[Newbies] Rectangles

Bert Freudenberg bert at freudenbergs.de
Fri May 26 16:31:38 UTC 2017

On Thu, May 25, 2017 at 5:19 AM, Ralph Boland <rpboland at gmail.com> wrote:

> I just attempted to draw a rectangle with dimensions  3 at 3 corner: 9 at 3.
> Nothing gets drawn.  The reason that nothing is drawn is that the width of
> the rectangle is 0.  This makes sense for real numbers but for a pixelated
> screen or other display medium the dimensions of the rectangle
> should be 1 x 7  not  0 x 6!?.  This is 7 pixels needed to draw, not 0.
> The same issues occur for the height of the rectangles.
> I would think that the way things work would cause all kinds of problems
> but since Rectangles are pretty basic, either I am wrong,
> or every bit of Squeak code using rectangles has adjusted accordingly.
> Please clarify.

​The coordinates refer to the imaginary lines between pixels. Thus, if you
draw a rectangle from x=4 to x=5 its width is 1.​ This is so that if you
draw multiple rectangles, they do not overlap (imagine drawing from 5 to 12
and from 12 to 19).

> How do Java and other languages handle this?

​Same. There's a nice illustration on this page:

​- Bert -​
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