# -*- coding: cp1251 -*-

from PyQt4 import QtCore, QtGui
import sys
import os

class MainForm(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)

        self.scribbling = False
        self.myPenWidth = 1
        self.myPenColor = QtCore.Qt.blue
        self.lastPoint = QtCore.QPoint()

    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton:
            self.lastPoint = event.pos()
            self.scribbling = True

    def mouseMoveEvent(self, event):
        if (event.buttons() & QtCore.Qt.LeftButton) and self.scribbling:
            self.drawLineTo(event.pos())

    def mouseReleaseEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton and self.scribbling:
            self.drawLineTo(event.pos())
            self.scribbling = False

    def drawLineTo(self, endPoint):
        painter = QtGui.QPainter()
        painter.begin(self)
        painter.setPen(QtGui.QPen(self.myPenColor, self.myPenWidth, QtCore.Qt.SolidLine, QtCore.Qt.RoundCap, QtCore.Qt.RoundJoin))
        painter.drawLine(self.lastPoint, endPoint)
        painter.end()

        rad = self.myPenWidth / 2 + 2
        self.update(QtCore.QRect(self.lastPoint, endPoint).normalized().adjusted(-rad, -rad, +rad, +rad))
        self.lastPoint = QtCore.QPoint(endPoint)

class App(QtGui.QApplication):
    def __init__(self, *args):
        QtGui.QApplication.__init__(self, *args)
        self.ui = MainForm(None)
        self.ui.show()

if __name__ == "__main__":
    app = App(sys.argv)
    app.exec_()

QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setPen: Painter not active
QPainter::end: Painter not active, aborted

    def drawLineTo(self, endPoint):
        painter = QtGui.QPainter()
        painter.begin(QtGui.QApplication.desktop().screen())
        painter.setPen(QtGui.QPen(self.myPenColor, self.myPenWidth, QtCore.Qt.SolidLine, QtCore.Qt.RoundCap, QtCore.Qt.RoundJoin))
        painter.drawLine(self.lastPoint, endPoint)
        painter.end()

    def drawLineTo(self, endPoint):
        painter = QtGui.QPainter()
        painter.begin(QtGui.QApplication.desktop().screen(), True)
        painter.setPen(QtGui.QPen(self.myPenColor, self.myPenWidth, QtCore.Qt.SolidLine, QtCore.Qt.RoundCap, QtCore.Qt.RoundJoin))
        painter.drawLine(self.lastPoint, endPoint)
        painter.end()

#!/usr/bin/env python2.6
# coding: utf-8
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Widget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setWindowFlags(Qt.WindowStaysOnTopHint | Qt.FramelessWindowHint)
        self.setAttribute(Qt.WA_TranslucentBackground)

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.setBrush(Qt.blue)
        painter.drawEllipse(0, 0, 100, 100)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = Widget()
    w.resize(105, 105)
    w.show()
    sys.exit(app.exec_())

# -*- coding: cp1251 -*-
from pythoncom import PumpMessages
from pyHook import HookManager
import win32gui
from win32con import PS_SOLID
import win32con
import win32api

global scribbling, lastPoint, controlDown

def OnKeyboardEvent(event):
    global scribbling, lastPoint, controlDown
    if event.GetMessageName() == 'key down' and event.Key in ['Lcontrol', 'Rcontrol']:
        controlDown = True
    elif event.GetMessageName() == 'key up' and event.Key in ['Lcontrol', 'Rcontrol']:
        controlDown = False
    return True # False делать опасно! Скрипт НЕ передаст сигнал системе
    
def OnMouseDown(event):
    global scribbling, lastPoint
    if event.GetMessageName() == 'mouse left down' and controlDown:
        lastPoint = event.Position
        scribbling = True
        return False
    return True
def OnMouseUp(event):
    global scribbling
    if event.GetMessageName() == 'mouse left up' and scribbling:
        drawLineTo(event.Position)
        scribbling = False
    return True
def OnMouseMove(event):
    global scribbling
    if scribbling:
        drawLineTo(event.Position)
        # return False
    return True
def drawLineTo(endPoint):
    global lastPoint
    x1,y1 = lastPoint
    x2,y2 = endPoint
    lastPoint = endPoint
    clRed = 0x0000ED # Цвет для рисования
    # Получаем контекст экрана рабочего стола
    screenDC = win32gui.GetDC(None)
    # Создаем новые карандаш и кисть
    penHandle = win32gui.CreatePen(PS_SOLID, 1, clRed)
    oldPenHandle = win32gui.SelectObject(screenDC, penHandle)
    
    brushHandle = win32gui.CreateSolidBrush(clRed)
    oldBrushHandle = win32gui.SelectObject(screenDC, brushHandle)
    # Рисуем на рабочем столе
    """ Рисование прямоугольника
    left = 100
    top = 100
    width = 200
    height = 300
    win32gui.Rectangle(screenDC, left, top, left+width, top + height)
    # """
    win32gui.MoveToEx(screenDC,x1, y1)
    win32gui.LineTo(screenDC,x2,y2)
    # Освобождаем память от карандаша, кисти и указателя на рабочий стол
    win32gui.SelectObject(screenDC, oldBrushHandle)
    win32gui.DeleteObject(brushHandle)

    win32gui.SelectObject(screenDC, oldPenHandle)
    win32gui.DeleteObject(penHandle)

    win32gui.ReleaseDC(0, screenDC)

scribbling = False
lastPoint = None
controlDown = False

hookm = HookManager()
# Определям функцию на перехват
hookm.MouseLeftDown = OnMouseDown
hookm.MouseLeftUp = OnMouseUp
hookm.MouseMove = OnMouseMove
# Определям функцию на перехват клавиши
hookm.KeyDown = OnKeyboardEvent
hookm.KeyUp = OnKeyboardEvent
# Указываем перехватывать события
hookm.HookMouse()
hookm.HookKeyboard()
# Запускаем все действо
PumpMessages()

hCurs1 = win32api.LoadCursor(0, win32con.IDC_CROSS)
win32api.SetCursor(hCurs1)