self.render()
def render(self):
self.clear()
for sprite_name, sprite_obj in self.sprites.items():
sprite_obj.draw()
self.flip()
def on_close(self):
self.alive = 0
def run(self):
while self.alive:
self.render()
# This is very important, this queries (and empties)
# the pyglet event queue, if this queue isn't cleared
# pyglet will hang because it can't input more events,
# and a full buffer is a bad buffer, so we **NEED** this!
event = self.dispatch_events()
win = Window()
win.run()
It's extremely basic, but you can add more sprites, objects and render them in def render(self):.