Re: [Pysdl-devel] rect class, design help

[Jan E. <ch...@in...>]

On Sun, 17 Sep 2000, Pete Shinners wrote:

>--- should rects return nonzero if only one of width or
>height is 0? with a zero width or height, SDL isn't going
>to do anything during blits or fills. on the other hand,
>there is some size info still in there, this may be helpful
>in some cases.

><<rect will return nonzero only if both width and height
>are nonzero>>

IMO a rect with 0 height or width is valid. I could think of situations
where a rect needs to shrink for some reason until is is just a line with
no width/height. No blits would be done, of course.


>--- operator math? i've been trying to think of clean and
>useful cases to add operator math to the rectangle. (+-*%).
>it could be useful for "rect += (10, 40)" to move a
>rectangle. but there is effort needed to define all
>the cases with clean and consistent usage

><<not planning for this (at least in first release). if
>someone really wants this stuff, please compile a list
>of all the operators you'd like to use, as well as what
>types of arguments they can take and what the results
>should be>>

Personally I think I'd so far like plain methods for doing these kind of
things, such as resize(), move() etc. But I'm not too experieced with
Python yet, but in C++ I'd do it with methods.

>--- when changing rectangle attributes, should the rect
>automatically try to maintain non-negative values?

><<i'm currently planning to have the rect automatically fix
>negative sizes. yes, there's potential for confusion, but i
>can't think of a good case where one would actually want to
>keep the negative value. plus all of the rects method results
>become undefined when fed rects with negative sizes. so best
>to take the extra step to avoid them>>

Either automatically or then throw an exception. I'd maybe prefer to have
an exception, as "flipping" a rect indicates an error from the programmer.

>--- what should the return values/modification behavior be
>for all of the rectangle methods. in the standard python
>modules, the usual rule is, if a method changes the values
>of "self", then it returns none. otherwise the method returns
>a new object with the result of the changes, the original goes
>unchanged. (a potential third option is to change the original
>and return a reference to the original). ok, since this is
>the most important one i want to make sure everyone understands
>the full effects of this. for the method rect.clip, we have
>three main strategies.
>rect.clip can just change the rectangle it is working on ("self")
>    and return nothing.
>rect.clip can create a new rectangle with the results and return
>    that.
>rect.clip can modify "self" and return a reference to itself.
>ok, the three options may not sound to different, here are the
>CONS for each approach
>"Only Change Self": with this approach, everytime you want
>    to change something about a rect, it takes a separate
>    line. some things can require a couple steps, and it
>    makes it impossible to send values to functions with
>    'on the fly' changes'. think of the list methods, like
>    list.sort(), etc.

I'd like to use this way of doing things.

I look forward to be able to test your new class, as it can make
gui-making a lot easier. 

--------------------+--------------------------------------------------------
Jan 'Chakie' Ekholm |     Balrog New Media    http://www.balrog.fi/
   Linux Inside     | I'm the blue screen of death, nobody hears your screams