Re: [Boost-users] making a geometry half closed

Subject: Re: [Boost-users] making a geometry half closed
From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 2014-01-26 18:00:15

Hi,

Sean Farrow wrote:
>
> Hi,
>
> Ok, take a windows RECT structure:
>
> typedefstruct_RECT {
>
>   LONG left;
>
>   LONG top;
>
>   LONG right;
>
>   LONG bottom;
>
> } RECT, *PRECT;
>
> The remarks then state:
>
> By convention, the right and bottom edges of the rectangle are 
> normally considered exclusive. In other words, the pixel whose 
> coordinates are ( right, bottom ) lies immediately outside of the 
> rectangle. For example, when RECT is passed to the FillRect  function, 
> the rectangle is filled up to, but not including, the right column and 
> bottom row of pixels.
>
> How can I gain the same behaviour when doing equals, overlaps etc.?
>
> Any help appreciated.
>
> Cheers
>
> Sean.
>
> *From:*Boost-users [mailto:boost-users-bounces_at_[hidden]] *On 
> Behalf Of *Barend Gehrels
> *Sent:* 26 January 2014 21:49
> *To:* boost-users_at_[hidden]
> *Subject:* Re: [Boost-users] making a geometry half closed
>
> Hi Sean,
>
> Sean Farrow wrote On 26-1-2014 14:44:
>
>     Hi,
>
>     From what I understand any boost geometry is fully closed. Is
>     there a way of making a geometry half closed, such that the bottom
>     row is not included?
>
>     I'm needing to do this with a Box2D$Values.
>
>     Any help appreciated.
>
>
> No, this is not really implemented. Which problem do you have in mind? 
> For example a "touch" relationship where two geometries touch each 
> other, would this differ if they touch the upper row instead of the 
> lower row?
>
> The within-algorithm (for point-in-box) considers a point within if it 
> is completely inside. That can be finetuned by supplying a strategy 
> which considers bottom-row / right row.
>

The coordinates aren't floating points. Maybe using right-1 for 
<max_corner, 0> and bottom-1 for <max_corner, 1> could work? It probably 
depends on the use case.

Just a quick thought. Coordinates are increasing top-down right? E.g. 
polygons marked as CW in Boost.Geometry would appear as CCW on your screen.

Regards,
Adam