Handling events using pycairo

Mr SZ sk8in_zombi at yahoo.com.au
Tue Jul 15 21:17:45 CEST 2008


Hi,



I'm trying to create a rectangle when the user presses or releases the
mouse over a cairo object.I'm using the eventBox to capture the mouse
events.

Now the problem is the shapes is beng drawn when I call it from the
expose_event event handler and nothing happens when I call the same
from the mouse release event handler.



Here is my code :



#!/usr/bin/env python



import sys

import cairo

import gtk





start = None #Starting co-ords

stop = None #Ending co-ords

box = None  #Tuple of co-ords for drawing rect

ctx = None #Cairo Widget

def button_press(widget, event, surface):

    global start

    start = (int(event.x),int(event.y))

def motion_notify(widget, event, surface):

    pass

def button_release(widget, event, surface):

    global stop,ctx

    ctx = None

    ctx = widget.window.cairo_create()

    ctx.set_source_surface(surface, 0,0)

    ctx.paint()

    print ctx

    stop =  (int(event.x),int(event.y))

    box = (start[0],start[1])

    draw_dotrect(ctx,box)

    print "Released" + str(box)



def draw_dotrect(ctx,box):

    ctx.set_source_rgba(0, 0, 0,0.5)

    ctx.save()

    ctx.new_path()

    ctx.translate(3*20, 0)

    square(ctx,box)

    ctx.fill()

    ctx.restore()

    ctx.set_line_width(20 / 16)

    ctx.set_tolerance(0.1)

    ctx.set_line_join(cairo.LINE_JOIN_MITER)

    ctx.set_dash([20/2.0, 20/2.0], 8)

    ctx.save()

    ctx.new_path()

    ctx.set_source_rgb(0,0 ,0 )

    ctx.translate(3*20, 0)

    square(ctx,box)

    ctx.stroke_preserve()

    ctx.restore()

    

def expose_event(widget, event, surface):

    global ctx

    ctx = widget.window.cairo_create()

    ctx.set_source_surface(surface, 0,0)

    ctx.paint()

    

    #draw_dotrect(ctx,(20,20)) # If called from here,it works

    

    

def square(ctx,box):

    ctx.move_to(0, 0)

    ctx.rel_line_to(2*50, 0)

    ctx.rel_line_to(0, 2*50)

    ctx.rel_line_to(-2*50, 0)

    ctx.close_path()

    

    if len(sys.argv) != 2:

        raise SystemExit('usage: png_view.py png_file')



filename = sys.argv[1]



surface = cairo.ImageSurface.create_from_png(filename)

Width  = surface.get_width()

Height = surface.get_height()



win = gtk.Window()

win.connect('destroy', gtk.main_quit)



event_box = gtk.EventBox()

win.add(event_box)



drawingarea = gtk.DrawingArea()

event_box.add(drawingarea)



drawingarea.connect('expose_event', expose_event, surface)

event_box.connect('button_press_event',button_press,surface)

event_box.connect('button_release_event',button_release,surface)

event_box.connect('motion_notify_event',motion_notify,surface)



drawingarea.set_size_request(Width,Height)



win.show_all()

gtk.main()



It doesn't throw me any error.I hardcoded the box to simplify things
.    I also create a new ctx in the release event handler else it
throws an error:CAIRO_STATUS_SURFACE_FINISHED




Any ideas why ?

" life isn't heavy enough,it flies away and floats far above action"


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