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* drawarrow and transparency
@ 2012-05-02 15:35 Alan BRASLAU
  2012-05-02 19:42 ` Marco
  2012-05-05  9:19 ` Hans Hagen
  0 siblings, 2 replies; 6+ messages in thread
From: Alan BRASLAU @ 2012-05-02 15:35 UTC (permalink / raw)
  To: mailing list for ConTeXt users

I have a MetaPost question concerning drawarrow withtransparency
(or any other compound object).

Is there some clever way to achieve uniform transparency
for a compound object? For example, in the minimal example
below, how can one obtain a transparent arrow without getting
an X-ray vision of the arrowhead?

\starttext
\startMPpage
	drawarrow origin--(1cm,0) withtransparency(1,.5) ;
	drawarrow origin--(0,1cm) withtransparency(1,.5) ;
\stopMPpage
\stoptext

Alan
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^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: drawarrow and transparency
  2012-05-02 15:35 drawarrow and transparency Alan BRASLAU
@ 2012-05-02 19:42 ` Marco
  2012-05-03 10:32   ` Alan BRASLAU
  2012-05-05  9:19 ` Hans Hagen
  1 sibling, 1 reply; 6+ messages in thread
From: Marco @ 2012-05-02 19:42 UTC (permalink / raw)
  To: ntg-context

On 2012-05-02 Alan BRASLAU <alan.braslau@cea.fr> wrote:

> For  example, in  the minimal  example below,  how can  one obtain
> a  transparent  arrow  without  getting an  X-ray  vision  of  the
> arrowhead?

Maybe I'm  reinventing the  wheel here,  but you  can write  a small
macro that only draws the lines you want. Here is an idea:

\starttext
\startMPpage

	linecap  := squared;
	penscale := .5bp;
	pickup pencircle scaled penscale;

	def drawmyarrow expr p = _apth:=p; _myfinarr enddef;
	def _myfinarr text t =
		draw _apth cutafter point (-ahlength+.1penscale) on _apth t;
		fill arrowhead _apth  t
	enddef;

	drawarrow   origin    -- (1cm,0)     withtransparency(1,.5) ;
	drawarrow   origin    -- (0,1cm)     withtransparency(1,.5) ;
	drawmyarrow (1.5cm,0) -- (2.5cm,0)   withtransparency(1,.5) ;
	drawmyarrow (1.5cm,0) -- (1.5cm,1cm) withtransparency(1,.5) ;

\stopMPpage
\stoptext

The (-ahlength+.1penscale)  are of  course empiric. You  should find
the correct  formula to always have  a nice match of  line and arrow
whatever ahlength and ahangle values are in use.

Marco


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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: drawarrow and transparency
  2012-05-02 19:42 ` Marco
@ 2012-05-03 10:32   ` Alan BRASLAU
  2012-05-03 12:47     ` Rogers, Michael K
  2012-05-03 14:09     ` Peter Rolf
  0 siblings, 2 replies; 6+ messages in thread
From: Alan BRASLAU @ 2012-05-03 10:32 UTC (permalink / raw)
  To: mailing list for ConTeXt users

On Wed, 2 May 2012 21:42:24 +0200
Marco <netuse@lavabit.com> wrote:

> On 2012-05-02 Alan BRASLAU <alan.braslau@cea.fr> wrote:
> 
> > For  example, in  the minimal  example below,  how can  one obtain
> > a  transparent  arrow  without  getting an  X-ray  vision  of  the
> > arrowhead?
> 
> Maybe I'm  reinventing the  wheel here,  but you  can write  a small
> macro that only draws the lines you want. Here is an idea:
> 
> \starttext
> \startMPpage
> 
> 	linecap  := squared;
> 	penscale := .5bp;
> 	pickup pencircle scaled penscale;
> 
> 	def drawmyarrow expr p = _apth:=p; _myfinarr enddef;
> 	def _myfinarr text t =
> 		draw _apth cutafter point (-ahlength+.1penscale) on
> _apth t; fill arrowhead _apth  t
> 	enddef;
> 
> 	drawarrow   origin    -- (1cm,0)     withtransparency(1,.5) ;
> 	drawarrow   origin    -- (0,1cm)     withtransparency(1,.5) ;
> 	drawmyarrow (1.5cm,0) -- (2.5cm,0)   withtransparency(1,.5) ;
> 	drawmyarrow (1.5cm,0) -- (1.5cm,1cm) withtransparency(1,.5) ;
> 
> \stopMPpage
> \stoptext
> 
> The (-ahlength+.1penscale)  are of  course empiric. You  should find
> the correct  formula to always have  a nice match of  line and arrow
> whatever ahlength and ahangle values are in use.
> 
> Marco

Yes, this is somewhat reinventing the wheel.

