Re: [AD] clipping line algorithm

[Eric Botcazou <ebotcazou@xxxxxxxxxx>]

> 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.

Damn! A mathematician :-)

> Which of them do you not agree on?

(2) is obviously false. I'd rewrite it as:

(2') Every drawing function should use (or optimize based on) the vtable, 
except if it is specifically intended to bypass it (e.g. _putpixel).

-- 
Eric Botcazou