Re: making an ipelet for changing a straight line

----------------------------------------------------------------------
-- compute lengths ipelet
----------------------------------------------------------------------
--[[

    This file is part of the extensible drawing editor Ipe.
    Copyright (C) 2010

    Ipe is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    Ipe is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
    License for more details.

    You should have received a copy of the GNU General Public License
    along with Ipe; if not, you can find it at
    "http://www.gnu.org/copyleft/gpl.html", or write to the Free
    Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

    written by Günter Rote, 2010.

--]]

label = "length of a geometric graph"

about = [[
length of a geometric graph

This ipelet is part of the Dagstuhl collection.
]]

----------------------------------------------------------
----------------------------------------------------------
-- This is the "length" function of a single edge.
-- Change it to your needs

local function norm(v) -- v is an ipe.Vector
  return v:len()
end

local objective_function_name = "Euclidean (L2)"

-- For the squared Euclidean length, uncomment the following 4 lines:

-- local function norm(v)
--   return v:sqLen()
-- end
-- local objective_function_name = "squared Euclidean"
----------------------------------------------------------
----------------------------------------------------------

local function c(p,q)
    local dif = p-q
    return norm(dif)
end

local function incorrect_input(model,s)
  model:warning("Cannot compute length", s)
end

function tlength(model)
  local p = model:page()
  local prim = p:primarySelection()
  local sec

  if not prim then model.ui:explain("no selection") return end

--  local seg = p[prim]
--  if seg:type() ~= "path" then
--     incorrect_input(model,"Primary selection is not a segment")
--     return
--  end
--  local shape = seg:shape()
--  if --shape ~= 1 or shape[1].type ~= "curve" or
--    --shape[1] ~= 1 or shape[1][1].type ~= "segment" then
--     incorrect_input(model,"Primary selection is not a segment")
 --    return
 -- end

--  local p0 = seg:matrix() * shape[1][1][1]
--  local p1 = seg:matrix() * shape[1][1][2]
--  local offset = p1-p0
--  local eps = offset:len()

  local w
  local warn = false
  local total = 0
  for i,obj,sel,layer in p:objects() do
   if sel then
     if (obj:type() ~= "path") then
      incorrect_input(model,"Some secondary selection is of type "..
          obj:type()..", not a path")
      return
     end
     shape = obj:shape()
     for ind,subpath in ipairs(shape) do
      if subpath.type ~= "curve" then
       incorrect_input(model,"Some secondary selection is not a polygonal path")
       return
      end
      for i,s in ipairs(subpath) do
       if s.type ~= "segment" then
        incorrect_input(model,"Some secondary selection is not a polygonal path")
        return
       end
       total = total + c(obj:matrix()*s[1],obj:matrix()*s[2])
      end
      if subpath.closed then
       total = total + c(obj:matrix()*subpath[#subpath][2], obj:matrix()*subpath[1][1])
      end
     end
    end
  end
-------- Now we have computed the length

  local outp = objective_function_name .." length="..total
  print (outp)
  model.ui:explain(outp)
end

run = tlength