Entry-level MetaPost: On the grid
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1. we ve built up follows and the output without the background grid is in fig 10 begin full example numeric u u 5cm fill fullcircle scaled 1 5u withcolor red fill fullcircle scaled 1 5u shifted 3u 5u withcolor blue fill fullcircle scaled 1 5u shifted 4ut 1 8u 3 25u withcolor green for i 6u step 1 2u until 10u draw fullcircle scaled 1 5u shifted 8u i withcolor red endfor for i 0 step 1 2u until 3u draw fullcircle scaled 1 5u shifted 2 i i 9u withcolor green endfor Define the black object picture curvy curvy image fill 5u iu 7u 5u 7 5u 5u 8u 3u 9u 3u 7u 1 2u cycle Draw the black object draw curvy Draw bounding box around the object draw llcorner curvy lrcorner curvy urcorner curvy ulcorner curvy cycle withcolor blue Add dot at lrcorner of object bounding box fill fullcircle scaled 1 5u shifted lrcorner curvy withcolor 0 5blue Add red dots at object turning points fill fullcircle scaled 1 10u shifted 5u 1u withcolor red fill fullcircle scaled 1 10u shifted 7u 5u withcolor red fill fullcircle scaled 1 10u shifted 7 5u 5u withcolor red fill fullcircle scaled 1 10u shifted 8u 3u withcolor red fill fullcircle scaled 1 10u shifted 9u 3u withcolor red fill fullcircle scaled 1 10u shifted 7u 1 2u withcolor red Add whitespace setbounds currentpictu2. 10 1 height width withcolor 8white J3 draw grid withpen pencircle scaled 1 20 I put the grid code in the beginning of my Meta Post file s and thus it gets drawn first and ends up in the background behind all other elements The numbers are standard labels set with the label labelname x y command For example label 1 1 4u 1u 2 3 Further reading Metafun manual http www pragma ade com general manuals metafun p pdf Many examples work in plain MetaPost More graphical than e g the user s manual MetaPost user s manual http www tug org docs metapost mpman pdf MetaPost a very brief tutorial http www ursoswald ch metapost tutorial html A more traditional approach to MetaPost Click on filenames to get the code MetaPost home page http www tug org metapost Lots of links to other tutorials examples articles packages and more Mari Voipio mari dot voipio at lucet dot fi http www lucet fi
3. TUGboat Volume 34 2013 No 1 Entry level MetaPost On the grid Mari Voipio 1 Running MetaPost The basic method for running MetaPost is to create a file with extension mp and run MetaPost directly on the command line mpost yourfile mp In the mp file the code for making graphics is enclosed within beginfig endfig the result is a PostScript file The file extension is the figure number With this example the output would be a file yourfile 1 beginfig 1 Draw a line draw icm 2cm 3cm 5cm endfig end If you add outputformat svg at the very beginning of the file the output will be in SVG format However the resulting file will still be named yourfile 1 depending on your system you may have to rename it to yourfile svg for it to be recognized Another method available in any decent TEX distribution is to run MetaPost inside a ConTEXt file I am a ConTEXt user so I find it handiest to do it this way The file extension is the usual tex and the MetaPost code the same MetaPost code as when running standalone is enclosed inside startMPpage stopMPpage I run my files within an editor with a menu command Typeset but you can also typeset the file on the command line with context yourfile tex startMPpage Draw a line draw icm 2cm 3cm 5cm stopMPpage The output from ConTEXt is by default a PDF file yourfile pdf Graphics code can be included in any tex file you ca
4. e using MetaPost s default unit the big point Try the above mentioned trick of defining a unit u to suit your taste or use units with your coordinates In the beginning I found it easiest to think on a millimeter grid so I defined lines with e g draw 8mm 20mm 10mm 40mm Mari Voipio TUGboat Volume 34 2013 No 1 MetaPost draws items in the order they are defined If your file compiles but you only get some of the objects the missing ones may be underneath everything else Our examples above are carefully spread out so they don t overlap but if you play with the coordinates you may encounter this feature If you draw several items at the same spot the first highest up in the code is at the bottom in the drawing and the last in the file is on top in the final graphic it may help to think of the lines and objects as pieces of paper piled up on top of each other so the last piece ends up on top of everything else 2 2 Drawing the background grid I used Metafun to draw the gray grid in the illus trations above Metafun comes with ConTEXt so if you have ConTEXt your TEX installation already includes it Besides a plain grid Metafun also sup ports creating slanted or logarithmic grids see pages 213 214 in the Metafun manual First we define the grid then draw it picture grid grid image width 10 height 10 draw vlingrid 0 10 1 width height withcolor 8white draw hlingrid 0
