OpenEuphoria

Re: The Euphoria Sub Commander project

• Posted by CChris <christian.cuvier at agr?culture.gouv.fr> Nov 18, 2007
• 585 views

don cole wrote:
> 
> Pete Lomax wrote:
> > 
> > don cole wrote:
> > > 
> > > 
> > > Could someone please explain the following code to me in detail? I'm
> > > especially
> > > confused by the
> > > {} brackets.
> > > 
> > > }}}
<eucode>
> > > 
> > > k=player --1 or 2
> > > cen={{120,360},{520,360}},     -- centers of clock
> > Two clocks, center of 1 is {120,360} and the centre of 2 is {520,360}
> > 
> > > r=100,     -- radius of clock
> > > rt=remaining time in secs
> > > 
> > > 
> > > Don Cole
> > >  
> > > function p2xy(atom r, atom a)   -- polar to xy
> > >    return {-r*sin(a),-r*cos(a)}
> > > end function
> > > 
> > > draw_line(colors[k],{cen[k],cen[k]+p2xy(r,rt/1800*PI)})
> > 
> > Draws a line from the centre of the clock to somewhere on the edge.
> > 
> > As sin/cos expect arguments in radians, 0..2*PI, and rt is 0..3600, the
> > number
> > of seconds in an hour, it is coded as /1800*PI rather than /3600*2*PI.
> > 
> > Now imagine a clock with the second hand pointing at 10 seconds past the
> > hour, drop
> a line to
> > the horizontal through the centre to make a right angled triange whose
> > longest
> side is the second</i>
> > hand. For a picture, see eg <a
> > href="http://www.mathsrevision.net/gcse/pages.php?page=39">http://www.mathsrevision.net/gcse/pages.php?page=39</a>
> > 
> >  From basic trig, the height of this triangle is r*sin(a) and the width is
> >  r*cos(a).
> > (I almost always get such the wrong way round on first attempt.) 
> > 
> > Lastly, rt is the remaining time, a hand pointing at 2 o'clock would be
> > (10/12)*3600
> > or 3000 seconds which should explain why the offsets from the clock centre
> > to
> > the tip of the arm are both returned as -ve.
> > 
> > Hope that is enough detail for you there,
> > Pete
> 
>   I want to thank everyone who responded.
> 
> I kind of figured it out after I went to bed last night. It was the adding to
> cen[k] that confused me. cen[k] is a two element sequence the starting point
> of the line. The return of p2xy() is also a two element sequence. I guess you
> can add sequences together if they are the same length. This gives a third
> sequence
> which is where to put the end of the line.
> 
> 
> Don Cole

Well yes, it is actually one of the strengths of Euphoria that you can do s = s1
+ s2 and that this adds the two vectors together, provided their structures
match. This works with and, or, xor,-,* and /, but not & unfortunately. All math
operations (tan(), sqrt() and friends) also work like this. You'll get a complete
picture in the docs, section 2.2.4 (Operations on sequences).

For some background on sequence operations in Eu, see
 
http://www.openeuphoria.org/cgi-bin/esearch.exu?fromMonth=6&fromYear=1&toMonth=B&toYear=C&postedBy=robert+craig&keywords=background+on+sequence+operations

(URL wraps, see post #1 there). Strangely, I cannot find this post on Topica,
even though the replies do appear. The post is too old to be viewed here, even
with the several pages recent enhancement.

CChris