* Clipping a path to a boundary --- Being more specific
@ 2005-08-08 1:17 David Arnold
2005-08-08 13:20 ` Hans Hagen
0 siblings, 1 reply; 4+ messages in thread
From: David Arnold @ 2005-08-08 1:17 UTC (permalink / raw)
Hans et al,
Let me try to be more specific. Here is a file which is very typical of
the way I draw graphs for my mathematics classes. When you compile, you
will see the graph of the absolute value of x-1. That is, it draws the
graph of y=|x-1|, but only after clipping it to the cpath. What I
would like to do is draw the graph with the drawdblarrow command so
that the graph of the absolute value ends in arrowheads. So, I want to
clip the graph to the bounding box, save the picture, null the picture,
then somehow extract the path into the variable F in its clipped form
(not the original path F that extends outside the clip path) so that I
can replace the command draw pic with drawdblarrow F.
beginfig(0);
numeric a, c;
a=1;
% define function f(x)=|x-a|
vardef f(expr x)=
abs(x-a)
enddef;
% draw line with given point and slope
path F;
F:=(-5,f(-5));
for x=-5 step 1 until 5:
F:=F--(x,f(x));
endfor;
% initialize scale
numeric u; 10u=3in;
% the line
F:=F scaled 1u;
draw F withcolor blue;
% clipping path
path cpath;
cpath:=(-5,-5)--(5,-5)--(5,5)--(-5,5)--cycle;
cpath:=cpath scaled 1u;
% clip and save current picture
picture pic;
clip currentpicture to cpath;
pic:=currentpicture;
currentpicture:=nullpicture;
% erase currentpicture
currentpicture:=nullpicture;
% draw grid
for k=-5u step 1u until 5u:
draw (-5u,k)--(5u,k) withcolor 0.85white;
draw (k,-5u)--(k,5u) withcolor 0.85white;
endfor;
% draw axes
drawarrow (-5u,0)--(5u,0);
drawarrow (0,-5u)--(0,5u);
% label axes
label.rt(btex $x$ etex, (5.2u,0));
label.top(btex $y$ etex, (0,5.2.u));
label.bot(btex $5$ etex, (5u,0));
label.lft(btex $5$ etex, (0,5u));
% redraw line
draw pic;
endfig;
end.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Clipping a path to a boundary --- Being more specific
2005-08-08 1:17 Clipping a path to a boundary --- Being more specific David Arnold
@ 2005-08-08 13:20 ` Hans Hagen
2005-08-10 0:24 ` David Arnold
0 siblings, 1 reply; 4+ messages in thread
From: Hans Hagen @ 2005-08-08 13:20 UTC (permalink / raw)
David Arnold wrote:
> Hans et al,
>
> Let me try to be more specific. Here is a file which is very typical
> of the way I draw graphs for my mathematics classes. When you compile,
> you will see the graph of the absolute value of x-1. That is, it draws
> the graph of y=|x-1|, but only after clipping it to the cpath. What I
> would like to do is draw the graph with the drawdblarrow command so
> that the graph of the absolute value ends in arrowheads. So, I want to
> clip the graph to the bounding box, save the picture, null the
> picture, then somehow extract the path into the variable F in its
> clipped form (not the original path F that extends outside the clip
> path) so that I can replace the command draw pic with drawdblarrow F.
