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On Mon, 2010-06-21 at 14:57 -0600, Thomas Fjellstrom wrote:
> Ok so today I had a little fun fighting with a bug in my code.
Turns out I
> was assuming al_transform_transform's first arg was the transform
to
> transform, and the second was the transform to transform by. Thats
> backwards.
>
> I was wondering if anyone else thinks that the current ordering is
> backwards? And if not, maybe the documentation could be clarified a
little,
> or at leas the names of the args could be a little less vague.
I would agree.
al_rotate_transform(Ta, b)
al_transform_transform(Rb, Ta)
al_transform_coordinates(Ta, x, y)
This has two problems. The first is probably what happened to you. If
Rb
is a transform which rotates around b, then it would make sense that
the
first and second line do exactly the same. Semantically, when
al_rotate_transform(Ta, b) says "rotate transform Ta by b" you'd
expect
that "al_transform_transform(Rb, Ta)" says "transform transform Rb
with
Ta" and *not* "transform transform Ta with Rb".
The second one is even more serious though. We agreed previously that
the transformation order is reversed compared to OpenGL, so whatever
appears earlier on in code is applied first. So in the above example
you
would assume:
First rotate by b.
Then apply Rb.
Then apply Ta.
However what really happens is this:
First rotate by b.
Then apply Ta.
Then apply Rb.
So two good reason to change it. The function
al_transform_coordinates(Ta, x, y) of course is inconsistent. Maybe we
can rename it to: al_apply_transform(Ta, x, y) so you would read it as
"Apply transformation Ta to the vector x, y."
Those seem like reasonable ideas, feel free to implement them (or wait
for me to do it eventually).
-SiegeLord