Re: [AD] 4.9.20

[Elias Pschernig <elias.pschernig@xxxxxxxxxx>]

On Mon, May 17, 2010 at 4:02 AM, Peter Wang <novalazy@xxxxxxxxxx> wrote:

Probably overdue for one, so I'll make it this weekend.

Are we ready to call it a beta?

Just remembered something we discussed in #allegro some time ago - there's a bit of an API ambiguity with transformation order:

al_identity_transform(t);

al_translate_transform(t, 100, 0);
al_rotate_transform(t, deg2rad(90));
al_use_transform(t);
al_draw_pixel(100, 0, red);

Someone who did not use any other libraries before Allegro might expect 
something like this:

The pixel is drawn at 100/0, but first gets translated to 200/0, then gets rotated 
to 0/200.

Everyone else probably will expect that the pixel first gets rotated to 0/100 and is then translated to 100/100. It's also what makes more sense usually. For example:

draw_ship() {
   *backup = *t;
   al_translate_transform(t, ship.x, ship.y);
   al_rotate_transform(t, ship.angle);
   al_use_transform(t);
   al_draw_triangle(...);
   *t = *backup;
}

draw_scene() {
   al_translate_transform(t, cam.x, cam.y);
   al_rotate_transform(t, cam.angle);
   draw_ship();
}

So I think best will be to rename the functions:

al_translate_transform -> al_pre_translate_transform
al_rotate_transform -> al_pre_rotate_transform
al_scale_transform -> al_pre_scale_transform
al_transform_transform -> al_pre_transform_transform

This makes clear that whatever transformation is applied to the passed transformation will be done *before* the existing transformation.

And maybe we can also have the _post_ versions.