hm, this need some more brainpower than the previous solution,
in mp-tool there is a repathed macro that does most of the job so let's
extend that one a bit:
\starttext
\setupcolors[state=start]
\startMPpage
def restroke suffix p = p := repathed (21,p) enddef ; % keep attributes
def reprocess suffix p = p := repathed (22,p) enddef ; % no attributes
vardef repathed (expr mode, p) text t =
begingroup ;
if mode=0 : save withcolor ; remapcolors ; fi ;
save _p_, _pp_, _ppp_, _f_, _b_, _t_ ;
picture _p_, _pp_, _ppp_ ; color _f_ ; path _b_ ; transform _t_ ;
_b_ := boundingbox p ; _p_ := nullpicture ;
for i within p :
_f_ := (redpart i, greenpart i, bluepart i) ;
if bounded i :
_pp_ := repathed(mode,i) t ;
setbounds _pp_ to pathpart i ;
addto _p_ also _pp_ ;
elseif clipped i :
_pp_ := repathed(mode,i) t ;
clip _pp_ to pathpart i ;
addto _p_ also _pp_ ;
elseif stroked i :
if mode=21 :
_ppp_ := i ; % indirectness is needed
addto _p_ also image(scantokens(t & " pathpart _ppp_")
dashed dashpart i withpen penpart i
withcolor _f_ ; ) ;
elseif mode=22 :
_ppp_ := i ; % indirectness is needed
addto _p_ also image(scantokens(t & " pathpart _ppp_")) ;
else :
addto _p_ doublepath pathpart i
dashed dashpart i withpen penpart i
withcolor _f_ % (redpart i, greenpart i, bluepart i)
if mode=2 : t fi ;
fi ;
elseif filled i :
if mode=11 :
_ppp_ := i ; % indirectness is needed
addto _p_ also image(scantokens(t & " pathpart _ppp_")
withcolor _f_ ; ) ;
elseif mode=12 :
_ppp_ := i ; % indirectness is needed
addto _p_ also image(scantokens(t & " pathpart _ppp_")) ;
else :
addto _p_ contour pathpart i
withcolor _f_
if (mode=1) and (_f_<>refillbackground) : t fi ;
fi ;
elseif textual i : % textpart i <> "" :
if mode <> 4 :
addto _p_ also i if mode=3 : t fi ;
fi ;
else :
addto _p_ also i ;
fi ;
endfor ;
setbounds _p_ to _b_ ;
_p_
endgroup
enddef ;
picture pic; pic := image(
draw fullcircle scaled 5cm withpen pencircle scaled 5mm ;
draw fullsquare scaled 2cm withpen pencircle scaled 5mm ;
fill fullcircle scaled 1cm withpen pencircle scaled 5mm ;
) ;
redraw pic withpen pencircle scaled 1mm withcolor red ;
% restroke pic "drawdblarrow" ;
pic := repathed(21,pic) "drawdblarrow" ;
pic := repathed(11,pic) "drawdblarrow" ;
draw pic ;
\stopMPpage
\stoptext
the new restroke variant takes a macro name that itself takes one argument, i.e. a path, so in order to do more complex things, you need to define those
Hans
-----------------------------------------------------------------
Hans Hagen | PRAGMA ADE
Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
| www.pragma-pod.nl
-----------------------------------------------------------------
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Clipping a path to a boundary --- Being more specific
2005-08-08 13:20 ` Hans Hagen
@ 2005-08-10 0:24 ` David Arnold
2005-08-10 16:15 ` David Arnold
0 siblings, 1 reply; 4+ messages in thread
From: David Arnold @ 2005-08-10 0:24 UTC (permalink / raw)
Hans et al,
I tried what follows. But as far as I can see, I am not getting back a
path q that is clipped to the cpath.
