Drawing In Pygobject (python3)

I'm trying to write simple graphic editor using PyGObject and python 3. I need to draw lines with different color and width using mouse. I found many examples like this but nothing

Solution 1:

You need to use a Double Buffer technique:

http://en.wikipedia.org/wiki/Multiple_buffering#Double_buffering_in_computer_graphics

That is you have an image, and you draw over that image: that image is the "behind the scenes" buffer. You can have a lot of methods that draw something to that image. Then, on the callback that responds to 'draw' signal, that is, the method that actually draws something to the graphics memory you just throw your "behind the scenes" image.

Theory in code (test.py):

import cairo
from gi.repository import Gtk
from os.path import abspath, dirname, join

WHERE_AM_I = abspath(dirname(__file__))

classMyApp(object):
    """Double buffer in PyGObject with cairo"""def__init__(self):
        # Build GUI
        self.builder = Gtk.Builder()
        self.glade_file = join(WHERE_AM_I, 'test.glade')
        self.builder.add_from_file(self.glade_file)

        # Get objects
        go = self.builder.get_object
        self.window = go('window')

        # Create buffer
        self.double_buffer = None# Connect signals
        self.builder.connect_signals(self)

        # Everything is ready
        self.window.show()

    defdraw_something(self):
        """Draw something into the buffer"""
        db = self.double_buffer
        if db isnotNone:
            # Create cairo context with double buffer as is DESTINATION
            cc = cairo.Context(db)

            # Scale to device coordenates
            cc.scale(db.get_width(), db.get_height())

            # Draw a white background
            cc.set_source_rgb(1, 1, 1)

            # Draw something, in this case a matrix
            rows = 10
            columns = 10
            cell_size = 1.0 / rows
            line_width = 1.0
            line_width, notused = cc.device_to_user(line_width, 0.0)

            for i inrange(rows):
                for j inrange(columns):
                    cc.rectangle(j * cell_size, i * cell_size, cell_size, cell_size)
                    cc.set_line_width(line_width)
                    cc.set_source_rgb(0, 0, 0)
                    cc.stroke()

            # Flush drawing actions
            db.flush()
            
        else:
            print('Invalid double buffer')

    defmain_quit(self, widget):
        """Quit Gtk"""
        Gtk.main_quit()

    defon_draw(self, widget, cr):
        """Throw double buffer into widget drawable"""if self.double_buffer isnotNone:
            cr.set_source_surface(self.double_buffer, 0.0, 0.0)
            cr.paint()
        else:
            print('Invalid double buffer')

        returnFalsedefon_configure(self, widget, event, data=None):
        """Configure the double buffer based on size of the widget"""# Destroy previous bufferif self.double_buffer isnotNone:
            self.double_buffer.finish()
            self.double_buffer = None# Create a new buffer
        self.double_buffer = cairo.ImageSurface(\
                cairo.FORMAT_ARGB32,
                widget.get_allocated_width(),
                widget.get_allocated_height()
            )

        # Initialize the buffer
        self.draw_something()

        returnFalseif __name__ == '__main__':
    gui = MyApp()
    Gtk.main()

Glade file (test.glade):

<?xml version="1.0" encoding="UTF-8"?><interface><!-- interface-requires gtk+ 3.0 --><objectclass="GtkWindow"id="window"><propertyname="can_focus">False</property><propertyname="window_position">center-always</property><propertyname="default_width">800</property><propertyname="default_height">600</property><signalname="destroy"handler="main_quit"swapped="no"/><child><objectclass="GtkDrawingArea"id="drawingarea1"><propertyname="visible">True</property><propertyname="can_focus">False</property><signalname="draw"handler="on_draw"swapped="no"/><signalname="configure-event"handler="on_configure"swapped="no"/></object></child></object></interface>

Dependencies:

Python 2:

sudo apt-get install python-cairo

Python 3:

sudo apt-get install python3-gi-cairo

Now execute with:

python test.py

or

python3 test.py

What it looks like:

All the documentation for cairo can be found in http://cairographics.org/documentation/pycairo/3/reference/index.html

Kind regards