* [NTG-context] Functional shading with MetaPost / MetaFun
@ 2025-01-09 21:44 Florent Michel
2025-01-10 0:17 ` [NTG-context] " Hans Hagen
0 siblings, 1 reply; 3+ messages in thread
From: Florent Michel @ 2025-01-09 21:44 UTC (permalink / raw)
To: mailing list for ConTeXt users
[-- Attachment #1.1: Type: text/plain, Size: 3517 bytes --]
Hi,
I was trying to see if I could use MetaFun / MetaPost as my main tool for
generating figures. I really like its close integration with ConTeXt,
speed, and expressivity making it, even for a beginner like me, a pleasure
to work with.
One difficulty I encountered is for generating 2D functional shadings. For
instance, I am not sure what is the best way to reproduce the following
pgfplots picture in MetaPost:
____________________________________________________________
\usemodule[pgfplots]
\pgfplotsset{width=10cm,compat=1.18}
\usepgfplotslibrary{patchplots}
\starttext
\startTEXpage
\starttikzpicture
\startaxis[
hide axis=true,
axis lines=none,hide axis,
enlargelimits=false,
scale only axis,
clip bounding box=upper bound,
clip=true,
]
\addplot[
patch,
shader=interp,
mesh/color input=explicit,
data cs=polar,
]
coordinates {
(90,4) [color=red]
(210,4) [color=green]
(-30,4) [color=blue]
};
\stopaxis
\stoptikzpicture
\stopTEXpage
\stoptext
____________________________________________________________
One idea is to draw a sequence of triangles, each with a linear gradient:
____________________________________________________________
\startMPpage
def LinearIntTriangle(expr pa, pb, pc, cola, colb, colc, n_iter) =
for i = n_iter step -1 until 1 :
path p;
x := i / n_iter;
y := (i - 0.5) / n_iter;
p := pa -- (pa + x * (pb - pa)) -- (pa + x * (pc - pa)) -- cycle;
sh := define_linear_shade(pa + y * (pb - pa), pa + y * (pc - pa),
(1 - y) * cola + y * colb, (1 - y) * cola +
y * colc);
fill p withshade sh;
endfor
enddef;
color cola, colb, colc;
cola := (0,1,0);
colb := (1,0,0);
colc := (0,0,1);
LinearIntTriangle((0,0), (50,50*(3**0.5)), (100,0), cola, colb, colc, 30);
\stopMPpage
____________________________________________________________
or to use a slight variation (decomposing the triangle in three so that the
color is ‘right’) along each edge:
____________________________________________________________
\startMPpage
def LinearIntTriangleB(expr pa, pb, pc, cola, colb, colc, n_iter) =
color centre_color;
centre_color := (cola + colb + colc) / 3;
LinearIntTriangle((pa + pb + pc) / 3, pa, pb, centre_color, cola, colb,
n_iter);
LinearIntTriangle((pa + pb + pc) / 3, pb, pc, centre_color, colb, colc,
n_iter);
LinearIntTriangle((pa + pb + pc) / 3, pc, pa, centre_color, colc, cola,
n_iter);
enddef;
color cola, colb, colc;
cola := (0,1,0);
colb := (1,0,0);
colc := (0,0,1);
LinearIntTriangleB((0,0), (50,50*(3**0.5)), (100,0), cola, colb, colc,
10);
\stopMPpage
____________________________________________________________
This approach gives ‘good enough’ results for large values of n_iter.
However, the size of the generated pdf is somewhat larger than the pgfplots
version: for instance, the first version above generates a 5KiB pdf versus
3.8KiB for the pgfplots version, while being somewhat less accurate.
Increasing n_iter to 100 gives a result which is (to my not-very-good eyes)
very close to the pgfplots version but the pdf size increases to about
20KiB, and takes significantly longer to render using MuPDF.
I'd be grateful if someone could point me to a better way to generate such
shadings in MetaFun / MetaPost.
