Re: [AD] clipping line algorithm

[Sven Sandberg <svens@xxxxxxxxxx>]

Eric Botcazou wrote:
> > So it seems contradictory that users setting the linear flag both:
> > (1) must count with the possibility that _putpixel()/bmp_write() can be
> > used on it, and
> > (2) can be assured the bitmap is never accessed without going through
> > the vtable.
>
> On the one hand, I don't have any example and such an example would 
> admittedly be a little contrived.

Sorry, there must still be some misunderstanding. As I interpreted your 
previous message, you want the following to hold for bitmaps with the 
"linear" flag set:

(1) it is possible that someone uses bmp_read on the bitmap.
(2) it is impossible that someone accesses the bitmap without using the 
vtable.

However, the following is also true:

(3) bmp_read accesses the bitmap without using the vtable.

Combining (1) and (3), we derive:

(4) it is possible that someone accesses the bitmap without using the 
vtable.

But (4) contradicts (2).

So it is logically impossible that (1), (2) and (3) are true at the same 
time. Which of them do you not agree on?

/Sven