Fading out a stimulus in Expyriment

fade_out_stim.py

import expyriment, os, pygame, time
from expyriment import design, control, stimuli, io
from expyriment.misc import constants


#expyriment.control.defaults.open_gl = 0
control.set_develop_mode(True)

exp = expyriment.control.initialize()

stim = stimuli.TextLine("A", text_colour=[255,255,255], text_size=100)
stim.preload(True)    
    
bgcanvas_stimlist = []
for x in range(255): # prepare background stimulus with a certain transparency        
    c = stimuli.Canvas(stim.surface_size)
    c._set_surface(c._get_surface().convert())
    c._get_surface().set_alpha(x)
    if expyriment.control.defaults.open_gl:
        c2 = stimuli.Canvas(stim.surface_size)
        c.plot(c2)
        c = c2
    c.preload(True)
    bgcanvas_stimlist.append(c)
   
for x in range(255):    
    stim.present(update=False)
    bgcanvas_stimlist[x].present(clear=False)     # 
    exp.clock.wait(10)
expyriment.control.end()