a soft-edged disc with alpha blending - the outer edge is fully transparent, while the center of the disc is opaque

alphawheel.py

import time, math
from pyglet.gl import *

window = pyglet.window.Window()

class Square:
    def __init__(self, color):
        self.color = color
        self.vlist = pyglet.graphics.vertex_list(4, ('v2f', [-128,-128, 128,-128, -128,128, 128,128]))
    def draw(self):
        glColor3f(self.color[0],self.color[1],self.color[2])
        self.vlist.draw(GL_TRIANGLE_STRIP)
    def update(self,dt):
        pass

class AlphaWheel:
    def __init__(self, moveradius, color):
        self.moveradius = moveradius
        self.xpos = 0
        self.ypos = 0
        verts = [0,0]
        colors = [color[0], color[1], color[2], 1]
        for angle in range(0,361, 10):
            verts += [math.sin(angle*math.pi/180.0)*128, math.cos(angle*math.pi/180.0)*128]
            colors += [color[0], color[1], color[2], 0]
        self.vlist = pyglet.graphics.vertex_list(len(verts)/2, ('v2f', verts), ('c4f', colors))
    def draw(self):
#        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)
        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
        glPushMatrix()
        glTranslatef(self.xpos, self.ypos, 0)
        self.vlist.draw(GL_TRIANGLE_FAN)
        glPopMatrix()
        glDisable(GL_BLEND)
    def update(self,dt):
        self.xpos = self.moveradius * math.sin(time.time())
        self.ypos = self.moveradius * math.cos(time.time())


objects = [ Square([1,1,1]), AlphaWheel(128, [1,0,0]) ]


@window.event
def on_draw():
    glClearColor(0, 0.3, 0.5, 0)
    glClear(GL_COLOR_BUFFER_BIT)
    
    glLoadIdentity()
    glTranslatef(320, 240, 0)

    for o in objects:
        o.draw()
    

def update(dt):
    for o in objects:
        o.update(dt)


pyglet.clock.schedule_interval(update,1/60.0)
pyglet.app.run()