Cheers,
Florent
[-- Attachment #1.2: Type: text/html, Size: 3870 bytes --]
[-- Attachment #2: Type: text/plain, Size: 511 bytes --]
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
webpage : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
archive : https://github.com/contextgarden/context
wiki : https://wiki.contextgarden.net
___________________________________________________________________________________
^ permalink raw reply [flat|nested] 3+ messages in thread
* [NTG-context] Re: Functional shading with MetaPost / MetaFun
2025-01-09 21:44 [NTG-context] Functional shading with MetaPost / MetaFun Florent Michel
@ 2025-01-10 0:17 ` Hans Hagen
2025-01-10 7:17 ` Florent Michel
0 siblings, 1 reply; 3+ messages in thread
From: Hans Hagen @ 2025-01-10 0:17 UTC (permalink / raw)
To: Florent Michel, mailing list for ConTeXt users
On 1/9/2025 10:44 PM, Florent Michel wrote:
> Hi,
>
> I was trying to see if I could use MetaFun / MetaPost as my main tool
> for generating figures. I really like its close integration with
> ConTeXt, speed, and expressivity making it, even for a beginner like me,
> a pleasure to work with.
>
> One difficulty I encountered is for generating 2D functional shadings.
> For instance, I am not sure what is the best way to reproduce the
> following pgfplots picture in MetaPost:
>
> ____________________________________________________________
> \usemodule[pgfplots]
> \pgfplotsset{width=10cm,compat=1.18}
> \usepgfplotslibrary{patchplots}
>
> \starttext
>
> \startTEXpage
> \starttikzpicture
> \startaxis[
> hide axis=true,
> axis lines=none,hide axis,
> enlargelimits=false,
> scale only axis,
> clip bounding box=upper bound,
> clip=true,
> ]
> \addplot[
> patch,
> shader=interp,
> mesh/color input=explicit,
> data cs=polar,
> ]
> coordinates {
> (90,4) [color=red]
> (210,4) [color=green]
> (-30,4) [color=blue]
> };
> \stopaxis
> \stoptikzpicture
> \stopTEXpage
> \stoptext
> ____________________________________________________________
>
> One idea is to draw a sequence of triangles, each with a linear gradient:
> ____________________________________________________________
> \startMPpage
> def LinearIntTriangle(expr pa, pb, pc, cola, colb, colc, n_iter) =
> for i = n_iter step -1 until 1 :
> path p;
> x := i / n_iter;
> y := (i - 0.5) / n_iter;
> p := pa -- (pa + x * (pb - pa)) -- (pa + x * (pc - pa)) -- cycle;
> sh := define_linear_shade(pa + y * (pb - pa), pa + y * (pc - pa),
> (1 - y) * cola + y * colb, (1 - y) *
> cola + y * colc);
> fill p withshade sh;
> endfor
> enddef;
>
> color cola, colb, colc;
> cola := (0,1,0);
> colb := (1,0,0);
> colc := (0,0,1);
>
> LinearIntTriangle((0,0), (50,50*(3**0.5)), (100,0), cola, colb, colc,
> 30);
> \stopMPpage
> ____________________________________________________________
>
> or to use a slight variation (decomposing the triangle in three so that
> the color is ‘right’) along each edge:
> ____________________________________________________________
> \startMPpage
> def LinearIntTriangleB(expr pa, pb, pc, cola, colb, colc, n_iter) =
> color centre_color;
> centre_color := (cola + colb + colc) / 3;
> LinearIntTriangle((pa + pb + pc) / 3, pa, pb, centre_color, cola,
> colb, n_iter);
> LinearIntTriangle((pa + pb + pc) / 3, pb, pc, centre_color, colb,
> colc, n_iter);
> LinearIntTriangle((pa + pb + pc) / 3, pc, pa, centre_color, colc,
> cola, n_iter);
> enddef;
>
> color cola, colb, colc;
> cola := (0,1,0);
> colb := (1,0,0);
> colc := (0,0,1);
>
> LinearIntTriangleB((0,0), (50,50*(3**0.5)), (100,0), cola, colb,
> colc, 10);
> \stopMPpage
> ____________________________________________________________
>
> This approach gives ‘good enough’ results for large values of n_iter.