vardef lastpath (expr p) =
save _p_ ; path _p_ ; _p_ := origin ;
for i within p :
if stroked i : _p_ := pathpart i ; fi ;
endfor ;
_p_
enddef ;
vardef firstpath (expr p) =
save _p_, _b_ ; path _p_ ; _p_ := origin ; boolean _b_ ; _b_ :=
false ;
for i within p :
if not _b_ : if stroked i : _b_ := true ; _p_ := pathpart i
; fi ; fi ;
endfor ;
_p_
enddef ;
beginfig(0);
%initialize a of f(x)=|x-a|
numeric a;
a=-2;
% initialize scale
numeric u; 10u=3in;
%function definition
vardef f(expr x)=
abs(x-a)
enddef;
%path
path F;
F:=(-5,f(-5));
for x=-5 step 1 until 5:
F:=F--(x,f(x));
endfor;
%scale and draw F
F:=F scaled u;
draw F withcolor blue;
%clip path
path cpath;
cpath:=(5,-5)--(5,5)--(-5,5)--(-5,-5)--cycle;
cpath:=cpath scaled u;
clip currentpicture to cpath;
%save and null currentpicture
picture pic;
pic:=currentpicture;
currentpicture:=nullpicture;
%retrieve first path
path q; q:=firstpath(pic);
%draw grid
for k=-5u step 1u until 5u:
draw (-5u,k)--(5u,k) withcolor 0.85white;
draw (k,-5u)--(k,5u) withcolor 0.85white;
endfor;
% draw axes
drawarrow (-5u,0)--(5u,0);
drawarrow (0,-5u)--(0,5u);
% label axes
label.rt(btex $x$ etex, (5.2u,0));
label.top(btex $y$ etex, (0,5.2.u));
label.bot(btex $5$ etex, (5u,0));
label.lft(btex $5$ etex, (0,5u));
drawdblarrow q withcolor blue;
endfig;
end.
On Aug 8, 2005, at 6:20 AM, Hans Hagen wrote:
> David Arnold wrote:
>
>> Hans et al,
>>
>> Let me try to be more specific. Here is a file which is very typical
>> of the way I draw graphs for my mathematics classes. When you
>> compile, you will see the graph of the absolute value of x-1. That
>> is, it draws the graph of y=|x-1|, but only after clipping it to the
>> cpath. What I would like to do is draw the graph with the
>> drawdblarrow command so that the graph of the absolute value ends in
>> arrowheads. So, I want to clip the graph to the bounding box, save
>> the picture, null the picture, then somehow extract the path into the
>> variable F in its clipped form (not the original path F that extends
>> outside the clip path) so that I can replace the command draw pic
>> with drawdblarrow F.
>
>
> hm, this need some more brainpower than the previous solution,
>
> in mp-tool there is a repathed macro that does most of the job so
> let's extend that one a bit:
>
> \starttext
>
> \setupcolors[state=start]
>
> \startMPpage
>
> def restroke suffix p = p := repathed (21,p) enddef ; % keep
> attributes
> def reprocess suffix p = p := repathed (22,p) enddef ; % no attributes
>
> vardef repathed (expr mode, p) text t =
> begingroup ;
> if mode=0 : save withcolor ; remapcolors ; fi ;
> save _p_, _pp_, _ppp_, _f_, _b_, _t_ ;
> picture _p_, _pp_, _ppp_ ; color _f_ ; path _b_ ; transform _t_ ;
> _b_ := boundingbox p ; _p_ := nullpicture ;
> for i within p :
> _f_ := (redpart i, greenpart i, bluepart i) ;
> if bounded i :
> _pp_ := repathed(mode,i) t ;
> setbounds _pp_ to pathpart i ;
> addto _p_ also _pp_ ;
> elseif clipped i :
> _pp_ := repathed(mode,i) t ;
> clip _pp_ to pathpart i ;
> addto _p_ also _pp_ ;
> elseif stroked i :
> if mode=21 :
> _ppp_ := i ; % indirectness is needed
> addto _p_ also image(scantokens(t & " pathpart _ppp_")
> dashed dashpart i withpen penpart i
> withcolor _f_ ; ) ;
> elseif mode=22 :
> _ppp_ := i ; % indirectness is needed
> addto _p_ also image(scantokens(t & " pathpart _ppp_")) ;
> else :
> addto _p_ doublepath pathpart i
> dashed dashpart i withpen penpart i
