MetaFun path joiners && and &&&& do not like single point paths
Hi MetaFun fans, Following a suggestion of Hans, I experimented with && and &&& and &&&& for joining paths in MetaFun. The joiner &&& produces one long path, but && and &&&& seem to produce a disconnected path which includes all the original paths. However, if one of the paths is a single point, then it connects it. MWE below. I spotted this on my globes module, where we saw an extra line appear for a very specific orientation of the globe. I guessed that this orientation had an island right on the horizon, so that only one boundary point was visible, creating a singe point path for that island. I should probably fix my module so it doesn’t do that. However, it might be nice to have && and &&&& deal with this situation gracefully. Gavin \startMPpage path p[], q ; p1 = fullcircle scaled 3cm ; p2 = fullcircle scaled 2cm shifted (3cm,0) ; p3 = (3cm,2cm) ; q = for i = 1 upto 3 : p[i] && endfor cycle ; draw p1 withpen pencircle scaled 2pt withcolor .7 ; draw p2 withpen pencircle scaled 2pt withcolor .7 ; draw p3 withpen pencircle scaled 2pt withcolor .7 ; draw q withcolor red ; eofill q withcolor 0.9 ; draw fullcircle scaled 6cm shifted (1.25cm,0) ; \stopMPpage
Hi
On Sun, Dec 31, 2023 at 3:33 AM Gavin via ntgcontext
Hi MetaFun fans,
Following a suggestion of Hans, I experimented with && and &&& and &&&& for joining paths in MetaFun. The joiner &&& produces one long path, but && and &&&& seem to produce a disconnected path which includes all the original paths. However, if one of the paths is a single point, then it connects it. MWE below.
I spotted this on my globes module, where we saw an extra line appear for a very specific orientation of the globe. I guessed that this orientation had an island right on the horizon, so that only one boundary point was visible, creating a singe point path for that island. I should probably fix my module so it doesn’t do that. However, it might be nice to have && and &&&& deal with this situation gracefully.
Gavin
\startMPpage path p[], q ; p1 = fullcircle scaled 3cm ; p2 = fullcircle scaled 2cm shifted (3cm,0) ; p3 = (3cm,2cm) ; q = for i = 1 upto 3 : p[i] && endfor cycle ; draw p1 withpen pencircle scaled 2pt withcolor .7 ; draw p2 withpen pencircle scaled 2pt withcolor .7 ; draw p3 withpen pencircle scaled 2pt withcolor .7 ; draw q withcolor red ; eofill q withcolor 0.9 ; draw fullcircle scaled 6cm shifted (1.25cm,0) ; \stopMPpage
Not beautiful, but this seems to do what you want in this particular case: \startMPpage path p[], q ; p1 = fullcircle scaled 3cm ; p2 = fullcircle scaled 2cm shifted (3cm,0) ; p3 = (3cm,2cm) ; p4 = fullcircle ; q = p[1] for i = 2 upto 3: if (length(p[i]) == 0): &&& else: && fi p[i] endfor && cycle ; eofill q withcolor 0.9 ; draw p1 withpen pencircle scaled 2pt withcolor .7 ; draw p2 withpen pencircle scaled 2pt withcolor .7 ; draw p3 withpen pencircle scaled 2pt withcolor .7 ; draw q withcolor red ; draw fullcircle scaled 6cm shifted (1.25cm,0) ; \stopMPpage This gives q = p1 && p2 &&& p3 && cycle ; /Mikael
On 12/31/2023 8:06 AM, Mikael Sundqvist wrote:
\startMPpage path p[], q ; p1 = fullcircle scaled 3cm ; p2 = fullcircle scaled 2cm shifted (3cm,0) ; p3 = (3cm,2cm) ; p4 = fullcircle ; q = p[1] for i = 2 upto 3: if (length(p[i]) == 0): &&& else: && fi p[i] endfor && cycle ; eofill q withcolor 0.9 ; draw p1 withpen pencircle scaled 2pt withcolor .7 ; draw p2 withpen pencircle scaled 2pt withcolor .7 ; draw p3 withpen pencircle scaled 2pt withcolor .7 ; draw q withcolor red ; draw fullcircle scaled 6cm shifted (1.25cm,0) ; \stopMPpage maybe this is a bit more beautiful then
q = for i = 1 upto 3 : if length(p[i]) == 0 : % todo: a fast nolength (p[i]  p[i] shifted 5(eps,eps)) else: p[i] fi && endfor cycle ; (i'm not sure if we should change the implementation, probably not unless we have &&&&&  actually we could have proper keywords which makes it less clumsy. Or 'recycle' that does the ugly eps job when we have a zero length path but we can move that over the year boundary.) Hans  Hans Hagen  PRAGMA ADE Ridderstraat 27  8061 GH Hasselt  The Netherlands tel: 038 477 53 69  www.pragmaade.nl  www.pragmapod.nl 
Hi Hans and Mikael, Thanks for your solutions. I’m happy to discard paths that have no area, so I used: q = for i = 1 upto 3 : if (length(p[i]) > 1): p[i] && fi endfor cycle ; This worked in the MWE, but it didn’t solve my problem in the globes module. Something else must be happening there. I’ll keep looking. Gavin
Hello LuaMetaFun Fans, Can I use mp.inject.path in Lua to create a disconnected path in MetaPost? This is for my module that draws globes. I currently do something like this for drawing the continents. (This MWE has two triangular continents.) \startluacode continents = {} continents[1] = {{0,0}, {1,1}, {1,0}, cycle = true } continents[2] = {{0,1}, {1,0}, {1,1}, cycle = true } function mp.getglobepath(continentnum) mp.inject.path(continents[continentnum]) end \stopluacode \startMPpage path p[], q ; p1 = (lua.mp.getglobepath(1) scaled 1cm) ; p2 = (lua.mp.getglobepath(2) scaled 1cm) ; q = p1 && p2 && cycle ; draw p1 withpen pencircle scaled 2pt withcolor .7 ; draw p2 withpen pencircle scaled 2pt withcolor .7 ; fill q withcolor 0.9 ; draw q withcolor red ; \stopMPpage The path q has both of the continents, disconnected. I’d like to produce the two continents in Lua and pass them to MetaPost as a single disconnected path, using something like this: \startluacode continents = { {0,0}, {1,1}, {1,0}, — Change this to make a disconnected path! {0,1}, {1,0}, {1,1}, cycle = true } function mp.getglobepath() mp.inject.path(continents) end \stopluacode \startMPpage path p ; p = (lua.mp.getglobepath() scaled 1cm) ; fill p withcolor 0.9 ; draw p withcolor red ; \stopMPpage If I can make the path p disconnected, this would allow me to make exactly the path I want in Lua, before passing it to MetaPost, rather than passing lots of paths and connecting them in MetaPost with the mysterious (to me) && or &&&&. Thanks! Gavin
participants (3)

Gavin

Hans Hagen

Mikael Sundqvist