5. n have text and MP code in one and the same ConTRXt file 2 Building up a graphic To draw anything with MetaPost you have to have some kind of idea of where your drawings end up and why Everything is related to a base grid it doesn t usually show but in our examples here I ve put a grid in the background to help you figure out how to place objects in MetaPost A blank grid is shown in fig 1 We ll see how to draw the grid itself later The MP grid extends to all directions e g coor dinates 1 2 1 2 1 2 and 1 2 all exist However I find it easiest to stay on the positive side when coding a drawing or an element objects can be easily shifted later to their proper locations 17 10 o 1 2 3 4 5 6 7 8 9 10 Figure 1 MetaPost drawings are made on a grid 10 0 1 2 3 4 5 6 7 8 9 10 Figure 2 A red dot at the origin The basic unit of MetaPost is a big point bp and that one is tiny 72 bp lin There are several ways of changing the scale in the examples below we ll use a user defined unit u That way we only have to change u if we want to adapt the drawing to a different size scale Here we ll define the unit u at the beginning of the MetaPost file to fit TUGboat numeric u u 5cm As a first example let s draw a small red dot a filled circle at the origin The output is in fig 2 If we had nothing else in the picture we d get a red dot in the middle
6. of the page with some white around and that s it our dot here isn t in the middle because of the grid in the background Set the scale numeric u u 5cm Draw a red dot at origin fill fullcircle scaled 1 5u withcolor red Add whitespace around the drawing Entry level MetaPost On the grid 18 10 o 1 2 3 4 5 6 7 8 9 10 Figure 3 Add a blue dot at 3 5 10 o 1 2 3 4 5 6 7 8 9 10 Figure 4 Add a green dot off the integer grid setbounds currentpicture to boundingbox currentpicture enlarged 1 2u Next let s add another dot in blue at 3 5 fill fullcircle scaled 1 5u shifted 3u 5u withcolor blue This command goes after the previous fill above the setbounds command as do our subsequent ad ditions Output in fig 3 We don t have to use whole numbers MetaPost is just as handy with decimals and fractions fig 4 fill fullcircle scaled 1 5u shifted 4ut1 8u 3 25u withcolor green When something is repeated at regular intervals a loop can be used fig 5 for i 6u step 1 2u until 10u draw fullcircle scaled 1 5u shifted 8u i withcolor red endfor We can change both coordinates inside one loop for i 0 step 1 2u until 3u Mari Voipio TUGboat Volume 34 2013 No 1 10 0 0 0 0 0o60 0 1 2 3 4 5 6 7 8 9 10 Figure 5 Add a vertical series of red dots with a loop 10 O 9 8 0 6 6 8 0 1 2 3 4 5 6 7 8 9 10 Figure 6 Add a diagonal
7. re Entry level MetaPost On the grid 20 oo oo 0000 Figure 10 The complete example figure without the background grid to boundingbox currentpicture enlarged 1 2cm Scale up to be readable currentpicture currentpicture xsized 6cm end full example 2 1 Troubleshooting With MetaPost as well as with TEX I ve found that it is a good idea to compile typeset the file fairly frequently especially when doing something for the first time I carefully grow my MetaPost graphics stage by stage very much like the examples above If my file suddenly stops working I comment out the newest lines with and recompile to check that I haven t say accidentally deleted a semicolon in the older code and then proceed to debug the newest code If your file doesn t compile the first thing to look for is an omission a missing semicolon at the end of a command a missing endfig stopMPpage missing parentheses If the semicolon on the last line is missing the file will compile but only until something is added after that line then it fails If you draw something with the fill command the item to fill must be a closed path either a line curve closed with cycle or a circle or square e g fullcircle If you try to fill a non cyclical path your file won t compile because MetaPost hangs at the impossible command If your drawing is tiny and needs lots of zooming to be visible you may b
8. series of green dots draw fullcircle scaled 1 5u shifted 2 i i 9u withcolor green endfor Lines and objects are drawn by connecting two or more sets of coordinates Either a straight line specified with or a curved line is drawn between the given coordinates A line is turned into a closed object with the final command cycle Only a closed object can be filled with colour See fig 7 fill 5u 1u 7u 5u 7 5u 5u 8u 3u 9u 3u 7u 1 2u cycle In the next picture fig 8 these curve coordi nates have been marked with small red dots If you are not familiar with Bezier curves the behaviour of the curved lines can be surprising A line or an object always has a bounding box a rectangular frame MetaPost knows where the corners of the bounding box are in fig 9 the box is drawn as a line from corner to corner on the black object red dots are added later and the dark blue TUGboat Volume 34 2013 No 1 10 O 0 e 0 0 0 1 2 3 4 5 6 7 8 T Figure 7 Add a filled shape which uses both curves and lines 10 O 0 10 0 0 12 3 4 5 6 7 8 U 10 Figure 8 Show the curve coordinates with red dots 10 Oo 0 0 9 9 0 0 0 0 1 2 3 4 5 6 7 8 9 10 Figure 9 Outline the shape s bounding box with a dot at its lower right 19 dot is placed on the lower right corner 1rcorner of the black object All of the code
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