I'm creating an application that uses Cairo to display text over an image, among other things.

Is there a way I can change the text width without modifying the height? I can already scale the font size based on the width.

A way to manage tracking & kearning would be ideal. It doesn't look like that's built in, but I'd like to know what pieces I would use to build that functionality (or any functionality to modify only the width).

Pango / PangoCairo

Pango seems to offer a lot of customization.

Its Markup format allows you to specify letter_spacing.

I don't have an in-depth knowledge of the framework yet, but it's worth looking into.

Make your own function

You could also create a function to split a text into characters, display each one, move the context back a little after displaying each character. Something like the following:

# This is just an example. It could definitely use improvement.
def foo(cr, text, tracking): 
    # Normal tracking = 0. Negative spacing shrinks, positive expands.

    i = 0
    for c in text:
        x, y = cr.get_current_point()
        cr.show_text(c)
        counter += 1
        cr.move_to( x - i*tracking, y)

You could also define this method in your own subclass of Context:

class myContext(Context):
    def foo(self, text, spacing):
        # replace every cr above with self
        

Once you have a method set, you can just do foo(cr, "bob", -3) for a slimmer bob.

You can also use cr.text_extents(text) in your code to figure out text size & scale spacing. As far as I know, there's not an easy way to get the font size from a Context in Cairo.