How do I render *parts* of a svg file?

Question

I want to render parts of a svg file by name but for the life of me I cannot figure out how to do so (using python + gtk).

Here's the svg file in question: http://david.bellot.free.fr/svg-cards/files/SVG-cards-2.0.1.tar.gz (Update: this file no longer exists, but you can track it down at http://svg-cards.sourceforge.net/)

On his site, David, says:

You can draw a card either by rendering the file onto a pixmap and clipping each card manually or by using the card's name through a DOM interface. All cards are embedded into a SVG group.

I don't know what he means by a DOM interface. I have done some searching and the best result I found that seems to fit what I want to do is:

QSvgRenderer *renderer = new QSvgRenderer(QLatin1String("SvgCardDeck.svg"));
QGraphicsSvgItem *black = new QGraphicsSvgItem();
QGraphicsSvgItem *red   = new QGraphicsSvgItem();

black->setSharedRenderer(renderer);
black->setElementId(QLatin1String("black_joker"));

red->setSharedRenderer(renderer);
red->setElementId(QLatin1String("red_joker"));

Notice however that it is for Qt and is not even written in python.

This is what I have so far:

#!/usr/bin/env python

from __future__ import absolute_import

import cairo
import gtk
import rsvg

from xml import xpath
from xml.dom import minidom

window = gtk.Window()
window.set_title("Foo")
window.set_size_request(256, 256)
window.set_property("resizable", False)
window.set_position(gtk.WIN_POS_CENTER)
window.connect("destroy", gtk.main_quit)
window.show()

document = minidom.parse("cards.svg")
element = xpath.Evaluate("//*[@id='1_club']", document)[0]
xml = element.toxml()

svg = rsvg.Handle()
svg.write(xml)

pixbuf = svg.get_pixbuf()

image = gtk.Image()
image.set_from_pixbuf(pixbuf)
image.show()

window.add(image)

gtk.main()

It doesn't work, of course.

What am I missing?

Gallic

Answer 1

The GTK library for rendering SVG is called RSVG. It has python bindings, but they are undocumented, and they don't wrap the rsvg_handle_get_pixbuf_sub() and rsvg_handle_render_cairo_sub() functions which you would normally use for that purpose in C. Here's what you have to do as far as I can tell. You extract the XML node as Adam Crossland suggested. To render it, you have to do something like this:

import gtk
import rsvg
handle = rsvg.Handle()
handle.write(buffer=xml_data) 
# xml_data is the XML string for the object you want
image = gtk.Image()
image.set_from_pixbuf(handle.get_pixbuf())

That's if you want it in a gtk.Image, otherwise do something else with the pixbuf. You can also render it to a Cairo context with handle.render_cairo(cr) where cr is your Cairo context.

EDIT:

Sorry, I didn't read the python bindings closely enough at first. The _sub() functions are implemented using the id= argument, so your program can boil down to this:

#!/usr/bin/env python

import gtk
import rsvg

window = gtk.Window()
window.set_title("Foo")
window.connect("destroy", gtk.main_quit)
window.show()

svg = rsvg.Handle(file='cards.svg')
pixbuf = svg.get_pixbuf(id='#3_diamond')

image = gtk.Image()
image.set_from_pixbuf(pixbuf)
image.show()

window.add(image)

gtk.main()

I tested this and it works. However, the window is the size of the entire SVG canvas, and is clipped to the screen size (which is why I rendered the 3 of diamonds instead of the ace of clubs which is up in the corner.) So you'll still have to find some way to crop the pixbuf around the card that you want, but that shouldn't be too hard.

Supermundane

I actually tried this way too and couldn't figure out why it was doing what it was doing (hence me attempting other solutions to see if I'd get a similar result). Despite the window size being the size of the entire SVG canvas, this solution answers my question (while, of course, raising another question). :) – Gallic

This was super-helpful, though more help would have been useful. To render part of an SVG image you can use handle.render_cairo(cr=c, id="#layer_5") where "c" is a cairo context. The part that wasn't at all obvious to me is that the "#" at the beginning of the id is required. My SVG has ids like 'id="layer_1" ' and I can render individual layers with render_cairo(cr=c, id="#layer_1") – Deloris

Answer 2

Here's my answer to the cropping blank space problem. It's a rough hack but it worked great. This would also serve as a good starting point to get cards for anyone making a card game in python.

import gtk
import rsvg
svg = rsvg.Handle(file="/usr/share/gnome-games-common/cards/gnomangelo_bitmap.svg")
w, h = 202.5, 315
card_names = map(str, range(1,11)) + ["jack", "queen", "king"]
suites = ["club", "diamond", "heart", "spade"]
specials = [{"name":"black_joker","x":0, "y":4}, {"name":"red_joker","x":1, "y":4}, {"name":"back","x":2, "y":4}]
for suite_number, suite in enumerate(suites):
    for card_number, card in enumerate(card_names):
        print "processing", suite, card, '#'+card+'_'+suite
        pixbuf = svg.get_pixbuf(id='#'+card+'_'+suite)
        pixbuf.subpixbuf(int(w*card_number), int(h*suite_number), int(w), int(h)).save("./"+card+"_"+suite+".png","png", {})
for special in specials:
    print "processing", special["name"]
    pixbuf = svg.get_pixbuf(id='#'+special["name"])
    card_number = special["x"]
    suite_number = special["y"]
    pixbuf.subpixbuf(int(w*card_number), int(h*suite_number), int(w), int(h)).save("./"+special["name"]+".png","png", {})

Bugbear

Answer 3

Grave-digging a little bit here, but the answer by ptomato from 2010 also works now in 2019 for Gtk3 with some slight modifications. The below code will render only the 3 of diamonds svg id.

#!/usr/bin/env python

import gi
gi.require_version('Gtk', '3.0')
gi.require_version('Rsvg', '2.0')

from gi.repository import Gtk, Rsvg

svg = Rsvg.Handle.new_from_file('svg-cards.svg')

pixbuf = svg.get_pixbuf_sub('#3_diamond')

image = Gtk.Image()
image.set_from_pixbuf(pixbuf)
image.show()

window = Gtk.Window()
window.set_title("Foo")
window.connect("destroy", Gtk.main_quit)
window.show()
window.add(image)

Gtk.main()

Monaural

Answer 4

I believe that what he means by 'through a DOM interface' is that since SVG is XML, you could load the SVG file in minidom, or some other Python XML parser, and extract the XML node with the specific name that you are looking for. That XML node should represent an item that can be rendered.

Colucci

How do you render the XML node? – Gallic

Answer 5

You can do it by editing the tag. Edit width and height, set the viewBox attribute on the main svg element to the rectangle you want, render, repeat.

See How to show a subsection or "slice" of an SVG graphic? and http://dingoskidneys.com/~dholth/svg/

Andromache

This doesn't help me retrieve parts of the SVG file by name and then render them. – Gallic

You might be able to get the bounding box for named parts of the SVG file and set the viewBox accordingly. – Andromache