'Draw black edges around the block that is currently under the
crosshairs.'

def draw_focused_block(self):

    vector = self.get_sight_vector()
    block = self.model.hit_test(self.position, vector)[0]
    if block:
        (x, y, z) = block
        vertex_data = cube_vertices(x, y, z, 0.51)
        glColor3d(0, 0, 0)
        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)
        pyglet.graphics.draw(24, GL_QUADS, ('v3f/static', vertex_data))
        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL)