> However, the size of the generated pdf is somewhat larger than the
> pgfplots version: for instance, the first version above generates a 5KiB
> pdf versus 3.8KiB for the pgfplots version, while being somewhat less
> accurate. Increasing n_iter to 100 gives a result which is (to my not-
> very-good eyes) very close to the pgfplots version but the pdf size
> increases to about 20KiB, and takes significantly longer to render using
> MuPDF.
>
> I'd be grateful if someone could point me to a better way to generate
> such shadings in MetaFun / MetaPost.
these things can often be found in the test suite
\startMPpage
fill unittriangle rotated 90 xyscaled (200,100)
withshademethod "linear"
withshadecenteronefraction (0,1)
withshadecentertwofraction (0,0)
withshadestep (
withshadefraction 0
withshadecolors (green, green)
)
withshadestep (
withshadefraction 0.75
withshadecolors (blue, green)
)
withshadestep (
withshadefraction 0.25
withshadecolors (green, blue)
)
withshadestep (
withshadefraction 1
withshadecolors (green, red)
)
;
\stopMPpage
-----------------------------------------------------------------
Hans Hagen | PRAGMA ADE
Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
webpage : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
archive : https://github.com/contextgarden/context
wiki : https://wiki.contextgarden.net
___________________________________________________________________________________
^ permalink raw reply [flat|nested] 3+ messages in thread
* [NTG-context] Re: Functional shading with MetaPost / MetaFun
2025-01-10 0:17 ` [NTG-context] " Hans Hagen
@ 2025-01-10 7:17 ` Florent Michel
0 siblings, 0 replies; 3+ messages in thread
From: Florent Michel @ 2025-01-10 7:17 UTC (permalink / raw)
To: Hans Hagen; +Cc: mailing list for ConTeXt users
[-- Attachment #1.1: Type: text/plain, Size: 6018 bytes --]
Thank you very much Hans for this solution! Very interesting!
One thing I'm still not understanding (but maybe I'm missing something
obvious) is how to reproduce the ‘2D gradient’ effect of the PGFplots
version, where one corner is red, one is green, and one is red with the
shading inside the triangle interpolating smoothly between the three
colours (apologies if my previous email was not clear on that!). Running
the code you sent, I get a change of colour in the vertical direction only
(it looks nice, though!). Would you know if there is a way to achieve a
similar ‘2D gradient’ effect in MetaPost?
Here are two screenshots to whos the difference: https://imgur.com/a/SlJ4BiE
Thank you also for pointing me to the test suite! It seems to have many
useful examples!
Cheers,
Florent
On Fri, Jan 10, 2025, 00:17 Hans Hagen <j.hagen@xs4all.nl> wrote:
> On 1/9/2025 10:44 PM, Florent Michel wrote:
> > Hi,
> >
> > I was trying to see if I could use MetaFun / MetaPost as my main tool
> > for generating figures. I really like its close integration with
> > ConTeXt, speed, and expressivity making it, even for a beginner like me,
> > a pleasure to work with.
> >
> > One difficulty I encountered is for generating 2D functional shadings.
