[NTG-context] Re: MetaPost behaviour differs between standalone and \startreusableMPgraphic

On 2/19/2025 4:31 AM, Gavin via ntg-context wrote:

Hi Pavneet,

I recommend avoiding the mod function. Just draw the two grids (major and minor) each with their own spacing and pen.

Indeed. Don't rely on rounding etc because especially in loops (until) you can easily get one step more or less. This is why we often see these within 'eps' range tests. My guess is that Pavneet runs mp stand alone in scaled mode while context by default uses double mode. For them to run the same one can do. One can try mtxrun --script metapost foo.mp instead.

I whole heatedly support converting TikZ to MetaPost!

- Gavin

\startreusableMPgraphic{graph} minor=2mm; % Minor lines, each every 2mm major=8mm; % Major lines, each every 4mm

z1 = (0,0); % lower left corner % z2 = (2.75in,4.25in)-z1; % upper right corner z2 = (2.75in,4.25in)-z1;% upper right corner

path v, h; v := z1--(x1,y2); % vertical line h := z1--(x2,y1); % horizontal line

% Use light gray drawoptions(withcolor .4white);

% Draw the minor grid with the very thin pen pickup pencircle scaled 0.1; for i=minor step minor until (x2-x1): draw v xshifted i; endfor; for i=minor step minor until (y2-y1): draw h yshifted i; endfor;

% Draw the major grid with the thicker pen pickup pencircle scaled 0.3; for i=major step major until (x2-x1): draw v xshifted i; endfor; for i=major step major until (y2-y1): draw h yshifted i; endfor;

\stopreusableMPgraphic

...

On Feb 18, 2025, at 3:28 PM, Pavneet Arora via ntg-context wrote:

I am in the process of converting a bunch of old TikZ notepaper templates to native ConTeXt and MetaPost. This is a part of a project to generate notebooks with documentation data and then blank pages appended to fill out full sheets, and then collated in a particular order for trimming and binding.

As such I rely on Imposition. I am having issues with the various techniques of trying to duplicate a MP graphic across the pages using \[start|stop]MPcode \[start|stop]useMPgraphic, etc. But that is a discussion for another time.

The method that I found to work was to use \[start|stop]reusableMPgraphic along with overlays

I am still struggling with some MetaPost code that works fine in standalone but not when included in a ConTeXt document.

With standalone MP, we get thicker lines on major increments as expected. When the same code is included in a ConTeXt document the thicker lines are only drawn up a certain number and then stop --- presumably the mod function returning a non-zero result when it really shouldn't?

Here are the MWEs:

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ConTeXt % Paper size and layout {{{2 \definepapersize | [PocketPage] | [width=2.75in,height=4.25in]

\setuppapersize[PocketPage][letter,landscape] % }}}2

% MetaPost template for graph paper for pocket sized notebook (2.75" W x % 4.25in H). {{{2

\startreusableMPgraphic{graph} minor=2mm;| | % Minor lines, each every 2mm major=8mm;| | % Major lines, each every 4mm ┆ ┆ ┆ ┆ % major must be a multiple of minor

z1 = (0,0);| % lower left corner % z2 = (2.75in,4.25in)-z1;| % upper right corner z2 = (2.75in,4.25in)-z1;|% upper right corner

% Use the very thin pen pickup pencircle scaled 0.1;

% Draw the vertical lines for i=minor step minor until (y2-y1): ┆ if (i mod major)=0: ┆ ┆ pickup pencircle scaled 0.3; ┆ fi; ┆ draw (z1 shifted (0,i))--((x2,y1) shifted (0,i)) withcolor .4white; ┆ if (i mod major)=0: ┆ ┆ pickup pencircle scaled 0.1; ┆ fi; endfor;

% Draw the horizonal lines for i=minor step minor until (x2-x1): ┆ if (i mod major)=0: ┆ ┆ pickup pencircle scaled 0.3; ┆ fi; ┆ draw ( z1--(x1,y2) ) shifted (i,0) withcolor .4white; ┆ if (i mod major)=0: ┆ ┆ pickup pencircle scaled 0.1; ┆ fi; endfor;

\stopreusableMPgraphic

\defineoverlay[OLgraph][\useMPgraphic{graph}]

\setupbackgrounds[page][background=OLgraph] % }}}2

\starttext

hello.

\stoptext

<<<

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Standalone MP beginfig(1)

margin=0mm; % Margin of the graph paper minor=2mm; % Minor lines, each every 1mm major=8mm; % Major lines, each every 10mm % major must be a multiple of minor

z1 = (margin,margin); % lower left corner z2 = (2.75in,4.25in)-z1; % upper right corner

% % Use the thick pen first % pickup pencircle scaled 0.5;

% % Draw the frame % draw z1--(x1,y2)--z2--(x2,y1)--cycle withcolor .5white;

% Use the very thin pen pickup pencircle scaled 0.1;

% Draw the vertical lines for i=minor step minor until (y2-y1-minor): if (i mod major)=0: pickup pencircle scaled 0.3; fi; draw (z1 shifted (0,i))--((x2,y1) shifted (0,i)) withcolor .4white; if (i mod major)=0: pickup pencircle scaled 0.1; fi; endfor;

% Draw the horizonal lines for i=minor step minor until (x2-x1-minor): if (i mod major)=0: pickup pencircle scaled 0.3; fi; draw ( z1--(x1,y2) ) shifted (i,0) withcolor .4white; if (i mod major)=0: pickup pencircle scaled 0.1; fi; endfor;

endfig; end;

<<<

advTHANKance

-- Pavneet Arora m: +1 647-406-6843 Waroc Informatik e: pavneet_arora@waroc.com ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki!

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