I believe that this is somewhat a bug with transparency under MetaFun.
For I tried the following:

\startMPcode
	picture pic ; pic := image(drawarrow origin--(1cm,0)) ;

	draw pic withtransparency(1,.5) ;
	draw pic rotated 90 withtransparency(1,.5) ;
\stopMPcode

Here, the arrowhead is totally opaque and only the "stem"
has transparency. Something is fishy.

Alan
___________________________________________________________________________________
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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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archive  : http://foundry.supelec.fr/projects/contextrev/
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___________________________________________________________________________________


^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: drawarrow and transparency
  2012-05-03 10:32   ` Alan BRASLAU
@ 2012-05-03 12:47     ` Rogers, Michael K
  2012-05-03 14:09     ` Peter Rolf
  1 sibling, 0 replies; 6+ messages in thread
From: Rogers, Michael K @ 2012-05-03 12:47 UTC (permalink / raw)
  To: mailing list for ConTeXt users


[-- Attachment #1.1: Type: text/plain, Size: 1714 bytes --]

On May 3, 2012, at 6:32 AM, Alan BRASLAU wrote:

I believe that this is somewhat a bug with transparency under MetaFun.
For I tried the following:

\startMPcode
picture pic ; pic := image(drawarrow origin--(1cm,0)) ;

draw pic withtransparency(1,.5) ;
draw pic rotated 90 withtransparency(1,.5) ;
\stopMPcode

Here, the arrowhead is totally opaque and only the "stem"
has transparency. Something is fishy.

Alan

I noticed the same thing.  I think original problem is with how an arrow is converted to PDF/Postscript drawing commands and how the color is computed when commands are combined.  The only solution I can imagine is to define a new arrow macro that constructs the boundary path of the arrow and fills it (i.e., up one side of the stem, around the arrowhead, and down the other side of the stem).  As far as I can tell, MetaPost/Postscript does not have commands that compute the boundary path of the region painted by a sequence of commands.  (I think that computing the boundary might be a much harder problem in general than computing which points to paint.  A straight arrow would be fairly simple.)

Michael

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___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
archive  : http://foundry.supelec.fr/projects/contextrev/
wiki     : http://contextgarden.net
___________________________________________________________________________________

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: drawarrow and transparency
  2012-05-03 10:32   ` Alan BRASLAU
  2012-05-03 12:47     ` Rogers, Michael K
@ 2012-05-03 14:09     ` Peter Rolf
  1 sibling, 0 replies; 6+ messages in thread
From: Peter Rolf @ 2012-05-03 14:09 UTC (permalink / raw)
  To: ntg-context

Hi Alan,

Am 03.05.2012 12:32, schrieb Alan BRASLAU:
> On Wed, 2 May 2012 21:42:24 +0200
> Marco <netuse@lavabit.com> wrote:
> 
>> On 2012-05-02 Alan BRASLAU <alan.braslau@cea.fr> wrote:
>>
>>> For  example, in  the minimal  example below,  how can  one obtain
>>> a  transparent  arrow  without  getting an  X-ray  vision  of  the
>>> arrowhead?
>>
>> Maybe I'm  reinventing the  wheel here,  but you  can write  a small
>> macro that only draws the lines you want. Here is an idea:
>>
>> \starttext
>> \startMPpage
>>
>> 	linecap  := squared;
>> 	penscale := .5bp;
>> 	pickup pencircle scaled penscale;
>>
>> 	def drawmyarrow expr p = _apth:=p; _myfinarr enddef;
>> 	def _myfinarr text t =
>> 		draw _apth cutafter point (-ahlength+.1penscale) on
>> _apth t; fill arrowhead _apth  t
>> 	enddef;
>>
>> 	drawarrow   origin    -- (1cm,0)     withtransparency(1,.5) ;
>> 	drawarrow   origin    -- (0,1cm)     withtransparency(1,.5) ;
>> 	drawmyarrow (1.5cm,0) -- (2.5cm,0)   withtransparency(1,.5) ;
>> 	drawmyarrow (1.5cm,0) -- (1.5cm,1cm) withtransparency(1,.5) ;
>>
>> \stopMPpage
>> \stoptext
>>
>> The (-ahlength+.1penscale)  are of  course empiric. You  should find
>> the correct  formula to always have  a nice match of  line and arrow
>> whatever ahlength and ahangle values are in use.
>>
>> Marco
> 
> Yes, this is somewhat reinventing the wheel.
> 
> I believe that this is somewhat a bug with transparency under MetaFun.
> For I tried the following:
> 
> \startMPcode
> 	picture pic ; pic := image(drawarrow origin--(1cm,0)) ;
>

