OpenEuphoria

Re: mathmatical question..

• Posted by David Alan Gay <moggie at INTERLOG.COM> May 29, 1997
• 1251 views

> Assumes the polygon with arbitrary numbers of points is drawn on the
> pixel-graphics screen, for example;
>
> polygon(RED,1,{{100,200},{200,200},......,}
>
> Problem is:
> How can I know whether the mouse pointer is INSIDE the polygon or not,
> at the time the mouse button is pressed?
>
> Bye!
> from Lee, WooSeob

It's not even a mathematical problem...it's more like a question of "Is the
mouse pointer over an image?"

There's two ways of attacking this. One way is to use get_pixel() using the
returned mouse x and y co-ordinates to obtain the pixel colour of where the
mouse pointer is at. In the case of your polygon above, you know you are
over the polygon if the colour RED is returned. Admittedly. it's not good
for a polygon with mulitple or shared colours, but it works if the polygon
is a complex shape.

Another way is to make a sequence representing a map of what space the
polygon occupies, and then search it using find() with the x and y mouse
pointer co-ordinates as the search argument. If you get a hit, you know you
are over the shape. This is much more preferable if the icon you are trying
to make clickable is multi-coloured.

Hope this helps

David Gay
http://www.digital-liquid.com/abgte
"A Beginner's Guide To Euphoria"