Holy cow, I wrote a book!
Commenter kero wants to know
why the PrintWindow function hates
Because everybody hates
We saw earlier that these class styles
violate widely-held assumptions about how drawing works.
I mean, who would have thought that asking for two device
contexts would give you the same one back twice?
Or that changes to one device context would secretly modify another
(because they're really the same)?
Or that a window procedure assumes that it will see only
one device context ever?
The PrintWindow function is really in a pickle
when faced with a window with one of these class styles,
because the whole point of PrintWindow is
to render into some other device context.
The PrintWindow function says
"Render into this other device context, please,"
and the window acts like a bratty two-year-old who refuses
to eat food from anything other than his favorite
"This is not my monkey plate. I will now throw a tantrum."
The PrintWindow function
passes a custom device context as a parameter
to the WM_PRINT message,
and the window says,
"Hey, no fair!
My class styles say that you aren't allowed to pass any old
you have to pass mine.
I will now take my broccoli and mash it all over the table."
At least it tried.
Yet another reason to avoid these weird class styles.