2008-05-02
What is pyclutter? Pyclutter is the python binding to the clutter library: a high level OpenGL library for creating animated user interfaces.

OK, so this isn't really a tutorial because I'm not going to go through each line of code and explain what it does. However, there are certain parts of the code that I will give a bit more info about, because I had some problems figuring it out and I'm hoping my experience will help other.

This is not a static "hello world". I know, I broke the rules; but I think this is a good thing. Upon running the script, there will be a "hello" on the screen. Pressing "s" on the keyboard will initiate a switching toggle between "hello" and "world" by animating a change in their opacities. Pressing "q" will quit the app. Check it out
 #!/usr/bin/env python
print "Hello World!"

Ha ha, just kidding.....
#!/usr/bin/env python

import clutter

class clutterTest:
def __init__(self):
#create a clutter stage
self.stage = clutter.Stage()
#set the stage size in x,y pixels
self.stage.set_size(500,200)
#define some clutter colors in rgbo (red,green,blue,opacity)
color_black =clutter.Color(0,0,0,255)
color_green =clutter.Color(0,255,0,255)
color_blue =clutter.Color(0,0,255,255)
#set the clutter stages bg color to our black
self.stage.set_color(color_black)
#we will need to check on the key presses from the user
self.stage.connect('key-press-event', self.parseKeyPress)
#create a clutter label, is there documentation for creating a clutterlabel?
self.label = clutter.Label()
#set the labels font
self.label.set_font_name('Mono 32')
#add some text to the label
self.label.set_text("Hello")
#make the label green
self.label.set_color(color_green )
#put the label in the center of the stage
(label_width, label_height) = self.label.get_size()
label_x = (self.stage.get_width()/2) - label_width/2
label_y = (self.stage.get_height()/2) - label_height/2
self.label.set_position(label_x, label_y)
#make a second label similar to the first label
self.label2 = clutter.Label()
self.label2.set_font_name('Mono 32')
self.label2.set_text("World!")
self.label2.set_color(color_blue )
(label2_width, label2_height) = self.label2.get_size()
label2_x = (self.stage.get_width()/2) - label2_width/2
label2_y = (self.stage.get_height()/2) - label2_height/2
self.label2.set_position(label2_x, label2_y)
#hide the label2
self.label2.set_opacity(0)
#create a timeline for the animations that are going to happen
self.timeline = clutter.Timeline(fps=20,duration=500)
#how will the animation flow? ease in? ease out? or steady?
#ramp_inc_func will make the animation steady
labelalpha = clutter.Alpha(self.timeline, clutter.ramp_inc_func)
#make some opacity behaviours that we will apply to the labels
self.hideBehaviour = clutter.BehaviourOpacity(255,0x00,labelalpha)
self.showBehaviour = clutter.BehaviourOpacity(0x00,255,labelalpha)
#add the items to the stage
self.stage.add(self.label2)
self.stage.add(self.label)
#show all stage items and enter the clutter main loop
self.stage.show_all()
clutter.main()

def parseKeyPress(self,actor, event):
#do stuff when the user presses a key
#it would be awesome if I could find some documentation regarding clutter.keysyms
if event.keyval == clutter.keysyms.q:
#if the user pressed "q" quit the test
clutter.main_quit()
elif event.keyval == clutter.keysyms.s:
#if the user pressed "s" swap the labels
self.swapLabels()


def swapLabels(self):
#which label is at full opacity?, like the highlander, there can be only one
if(self.label.get_opacity()>1 ):
showing = self.label
hidden = self.label2
else:
showing = self.label2
hidden = self.label
#detach all objects from the behaviors
self.hideBehaviour.remove_all()
self.showBehaviour.remove_all()
#apply the behaviors to the labels
self.hideBehaviour.apply(showing)
self.showBehaviour.apply(hidden)
#behaviours do nothing if their timelines are not running
self.timeline.start()



if __name__=="__main__":
test = clutterTest()


Copy the code and drop it into your favorite text editor.
things I got hung up on....
1. Labels:the pyclutter documentation doesn't reference labels. Fortunately, the pyclutter examples that are included with the pyclutter source code, have a sample of a label
2. Alpha: clutter.alpha is a representation of a value based on a clutter.timeline and a function to determine the value at a given time on the time line. The first function that I used was a sine function that would peak at the midway point and then return to the starting point. So my opacity behavior would go from 0 to 255 and then back to 0, when what I really wanted was to go from 0 to 255.
3. behaviourOpacity: When the behavior transitions the opacity from 255 to 0, the ending opacity is 1, or at least is was the last time I checked. Odd.
4. Determining which key is pressed: I don't know enough about python to be able to print out all of the data in the event object that is sent when there is a "key-press-event". I was trying to print the keys from the event objects dict but nothing was working. Luckily, I stumbles upon the clutter.keysyms doohicky but I haven't found all of the documentation for the keysyms yet. For now, I just use clutter.keysyms.[what key am I looking for] to determine if a specific key is pressed.

That's it for now...
Comments
2009-09-23 kelvan:
doesn't work with python-clutter1.0.0
2009-09-23 jezra:
This example was written for clutter 0.6. Fortunately, the python backtraces make it fairly easy to determine what has changed from 0.6 to 1.0. In this case, it is probably the change of the "Label" object to a "Text" object.
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