Re: [pygame] BUG?: clip and Rect anomalies when width or height negative

["Paulo Silva" <nitrofurano@xxxxxxxxx>]

from the example i only can see 3 rectangles - green, blue and red.

But the negative situation you may say were those values being
negative, or smaller?

This may be some bug, which is expecting the late values should be
higher than the first ones (like x2,y2 about x1,y1) - and the bug may
be in the code not swapping these values when it happens

This situation also uses to happen in the sdlBasic interpreter as well

-----------------------------------------

On Sat, Oct 18, 2008 at 2:01 AM, claudio canepa <ccanepacc@xxxxxxxxx> wrote:
> 1. Clip Anomaly:
> when a surface .set_clip is called with a rect which have negative width or
> height,
>
> seems natural that following fills or blits don't touch at all the surface.
> But
> width<0 --> surface.get_clip().width == surface.get_width()
> height<0 --> surface.get_clip().height == surface.get_height()
> so if the left,top of the clip area is not too far you get the surface
> partially
>
> blited/filled.
>
> The attached clip_test.py demoes this.
>
> Use case:
> resizing the clip area in a loop can get the last loop iteration with a
>
> degenerated clip rect.
> The natural control variable for the loop is not the width.
> Expectation on set_clip behavior with negative width was that nothing would
> write
>
> to the surface, hence garbage in the screen. Because of unexpected, toke
> some time
>
> to find the problem.
>
> there is any rationale for the current behavior ?
> wouldn't be better my expected behavior ?
>
> If the current behavior will be kept, please mention it in the docs for
> set_clip
>
> and get_clip, and maybe blit / fill
>
>
> 2. Rect anomaly when width or height is negative:
>
> Look at this:
>
>>>> clip_rect = pygame.Rect(1,1,-100,-100)
>>>> clip_rect.width
> -100
>>>> clip_rect.left
> 1
>>>> clip_rect.right
> -99
>>>>
>
> Its reasonable that a Rect can serve a width<0 ?
> Its reasonable that rect.left>rect.right ?
>
> To me, this behavior broke the user expectations. Even if the 1.8.1 docs
> tells
>
> that "The size values can be programmed to have negative values, but these
> are
>
> considered illegal Rects for most operations. "
>
> Much better would be: Accept width or height negative, BUT convert to 0
> before
>
> store it internally.
> With that, the prev interpreter session would look:
>
>>>> clip_rect = pygame.Rect(1,1,-100,-100)
>>>> clip_rect.width
> 0
>>>> clip_rect.left
> 1
>>>> clip_rect.right
> 1
>>>>
>
> As a side effect, opers that uses rects like blit, fill, set_clip... don't
> need to
>
> be extended to the degenerate cases.
>
> comments ?
>
> --
> claxo
>
>