Innovative Interfaces with Clutter
Listing 3. Clutter Rotating a Video
import clutter import gst from clutter import cluttergst class HelloWorld: def __init__ (self): self.stage = clutter.Stage() self.stage.set_color(clutter.color_parse('Black')) self.stage.set_size(500, 400) self.stage.set_title('Clutter 3-D Video Player') # Setup video. video_tex = cluttergst.VideoTexture() self.pipeline = gst.Pipeline("mypipe") playbin = video_tex.get_playbin() movfile = "file:///home/user/Videos/Video.mov" playbin.set_property('uri', movfile) self.pipeline.add(playbin) video_tex.set_position(90,80) self.stage.add(video_tex) self.pipeline.set_state(gst.STATE_PLAYING) # Create timeline that lasts for 100 frames # at ten frames per second. timeline = clutter.Timeline(100, 10) # Set timeline to loop forever. timeline.set_loop(True) # Create an alpha. alpha = clutter.Alpha(timeline, clutter.smoothstep_dec_func) # Set up rotation. Rotation = clutter.BehaviourRotate( axis=clutter.Y_AXIS, direction=clutter.ROTATE_CW, angle_start=0, angle_end=360, alpha=alpha) Rotation.set_center(160, 160, 0) Rotation.apply(video_tex) # Start it all up. timeline.start() self.stage.show_all() clutter.main() # Run program. main = HelloWorld()
The Alpha Functions
At first, especially to those who've forgotten their Calculus and Algebra, the alpha functions may seem unpredictable or confusing. There is a large list of the number of available functions: exp_dec_func, exp_inc_func, ramp_dec_func, ramp_func, ramp_inc_func, sine_dec_func, sine_func, sine_half_func, sine_inc_func, smoothstep_dec_func, smoothstep_inc_func and square_func. Here's a brief explanation of each type:
Exponential functions: depending on whether you're using a decaying function or an increasing function, exponential functions make the animation speed up or slow down at an exponential rate.
Ramp functions: ramp functions animate at a constant speed. However, the full ramp function animates at both a negative and a positive constant speed by switching directions.
Sine functions: sine functions make the animation reverse. Like the graph of a sine function, the animation would speed up, slow down, change directions, speed up in the reverse direction, and then slow down again.
Smooth step functions: the smooth step function works logistically. It starts slowly, then quickly increases and finally slows down toward the end of the animation.
Square functions: square functions follow a step pattern, which results in quick changes between two constant animation speeds.
Hopefully, you've learned a good deal about how Clutter works, and you can start developing and programming using the Clutter API. Using just the features you've seen here, you'll be able to create any interface that uses text, buttons, images and video with Clutter. Of course, after learning the basics, the more advanced UI elements will become easier to understand and work with.
In the future, the Clutter developers will continue to improve and update the API, and many new improvements are expected in the Clutter 1.0 release. You can learn more about the Clutter development process from the Web site (see Resources). Clutter is going to power many innovative open-source applications in the future.
Alex Crits-Christoph has been working with Linux for some time now. He enjoys developing and designing open-source graphical user interfaces.
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