Disturbing bug in directional functions

[hertogjan]

It seems to me that quite a large bug has been introduced in the directional functions. This totally breaks the whole game, since road vehicles will all be stuck on corners. It seems that the following piece of code in direction.h is the cause of it.

Code: Select all

static inline DirDiff DirDifference(Direction d0, Direction d1)
{
	return (DirDiff)((d0 + 8 - d1) % 8);
}

I think this wouldn't work. The signed difference between a pair of numbers a, b is b-a, not a-b. This is to make sure that
a + difference(a, b) = b,
which should be what you expect. Defining it the other way around results in unnatural minus signs. This should be avoided since it causes bugs.

This should be fixed as soon as possible.
Moreover, I have a little message for the dev team: Please be a little more careful when adding or changing code!

[hertogjan]

It seems that it is fixed now. At least, the roadvehicles behave correctly now. However, the directional function is still in the wrong order. Or, at least, the parameter names (d0, d1) should be swapped, or be changed to something more instructive, like d_new and d_old for d0 and d1. At least it should be clear that the function does this

Code: Select all

static inline DirDiff DirDifference(Direction d_old, Direction d_new)
{
   return (DirDiff)((d_new + 8 - d_old) % 8);
}

Again, this is to prevent confusion and mistakes in the future.