#!/usr/bin/env python
import gtk
import cairo

def shift(x,sz):
  return  0.5-(x*sz)%1

def lineshift(x1,y1,x2,y2,sz):
  dx1 = shift(x1,sz)
  dy1 = shift(y1,sz)
  dx2 = shift(x2,sz)
  dy2 = shift(y2,sz)
  dx = max(dx1,dx2)
  dy = max(dy1,dy2)
  return dx,dy

class MainWindow(gtk.Window):
  def __init__(self, parent=None):
    gtk.Window.__init__(self)
    try:
      self.set_screen(parent.get_screen())
    except AttributeError:
        self.connect('destroy', lambda *w: gtk.main_quit())
    self.zoom = 1
    self.set_title("pycairo test")
    self.set_default_size(400, 300)
    self.da = gtk.DrawingArea()
    self.da.connect("button_press_event",self.on_button_press)
    self.da.set_events(gtk.gdk.BUTTON_PRESS_MASK)
    self.add(self.da)
    self.da.connect('expose_event', self.expose)
    self.show_all()

  def expose (self,da,event):
    ctx = da.window.cairo_create()
    sz = self.zoom
    ctx.set_line_width(1)

    ## red 'x' starts here
    ctx.save()
    ## coords of the 1st stem
    x1,y1,x2,y2 = 30,10,50,30 
    ctx.set_source_rgb(1,0,0)
    m = cairo.Matrix(self.zoom,0,0,self.zoom,0,0)
    ctx.transform(m)
    ctx.move_to(x1,y1)
    ctx.line_to(x2,y2)
    ctx.stroke()
    ctx.restore()

    ctx.save()
    x1,y1,x2,y2 = 50,10,30,30
    ## coords of the 2nd stem
    ctx.set_source_rgb(1,0,0)
    m = cairo.Matrix(self.zoom,0,0,self.zoom,0,0)
    ctx.transform(m)
    ctx.move_to(x1,y1)
    ctx.line_to(x2,y2)
    ctx.stroke()
    ctx.restore()
    
    ## black '+' starts here
    ctx.save()
    x1,y1,x2,y2 = 10,20,20,20
    ## calculate 0.5 shift
    dx,dy = lineshift(x1,y1,x2,y2,sz)
    m = cairo.Matrix(self.zoom,0,0,self.zoom,dx,dy)
    ctx.transform(m)
    ctx.move_to(x1,y1)
    ctx.line_to(x2,y2)
    ## do not stroke it inside of save()/restore()
    ctx.restore()

    ctx.save()
    x1,y1,x2,y2  = 15,15,15,25
    ## calculate 0.5 shift
    dx,dy = lineshift(x1,y1,x2,y2,sz)
    m = cairo.Matrix(self.zoom,0,0,self.zoom,dx,dy)
    ctx.transform(m)
    ctx.move_to(x1,y1)
    ctx.line_to(x2,y2)
    ## do not stroke it inside of save()/restore()
    ctx.restore()
    ## now stroke both black '+' stems
    ctx.stroke()

  def on_button_press(self,da,event):
    if event.button == 1:
      self.zoom*=1.4
    if event.button == 3:
      self.zoom/=1.4
    ## I'm lazy to send 'expose' signal, so I just hide/show drawing area here
    da.hide()
    da.show()

def main():
  MainWindow()
  gtk.main()

if __name__ == '__main__':
  main()