[AD] RLE sprites and AllegroGL

[Bertrand Coconnier <bcoconni@xxxxxxxxxx>]

The Allegro driver in AllegroGL is currently under developement. As a 
reminder, the "Allegro driver" of AGL is intended to allow the user to 
use Allegro's gfx functions over an OpenGL background : AGL then 
translates each Allegro gfx requests into GL commands (and eventually 
does some magic ^_^ ) in order to obtain the desired result.

Most of the methods of the GFX_VTABLE have been implemented so far but 
some of them still need to be written. I am currently developing the 
method to draw a RLE sprite onto the screen and I think that the RLE 
struct lacks an "extra" pointer. The point is that whereas the BITMAP 
struct provides a so-called "extra" pointer to implement, well... , 
extra functionalities, the RLE struct lacks such an option. From an 
AllegroGL point of view,  since a RLE sprite can not be modified but can 
just (quoting the docs) be blasted onto a bitmap, it is a good candidate 
for being cached into texture memory. However, in order to do that, we 
need to keep track of some datas (including the texture ID that would 
contain the RLE sprite) and the best place to store such datas is the 
RLE struct itself. Hence the need for an "extra" pointer.

In order to mimic the BITMAP design, the patch also adds a method 
"destroy_rle_sprite" to the SYSTEM_DRIVER struct. The purpose is of 
course to allow extra datas to be correctly deleted by Allegro and 
(again from an AGL point of view) to provide a way to release its 
corresponding texture space when it is no longer needed.

I am aware that, since it breaks the ABI, the patch can not be added to 
the 4.0.x branch but I would appreciate that you consider its inclusion 
into the 4.1.x branch. Notice however that this patch is not that 
important for the AGL developement to continue but if you commit it, it 
will allow a major speed improvement for RLE sprites in AGL including 
for low-end graphics card (and is not speed improvement a major 
advantage of RLE sprites ? ^_^).

By the way, it has been a while since the last time I built a CVS 
version of Allegro and (shame on me) I could not remind how to build 
Allegro from CVS scratch. I have to admit moreover that it took me a 
while in order to discover that installation docs are now hidden in 
docs/build. May be I am dumb ^_^ but I guess I am not the only one (or 
am I ? ^_^) so may I suggest you to add the well-known "install" file at 
the Allegro root directory ? It could contain something like "Bad luck 
dude! Try docs/build instead", well... you get the point.

That's all ^_^.

   Bertrand.

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