[Ipe-discuss] Re: Get point coordinates in ipelets. (correction)

[Günter Rote]

Günter Rote wrote:
>> From: "Sebastien Loriot (GeometryFactory)" <sloriot.ml at gmail.com>
>> Subject: Re: [Ipe-discuss] CGAL points generator ipelets in Ipe 7
>>
>>> I'm writing an Ipelet in Lua that uses a set of points (markers) as 
>>> input. I sort the points using their x coordinate, which I obtain 
>>> using the getPosition() function of each marker object.
> 
> ...
> 
>>> ¿Does anybody have any idea of why this happens?, ¿Are not all the 
>>> objects on a page referenced to the same coordinate system?
>>>
>>
>> Just a hint: ... You probably should have a look at the matrix() 
>> function of ipe::Object.
>>
> 
> Here is an ipelet print.lua that dumps the coordinates of a group of points
> to the terminal (written for my own convenience), assuming
> that you start ipe from the command line.

This ipelet had a bug, because I forgot another matrix to multiply with,
see below.

> 
> 
> --[[
>     written by Günter Rote, 2010
> --]]
> 
> label = "print point coordinates"
> 
> about = [[
> Dump coordinates of a point set
> 
> This ipelet is part of Acrobat Reader.
> ]]
> 
> 
> local function incorrect_input(model,s)
>   model:warning("Cannot find coordinates", s)
> end
> 
> local function getpoints(model,obj,which)
>   if obj:type() ~= "group" then
>      incorrect_input(model, which .. " selection is not a group")
>      return
>   end
>   local marks={}
>   for i,point in ipairs(obj:elements()) do
>       if point:type() ~= "reference" or point:symbol():sub(1,5) ~= 
> "mark/" then
>         incorrect_input(model, which .. " selection is not a group of 
> points")
>         return
>       end

The following is wrong

>       marks[#marks + 1] = obj:matrix() * point:position()

here is the corrected statement

         marks[#marks + 1] = obj:matrix() * point:matrix() * point:position()

>   end
>   return marks
> end
> 
> function match(model)
>   local p = model:page()
>   local prim = p:primarySelection()
> 
> -- get the data
>   local p = getpoints(model,p[prim],"first")
>   if not p then
>    return
>   end
> 
> -- now print the data
> 
>   print ("[")
>   for i,ps in ipairs(p) do
>     print ("("..ps.x..","..ps.y .."),")
>   end
>   print ("]")
> 
> end
> 
> run = match
> 
> 
 >

[cristo] wrote:
 >> Thanks a lot for your answer, everything works perfect now. Just a question, why do 
you >make the test point:symbol():sub(1,5) ~= "mark/"?, are there reference objects that 
are >not a mark?

 >I don't know. I copied this from some other ipelet, namely:

function parabola(model) in goodies.lua


-- 
G"unter Rote               (Germany=49)30-838-75150 (office)
Freie Universit"at Berlin                    -75103 (secretary)
Institut f"ur Informatik       FAX (49)30-838-75192
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D-14195 Berlin, GERMANY  electronic mail: rote at inf.fu-berlin.de