Modify [quad.py](https://github.com/vispy/vispy/blob/master/examples/tutorial/gl/quad.py) to make it work offscreen with EGL background as in [offscreen.py](https://github.com/vispy/vispy/blob/master/examples/demo/gloo/offscreen.py).

quad_offscreen.py

# -*- coding: utf-8 -*-
# -----------------------------------------------------------------------------
# Copyright (c) Vispy Development Team. All Rights Reserved.
# Distributed under the (new) BSD License. See LICENSE.txt for more info.
# -----------------------------------------------------------------------------
# Author: Nicolas P .Rougier
# Date:   04/03/2014
# -----------------------------------------------------------------------------
import numpy as np
import time

from vispy import app
from vispy.gloo import gl
from vispy.gloo.util import _screenshot

vertex_code = """
    uniform float scale;
    attribute vec4 color;
    attribute vec2 position;
    varying vec4 v_color;
    void main()
    {
        gl_Position = vec4(scale*position, 0.0, 1.0);
        v_color = color;
    } """

fragment_code = """
    varying vec4 v_color;
    void main()
    {
        gl_FragColor = v_color;
    } """


class Canvas(app.Canvas):
    def __init__(self):
        app.Canvas.__init__(self, show=False, size=(512, 512), title='Quad (GL)',
                            keys='interactive')

    def on_initialize(self, event):
        # Build data
        self.data = np.zeros(4, [("position", np.float32, 2),
                                 ("color",    np.float32, 4)])
        self.data['color'] = [(1, 0, 0, 1), (0, 1, 0, 1),
                              (0, 0, 1, 1), (1, 1, 0, 1)]
        self.data['position'] = [(-1, -1), (-1, +1),
                                 (+1, -1), (+1, +1)]

        # Build & activate program

        # Request a program and shader slots from GPU
        program = gl.glCreateProgram()
        vertex = gl.glCreateShader(gl.GL_VERTEX_SHADER)
        fragment = gl.glCreateShader(gl.GL_FRAGMENT_SHADER)

        # Set shaders source
        gl.glShaderSource(vertex, vertex_code)
        gl.glShaderSource(fragment, fragment_code)

        # Compile shaders
        gl.glCompileShader(vertex)
        gl.glCompileShader(fragment)

        # Attach shader objects to the program
        gl.glAttachShader(program, vertex)
        gl.glAttachShader(program, fragment)

        # Build program
        gl.glLinkProgram(program)

        # Get rid of shaders (no more needed)
        gl.glDetachShader(program, vertex)
        gl.glDetachShader(program, fragment)

        # Make program the default program
        gl.glUseProgram(program)

        # Build buffer

        # Request a buffer slot from GPU
        self._fbo = gl.glCreateBuffer()

        # Make this buffer the default one
        gl.glBindBuffer(gl.GL_ARRAY_BUFFER, self._fbo)

        # Upload data
        gl.glBufferData(gl.GL_ARRAY_BUFFER, self.data, gl.GL_DYNAMIC_DRAW)

        # Bind attributes
        stride = self.data.strides[0]
        offset = 0
        loc = gl.glGetAttribLocation(program, "position")
        gl.glEnableVertexAttribArray(loc)
        gl.glBindBuffer(gl.GL_ARRAY_BUFFER, self._fbo)
        gl.glVertexAttribPointer(loc, 3, gl.GL_FLOAT, False, stride, offset)

        offset = self.data.dtype["position"].itemsize
        loc = gl.glGetAttribLocation(program, "color")
        gl.glEnableVertexAttribArray(loc)
        gl.glBindBuffer(gl.GL_ARRAY_BUFFER, self._fbo)
        gl.glVertexAttribPointer(loc, 4, gl.GL_FLOAT, False, stride, offset)

        # Bind uniforms
        # --------------------------------------
        loc = gl.glGetUniformLocation(program, "scale")
        gl.glUniform1f(loc, 1.0)

        # We manually draw the hidden canvas.
        self.update()


    def on_draw(self, event):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)
        gl.glDrawArrays(gl.GL_TRIANGLE_STRIP, 0, 4)
        self.im = _screenshot((0, 0, self.size[0], self.size[1]))

        # Immediately exit the application.
        app.quit()

    def on_resize(self, event):
        gl.glViewport(0, 0, *event.physical_size)

if __name__ == '__main__':
    start = time.time()
    c = Canvas()
    size = c.size
    app.run()

    # The rendering is done, we get the rendering output (4D NumPy array)
    render = c.im
    print('Finished in %.1fms.' % ( time.time() - start))

    # Now, we display this image with matplotlib to check.
    import matplotlib.pyplot as plt
    plt.figure(figsize=(size[0]/100., size[1]/100.), dpi=100)
    plt.imshow(render, interpolation='none')
    plt.savefig("quad.png")