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How to make the edge of rotating wedge look smoothly

I am a new psychopyer. Following the demo code, I made a rotating wedge. However, the edge seems to flicker always. How to deal with this problem? Here is the code:

from psychopy import visual, core, event

win = visual.Window([800, 800])

wedge = visual.RadialStim(
    win=win,
    tex='sqrXsqr',
    color=-1,
    size=1,
    visibleWedge=[0,360],
    radialCycles=4,
    angularCycles=8,
    interpolate=True,
    autoLog=False
)
clock = core.Clock()
rotationRate = 0.1
t = clock.getTime()
while not event.getKeys():
    t = clock.getTime()
    wedge.ori = t * rotationRate * 360.0
    wedge.draw()
    win.flip()

win.close()
core.quit()