Implementation of visual part of course project

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys

from OpenGL.GL import *
from OpenGL.GLU import *
from PyQt4 import QtGui, QtCore
from PyQt4.QtOpenGL import *

class MyMainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        widget = MyGlWidget(self)
        self.setCentralWidget(widget)

class MyGlWidget(QGLWidget):
    def __init__(self, parent):
        QGLWidget.__init__(self, parent)
        self.setMinimumSize(500, 500)
        self.arrows = []

    def paintGL(self):
        glClearColor(1.0, 1.0, 1.0, 1.0)
        glClear(GL_COLOR_BUFFER_BIT)

        glEnable(GL_LINE_SMOOTH)
        glHint(GL_LINE_SMOOTH_HINT, GL_NICEST)

        glLineWidth(1.2)
        glPointSize(1)

        for arrow in self.arrows:
            arrow.paint()

    def resizeGL(self, w, h):
        if(h == 0):
            h = 1
        glViewport(0, 0, w, h)
        glMatrixMode(GL_PROJECTION)
        glLoadIdentity()
        aspectRatio = float(float(w) / float(h))

        if (w <= h):
            glOrtho(0, 500.0, 0, 500.0/aspectRatio, 1.0, -1.0)
        else:
            glOrtho(0, 500.0*aspectRatio, 0, 500.0, 1.0, -1.0)

        glMatrixMode(GL_MODELVIEW)
        glLoadIdentity()

    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton:
            self.drawing = True
            self.current_arrow = Arrow(self)
            self.current_arrow.x1 = event.pos().x()
            self.current_arrow.y1 = event.pos().y()
            self.current_arrow.x2 = event.pos().x()
            self.current_arrow.y2 = event.pos().y()
            self.arrows.append(self.current_arrow)

    def mouseMoveEvent(self, event):
        if self.drawing == True:
            self.current_arrow.x2 = event.pos().x()
            self.current_arrow.y2 = event.pos().y()
            self.paintGL()

    def mouseReleaseEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton and self.drawing:
            self.current_arrow.x2 = event.pos().x()
            self.current_arrow.y2 = event.pos().y()
            self.paintGL()
            self.drawing = False

class Arrow(object):
    def __init__(self, view):
        self.x1 = 0
        self.y1 = 0
        self.x2 = 0
        self.y2 = 0
        self.view = view

    def paint(self):
        x1 = self.x1
        y1 = self.y1
        x2 = self.x2
        y2 = self.y2

        y1 = self.view.height() - y1
        y2 = self.view.height() - y2

        bezscale = 20
        bezmiddle = abs(x2-x1)/1.5

        glEnable(GL_MAP1_VERTEX_3)
        ctrlpoints=[[x1, y1, 0.01],
            [x1+bezscale, y1, 0.01], [x1+bezmiddle, y1, 0.01],
            [x2-bezmiddle, y2, 0.01], [x2-bezscale, y2, 0.01],
            [x2, y2, 0.01]]

        glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, ctrlpoints)
        glColor3f(0.4, 0.4, 0.4)
        glBegin(GL_LINE_STRIP)
        SEGS=20
        for p in range(0, SEGS+1):
            glEvalCoord1f(float(p)/float(SEGS))
        glEnd()

        arrow_size = 5

        glBegin(GL_POLYGON)
        glVertex2i( x2, y2 )
        glVertex2i( x2-arrow_size, y2-arrow_size )
        glVertex2i( x2-arrow_size, y2+arrow_size )
        glEnd()
        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
        self.view.swapBuffers()

def main(argv):
    import sys
    app = QtGui.QApplication(sys.argv)
    window = MyMainWindow()
    window.show()
    app.exec_()

if __name__ == "__main__":
    main(sys.argv)