get-text-extent errors for a bitmap-dc% object without a bitmap installed

[rymaju]

Hi! 👋
Found an inconsistency with current behavior and the docs, thought it was worth making an issue.

Per the documentation at https://docs.racket-lang.org/draw/bitmap-dc_.html

A bitmap% object must be supplied at initialization or installed into a bitmap DC using set-bitmap before any other method of the DC is called, except get-text-extent, get-char-height, or get-char-width. If any other bitmap-dc% method is called before a bitmap is selected, the method call is ignored.

Also in the docs for get-text-extent

Unlike most methods, this method can be called for a bitmap-dc% object without a bitmap installed.

However, when I try:

(define text-size-dc-unset (new bitmap-dc%))
(send text-size-dc-unset get-text-extent "Pickles")

I get an error:

get-text-extent in dc<%>: drawing context is not ok: (wrapper-object:bitmap-dc% ...)

Which probably comes from here:

draw/draw-lib/racket/draw/private/dc.rkt

Line 1363 in 01e00ba

(check-ok 'get-text-extent)

The other two methods, get-char-width and get-char-height work fine, its just this one :/

I'm using Racket v8.4 on a MacBook Pro (2019).

[rymaju]

After trying to patch this locally I was able to narrow it down it a little further. I took out the check-ok, which of course got rid of the error but led to some unsatisfactory results.

It looks like what I'm running into is that the cr used here

draw/draw-lib/racket/draw/private/dc.rkt

Lines 1390 to 1395 in 01e00ba

	(if w
	(values w h d a)
	(with-unchanged-cr
	(values 1.0 1.0 0.0 0.0)
	cr
	(do-text cr #f s 0 0 use-font combine? offset 0.0))))))

is #f when the bitmap is uninstalled, which causes the method to return 1 1 0 0.

Not exactly sure where to go from here, so thats where my exploration ends 😅 Hope that helps!