> > For instance, I am not sure what is the best way to reproduce the
> > following pgfplots picture in MetaPost:
> >
> > ____________________________________________________________
> > \usemodule[pgfplots]
> > \pgfplotsset{width=10cm,compat=1.18}
> > \usepgfplotslibrary{patchplots}
> >
> > \starttext
> >
> > \startTEXpage
> > \starttikzpicture
> > \startaxis[
> > hide axis=true,
> > axis lines=none,hide axis,
> > enlargelimits=false,
> > scale only axis,
> > clip bounding box=upper bound,
> > clip=true,
> > ]
> > \addplot[
> > patch,
> > shader=interp,
> > mesh/color input=explicit,
> > data cs=polar,
> > ]
> > coordinates {
> > (90,4) [color=red]
> > (210,4) [color=green]
> > (-30,4) [color=blue]
> > };
> > \stopaxis
> > \stoptikzpicture
> > \stopTEXpage
> > \stoptext
> > ____________________________________________________________
> >
> > One idea is to draw a sequence of triangles, each with a linear gradient:
> > ____________________________________________________________
> > \startMPpage
> > def LinearIntTriangle(expr pa, pb, pc, cola, colb, colc, n_iter) =
> > for i = n_iter step -1 until 1 :
> > path p;
> > x := i / n_iter;
> > y := (i - 0.5) / n_iter;
> > p := pa -- (pa + x * (pb - pa)) -- (pa + x * (pc - pa)) -- cycle;
> > sh := define_linear_shade(pa + y * (pb - pa), pa + y * (pc - pa),
> > (1 - y) * cola + y * colb, (1 - y) *
> > cola + y * colc);
> > fill p withshade sh;
> > endfor
> > enddef;
> >
> > color cola, colb, colc;
> > cola := (0,1,0);
> > colb := (1,0,0);
> > colc := (0,0,1);
> >
> > LinearIntTriangle((0,0), (50,50*(3**0.5)), (100,0), cola, colb, colc,
> > 30);
> > \stopMPpage
> > ____________________________________________________________
> >
> > or to use a slight variation (decomposing the triangle in three so that
> > the color is ‘right’) along each edge:
> > ____________________________________________________________
> > \startMPpage
> > def LinearIntTriangleB(expr pa, pb, pc, cola, colb, colc, n_iter) =
> > color centre_color;
> > centre_color := (cola + colb + colc) / 3;
> > LinearIntTriangle((pa + pb + pc) / 3, pa, pb, centre_color, cola,
> > colb, n_iter);
> > LinearIntTriangle((pa + pb + pc) / 3, pb, pc, centre_color, colb,
> > colc, n_iter);
> > LinearIntTriangle((pa + pb + pc) / 3, pc, pa, centre_color, colc,
> > cola, n_iter);
> > enddef;
> >
> > color cola, colb, colc;
> > cola := (0,1,0);
> > colb := (1,0,0);
> > colc := (0,0,1);
> >
> > LinearIntTriangleB((0,0), (50,50*(3**0.5)), (100,0), cola, colb,
> > colc, 10);
> > \stopMPpage
> > ____________________________________________________________
> >
> > This approach gives ‘good enough’ results for large values of n_iter.
> > However, the size of the generated pdf is somewhat larger than the
> > pgfplots version: for instance, the first version above generates a 5KiB
> > pdf versus 3.8KiB for the pgfplots version, while being somewhat less
> > accurate. Increasing n_iter to 100 gives a result which is (to my not-
> > very-good eyes) very close to the pgfplots version but the pdf size
> > increases to about 20KiB, and takes significantly longer to render using
> > MuPDF.
> >
> > I'd be grateful if someone could point me to a better way to generate
> > such shadings in MetaFun / MetaPost.
>
> these things can often be found in the test suite
>
> \startMPpage
> fill unittriangle rotated 90 xyscaled (200,100)
> withshademethod "linear"
> withshadecenteronefraction (0,1)
> withshadecentertwofraction (0,0)
> withshadestep (
> withshadefraction 0
> withshadecolors (green, green)
> )
> withshadestep (
> withshadefraction 0.75
> withshadecolors (blue, green)
> )
> withshadestep (
> withshadefraction 0.25
> withshadecolors (green, blue)
> )
> withshadestep (
> withshadefraction 1
> withshadecolors (green, red)
> )
> ;
> \stopMPpage
>
>
> -----------------------------------------------------------------
> Hans Hagen | PRAGMA ADE
> Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
> tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------
>
[-- Attachment #1.2: Type: text/html, Size: 7534 bytes --]
[-- Attachment #2: Type: text/plain, Size: 511 bytes --]
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nl
webpage : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
archive : https://github.com/contextgarden/context
wiki : https://wiki.contextgarden.net
___________________________________________________________________________________
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2025-01-10 7:19 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2025-01-09 21:44 [NTG-context] Functional shading with MetaPost / MetaFun Florent Michel
2025-01-10 0:17 ` [NTG-context] " Hans Hagen
2025-01-10 7:17 ` Florent Michel
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).