> withcolor _f_ % (redpart i, greenpart i, bluepart i)
> if mode=2 : t fi ;
> fi ;
> elseif filled i :
> if mode=11 :
> _ppp_ := i ; % indirectness is needed
> addto _p_ also image(scantokens(t & " pathpart _ppp_")
> withcolor _f_ ; ) ;
> elseif mode=12 :
> _ppp_ := i ; % indirectness is needed
> addto _p_ also image(scantokens(t & " pathpart _ppp_")) ;
> else :
> addto _p_ contour pathpart i
> withcolor _f_
> if (mode=1) and (_f_<>refillbackground) : t fi ;
> fi ;
> elseif textual i : % textpart i <> "" :
> if mode <> 4 :
> addto _p_ also i if mode=3 : t fi ;
> fi ;
> else :
> addto _p_ also i ;
> fi ;
> endfor ;
> setbounds _p_ to _b_ ;
> _p_
> endgroup
> enddef ;
>
>
> picture pic; pic := image(
> draw fullcircle scaled 5cm withpen pencircle scaled 5mm ;
> draw fullsquare scaled 2cm withpen pencircle scaled 5mm ;
> fill fullcircle scaled 1cm withpen pencircle scaled 5mm ;
> ) ;
>
> redraw pic withpen pencircle scaled 1mm withcolor red ;
> % restroke pic "drawdblarrow" ;
> pic := repathed(21,pic) "drawdblarrow" ;
> pic := repathed(11,pic) "drawdblarrow" ;
> draw pic ;
>
> \stopMPpage
>
> \stoptext
>
> the new restroke variant takes a macro name that itself takes one
> argument, i.e. a path, so in order to do more complex things, you need
> to define those
> Hans
> -----------------------------------------------------------------
> Hans Hagen | PRAGMA ADE
> Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
> tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
> | www.pragma-pod.nl
> -----------------------------------------------------------------
>
> _______________________________________________
> ntg-context mailing list
> ntg-context@ntg.nl
> http://www.ntg.nl/mailman/listinfo/ntg-context
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Clipping a path to a boundary --- Being more specific
2005-08-10 0:24 ` David Arnold
@ 2005-08-10 16:15 ` David Arnold
0 siblings, 0 replies; 4+ messages in thread
From: David Arnold @ 2005-08-10 16:15 UTC (permalink / raw)
Hans et al,
I think I've found something that works. I know ahead of time that
there will only be two crossings of the clipping path boundary (I make
sure of the by the parameters I choose):
beginfig(0);
% initialize a, h, and h for f(x)=ax^2+bx+c=a(x-h)^2+k
numeric a, h, k;
a=-1;
h=-3;
k=2;
% initialize scale
numeric u; 10u=3in;
% draw grid
for k=-5u step 1u until 5u:
draw (-5u,k)--(5u,k) withcolor 0.85white;
draw (k,-5u)--(k,5u) withcolor 0.85white;
endfor;
% draw axes
drawarrow (-5u,0)--(5u,0);
drawarrow (0,-5u)--(0,5u);
% label axes
label.rt(btex $x$ etex, (5.2u,0));
label.top(btex $y$ etex, (0,5.2.u));
label.bot(btex $5$ etex, (5u,0));
label.lft(btex $5$ etex, (0,5u));
% define function f(x)=a|x-b|+c
vardef f(expr x)=
a*(x-h)*(x-h)+k
enddef;
% draw line with given point and slope
path F;
F:=(-6,f(-6));
for x=-6 step .1 until 6:
F:=F--(x,f(x));
endfor;
% the line
F:=F scaled 1u;
% clipping path
path cpath;
cpath:=(-5,-5)--(5,-5)--(5,5)--(-5,5)--cycle;
cpath:=cpath scaled 1u;
% clip the path F
pair A, B;
F:=F cutbefore cpath;
F:=reverse F;
F:=F cutbefore cpath;
drawdblarrow F;
endfig;
end.
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2005-08-08 1:17 Clipping a path to a boundary --- Being more specific David Arnold
2005-08-08 13:20 ` Hans Hagen
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2005-08-10 16:15 ` David Arnold
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