mlib plugin question

[Peter Rolf <indiego@gmx.net>]

Hi,

I use a mlib plugin to manually start/stop transparency. All graphics
in between will be drawn with the defined state. Not very useful in
general, but I need it for some graphics in Aero.

This is the simple code..

MP side:

def btransp(expr a, t) =
    draw origin withprescript "mtr_transp=start"
        withprescript "mtr_alternative=" & decimal a
        withprescript "mtr_transparency=" & decimal t  ;
enddef ;

def etransp =
    draw origin withprescript "mtr_transp=stop" ;
enddef ;


TEX side:

local function mtr_process(object,prescript,before,after)
    local mtr_alternative = prescript.mtr_alternative
    if prescript.mtr_transp == "start" then
        if mtr_alternative then
            mtr_alternative = tonumber(mtr_alternative)
            local mtr_transparency = tonumber(prescript.mtr_transparency)
            before[#before+1] = format("q /Tr%s gs %%
mtr",registertransparency(nil,mtr_alternative,mtr_transparency,true))
        end
    elseif prescript.mtr_transp == "stop" then
        after[#after+1] = "Q % mtr"
    else
        -- fatal error
    end
--    object.path = true -- 'true' gives runtime error, 'false' distorts
content
    object.grouped = true
    object.type = false -- don't draw
    object.color = false
end

Usage:

btransp(normaltransparency,.5);
<whatever>
etransp;


This works so far (no visible artefacts), but part of the 'draw origin'
is (although not drawn) still existent in the code.

[..]
q /Tr1 gs % mtr
10.000000 M % unwanted setup for 'origin'
1 j
1 J
0.500000 w
0.000000 0.000000 m
0.000000 0.000000 l

<whatever>

10.000000 M % unwanted setup for 'origin'
1 j
1 J
0.500000 w
0.000000 0.000000 m
0.000000 0.000000 l
Q % mtr
[..]

I had a solution for the old 'specials', but I can't find one for the
plugin handler. How can I get rid of the 'trigger code'?


Peter
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