Re: [AD] clipping line algorithm

[Robert Jr Ohannessian <rohannessian@xxxxxxxxxx>]

Sven Sandberg wrote:
[snip]
> I think we should, for the following reasons:
>  - Backwards compatibility. bmp_read* and bmp_write* have been around 
> forever, and it would be a pity to break programs using them.

I agree.

>  - Speed. Since we don't implement all possible functionality in 
> Allegro, some of it has to be in add-ons, in user's programs, or in 
> generic modules somewhere inbetween the two. Those would benefit from 
> the additional speed of direct access rather than going through the vtable.

I disagree. bmp_* is fine to use on your normal Allegro bitmap. However, 
when it comes to odd bitmap types (modex, OpenGL, ...) bmp_* fails 
miserably in the speed department.


> > If not, then it doesn't matter, because all the Allegro API functions 
> > should route to some bitmap's vtable.
>
>
> This is not how it works at the moment: polygon(), 
> [scene_]polygon3d[_f](), draw_gouraud_sprite(), floodfill(), arc(), 
> spline(), rect() and others are all outside the vtable (see 
> include/allegro/gfx.h). Are you suggesting to move all such functions to 
> the vtable?


Yes, but that's a discussion for another thread.


> Good! So how should this be implemented? I gave two suggestions, both 
> based on flags in BITMAP->id, and you suggest a BITMAP->caps bitfield 
> with the same functionality. Pros and cons in my opinion:
>  - BITMAP->id seems like the easiest-to-implement solution. That's how 
> it is currently done.
>  - BITMAP->caps seems a bit more extendible in case we stumble on 
> anything else that a bitmap needs to be queried for. BITMAP->id also has 
> the drawback that the lowest bits (those not used by a flag) are used as 
> an integer, to identify sub-bitmaps.

We should move all the flags from BITMAP->id to BITMAP->flags 
(attributes of the bitmap) and BITMAP->caps (what can be done with it).

I don't think we'll be breaking source compatibility, appart perhaps for 
some add-ons.

We should get rid of the flags-in-id thing. It's bug-prone and very 
limiting. flags and caps could even be placed into the vtable, so we 
don't even need more memory for them.


--
- Robert Jr Ohannessian
http://bob.allegronetwork.com/