Computer graphics 2

import sys
from ui_mainform import Ui_MainWindow
from PySide.QtCore import *
from PySide.QtGui import *

class Point(object):
    def __init__(self, x, y):
        self.x, self.y = x, y

    def transform(self, k, height):
        return Point(self.x * k, (height - self.y) * k)

class LineFunction(object):
    def __init__(self, pointFrom, pointTo):
        self.pointFrom = pointFrom
        self.pointTo = pointTo
        self.ld = min(abs(pointFrom.x - pointTo.x), abs(pointFrom.y - pointTo.y))
        self.gd = max(abs(pointFrom.x - pointTo.x), abs(pointFrom.y - pointTo.y))
        self.value = self.gd >> 1
        self.d = self.gd - self.ld
        self.step = 0

    def calc_next(self):
        if self.value < 0: self.value += self.d
        else: self.value -= self.ld
        self.step += 1

    def __str__(self):
        s = ''
        if self.step > 0:
            if self.value < 0: s = 'it\'s less then 0; /'
            else: s = 'it\'s >= 0; -'
        return '<font color=blue>Step {0:00}:</font> f({0:0}) = {1} <font color=red>{2}</font>'\
            .format(self.step, self.value, s)

class Form(QMainWindow, Ui_MainWindow):
    def __init__(self):
        super(Form, self).__init__()
        self.setupUi(self)
        self.connect_actions()

    def setupUi(self, MainWindow):
        super(Form, self).setupUi(MainWindow)
        self.scene = QGraphicsScene()
        self.graphicsView.setScene(self.scene)
        self.k = 40

    def connect_actions(self):
        self.pushButtonDraw.clicked.connect(self.draw)
        self.pushButtonClear.clicked.connect(self.clear)

    def draw(self):
        pointFrom = Point(self.spinBoxFromX.value(), self.spinBoxFromY.value())
        pointTo = Point(self.spinBoxToX.value(), self.spinBoxToY.value())
        width = self.spinBoxWidth.value()
        height = self.spinBoxHeight.value()

        self.textBrowserTrace.append('<font color=green><b>Point from: ({0}; {1}), point to: ({2}; {3}).</b></font>'\
            .format(pointFrom.x, pointFrom.y, pointTo.x, pointTo.y))
        self.drawGrid(width, height)
        self.drawLine(pointFrom, pointTo, width, height)
        self.drawPoints(pointFrom, pointTo, width, height)

        self.tabWidget.setCurrentWidget(self.tab_2)

    def drawGrid(self, width, height):
        p = QPen()
        p.setWidth(1)
        p.setBrush(Qt.black)

        self.scene.setSceneRect(0, 0, width * self.k, height * self.k)

        for i in range(0, width + 1):
            self.scene.addLine(i * self.k, 0, i * self.k, height * self.k, p)

        for i in range(0, height + 1):
            self.scene.addLine(0, i * self.k, width * self.k, i * self.k, p)

    def drawLine(self, pointFrom, pointTo, width, height):
        p = QPen()
        p.setWidth(3)
        p.setBrush(Qt.black)
        p.setCapStyle(Qt.RoundCap)

        f = pointFrom.transform(self.k, height)
        t = pointTo.transform(self.k, height)
        self.scene.addLine(f.x, f.y, t.x, t.y, p)

    def drawPoints(self, pointFrom, pointTo, width, height):
        if pointFrom.x >= pointTo.x and pointFrom.y < pointTo.y or \
            pointFrom.x > pointTo.x and pointFrom.y >= pointTo.y:
            tmp, pointFrom = pointFrom, pointTo
            pointTo = tmp

        line = LineFunction(pointFrom, pointTo)
        self.textBrowserTrace.append('<b>Lower:</b> {0}; <b>greater:</b> {1}; <b>delta:</b> {2}.'\
            .format(line.ld, line.gd, line.d))
        self.textBrowserTrace.append(str(line))

        incx, incy = None, None
        if pointFrom.y <= pointTo.y:
            if abs(pointFrom.x - pointTo.x) > abs(pointFrom.y - pointTo.y):
                incx = lambda value: 1
                incy = lambda value: 1 if value < 0 else 0
            else:
                incx = lambda value: 1 if value < 0 else 0
                incy = lambda value: 1
        else:
            if abs(pointFrom.x - pointTo.x) > abs(pointFrom.y - pointTo.y):
                incx = lambda value: 1
                incy = lambda value: -1 if value < 0 else 0
            else:
                incx = lambda value: 1 if value < 0 else 0
                incy = lambda value: -1

        self.__drawPoint(pointFrom.transform(self.k, height))
        for i in range(0, line.gd):
            line.calc_next()
            pointFrom.x += incx(line.value)
            pointFrom.y += incy(line.value)
            self.__drawPoint(pointFrom.transform(self.k, height))
            self.textBrowserTrace.append(str(line))

    def __drawPoint(self, point):
        p = QPen()
        p.setWidth(5)
        p.setBrush(Qt.red)
        p.setCapStyle(Qt.RoundCap)

        print point.x, point.y
        self.scene.addLine(point.x, point.y, point.x + 1, point.y, p)

    def clear(self):
        self.scene.clear()

def main(argv):
    app = QApplication(argv)
    form = Form()
    form.show()
    sys.exit(app.exec_())

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