isn't 'image()' a fixed graphic? the only difference from normal drawing
is, that the stuff is not added to 'currentpicture'. think of it more
like a stamp, that is used to create identical copies.

anyhow, it's probably better and cleaner to use a macro here...

> 	draw pic withtransparency(1,.5) ;
> 	draw pic rotated 90 withtransparency(1,.5) ;
> \stopMPcode
> 
> Here, the arrowhead is totally opaque and only the "stem"
> has transparency. Something is fishy.
> 
> Alan

what you want (if i understand you right) is a non-isolated 'knockout
group'. see 'PLATE 17'**, page 1147, in the pdf reference 1.7 for an
example.

currently no grouping (objects are in the same transparency group) is
supported in metafun.
the only possible way to create such a graphic is to use the tikz module
(search for 'transparency group' in the tikz manual).


hope that helps,

Peter


** the complete graphic is a fake, because all of its parts are opaque,
pixel based graphics; not a single vector graphic, no transparency at
all! what a joke :-D
maybe adobe doesn't trust other (or their own) pdf viewers to show the
right result!?
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
archive  : http://foundry.supelec.fr/projects/contextrev/
wiki     : http://contextgarden.net
___________________________________________________________________________________


^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: drawarrow and transparency
  2012-05-02 15:35 drawarrow and transparency Alan BRASLAU
  2012-05-02 19:42 ` Marco
@ 2012-05-05  9:19 ` Hans Hagen
  1 sibling, 0 replies; 6+ messages in thread
From: Hans Hagen @ 2012-05-05  9:19 UTC (permalink / raw)
  To: mailing list for ConTeXt users

On 2-5-2012 17:35, Alan BRASLAU wrote:
> I have a MetaPost question concerning drawarrow withtransparency
> (or any other compound object).
>
> Is there some clever way to achieve uniform transparency
> for a compound object? For example, in the minimal example
> below, how can one obtain a transparent arrow without getting
> an X-ray vision of the arrowhead?
>
> \starttext
> \startMPpage
> 	drawarrow origin--(1cm,0) withtransparency(1,.5) ;
> 	drawarrow origin--(0,1cm) withtransparency(1,.5) ;
> \stopMPpage
> \stoptext

This is a side effect of an arrow being a composed graphic. I 
experimented a bit with transparency grouping and after several variants 
I settled to the following approach:

\starttext

\startMPpage[offset=1mm]

     drawarrow (1cm,0cm) -- (0cm,0cm) withcolor red 
withtransparency(1,.5)  ;

     draw image (
         drawarrow (1cm,0cm) -- (0cm,0cm) withcolor red 
withtransparency(1,.5)  ;
     ) shifted (0,2mm) asgroup "" ;

     draw image (
         drawarrow (1cm,0cm) -- (0cm,0cm) withcolor red 
withtransparency(1,.5)  ;
     ) shifted (0,4mm) asgroup "isolated" ;

     draw image (
         drawarrow (1cm,0cm) -- (0cm,0cm) withcolor red 
withtransparency(1,.5)  ;
     ) shifted (0,6mm) asgroup "knockout" ;

     draw image (
         drawarrow (1cm,0cm) -- (0cm,0cm) withcolor red 
withtransparency(1,.5)  ;
     ) shifted (0,8mm) asgroup "isolated,knockout" ;

     addbackground withcolor green ;

\stopMPpage

\stoptext

As we have to use xforms (a pitty that this is needed) there is the 
usual interference and something fishy with clipping is going on.

Hans

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If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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___________________________________________________________________________________


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-05-05  9:19 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-05-02 15:35 drawarrow and transparency Alan BRASLAU
2012-05-02 19:42 ` Marco
2012-05-03 10:32   ` Alan BRASLAU
2012-05-03 12:47     ` Rogers, Michael K
2012-05-03 14:09     ` Peter Rolf
2012-05-05  9:19 ` Hans Hagen

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