Btukfyl

I really like the facility in ChemFig to choose the bond angle in 45 degree increments by specifying an integer, instead of the angle directly: chemfig{-[1]}. Right now, I'm drawing a bunch of hydrocarbon molecules, and I think a 30 degree increment on the bond angle looks better. Of course, I can specify each angle using the [:angle] syntax, but that's too much typing! Is there any comparable shortcut for 30 degree angles?

documentclass{standalone}

usepackage{chemfig}

begin{document}

chemfig{-[:30]-[:330]-[:30]-[:330]}

end{document}

The idea is to create a new macro setangleincrement which allow to set the increment of the angle when [<number>] follows a bond. It could be a new feature for the next version...

documentclass{article}

usepackage{chemfig}

makeatletter

CF@defsetangleincrement{defCF@angle@increment}

setangleincrement{45}% default value

defCF@set@bondangle#1#2{% le code de la direction est contenu dans #1, en sortie, #2 contient l'angle

    ifx@empty#1@empty%

        let#2CF@default@angle

    else

        if:expandafternoexpand@car#1@nil

            if:expandafterexpandafterexpandafternoexpandexpandafter@car@gobble#1@nil

                pgfmathsetmacro#2{CF@previous@angle+expandafter@gobble@gobble#1}%

            else

                expandafterdefexpandafter#2expandafter{@gobble#1}%

            fi

        else

            pgfmathsetmacro#2{#1*CF@angle@increment}%

        fi% puis normalise l'angle entre 0 et 360

        ifdimifdim#2pt<z@-fi#2pt>360pt pgfmathsetmacro #2{#2-360*floor(#2/360)}fi% si |#2|>360

    fi

}

makeatother

begin{document}

45 degres increment: chemfig{-[9]-[-1]-[1]-[-1]}



setangleincrement{30}

30 degres increment: chemfig{-[1]-[-1]-[1]-[-1]}

end{document}

You can use setchemfig.

documentclass{article}

usepackage{chemfig}

begin{document}

setchemfig{angle increment=30}

chemfig{-[1]-[-1]-[1]-[-1]-[1]-[-1]-[1]}

end{document}

Depending on the use case I'd use submols:

documentclass{standalone}

usepackage{chemfig}

definesubmol{r}{-[::-60]}

definesubmol{l}{-[::60]}

begin{document}

chemfig{[:30]-!r!l!r!l}

end{document}

Well, there is no built-in way to use such a shortcut. But, we can hack one together by re-defining the code that processes the bond angle specification.
(PS I'm rather new at doing this sort of thing, so improvement suggestions are welcome!)

Somewhat arbitrarily, I'll choose letters a through l (lowercase ell) to represent the angles 0 through 330 degrees. Then, we just need to add some code to the bottom of the macro where the processing of the integer specifications takes place to process the letters instead of numbers:

defCF@set@bondangle#1#2{

    ifx@empty#1@empty%

        let#2CF@default@angle

    else

        if

             ...% In the code I've removed, it reads the explicit angle specification

        else % Here is the new code

            ifnum0<0#1relax% First check if the input is an integer or a letter

                ifnum#1>7% If an integer, process as before. This code is unchanged

                    pgfmathparse{#1-floor(#1/8)*8}

                    ifdimpgfmathresult pt<z@pgfmathparse{pgfmathresult+8}fi

                    edef#2{ifcaseexpandafterCF@int@partpgfmathresult@nil0or45or90or135or180or225or270or315else-1fi}

                else

                    edef#2{ifcase#1 0or45or90or135or180or225or270or315else-1fi}%

                fi

            else% Otherwise, process the letter into an integer and assign the proper angle

                edef#2{ifcasenumexpr`#1 - `arelax 0or30or60or90or120or150or180or210or240or270or300or330else-1fi}%

            fi%

        fi

    fi

}

Note that only letters a through l are supported, and this can probably break in a number of unforeseen ways, including (I think) negative integer inputs (but those didn't work in the original implementation anyways). The line to check whether the input is an integer or letter is from here: How to check if the value of a parameter is a number? (see egreg's answer), and the code to check the case containing a letter was suggested by David Carlisle.

MWE:

documentclass{standalone}

usepackage{chemfig}

makeatletter

defCF@set@bondangle#1#2{% le code de la direction est contenu dans #1, en sortie, #2 contient l'angle

    ifx@empty#1@empty%

        let#2CF@default@angle

    else

        if:expandafternoexpand@car#1@nil

            if:expandafterexpandafterexpandafternoexpandexpandafter@car@gobble#1@nil

                pgfmathparse{CF@previous@angle+expandafter@gobble@gobble#1}%

                let#2pgfmathresult

            else

                expandafterdefexpandafter#2expandafter{@gobble#1}%

            fi% puis normalise l'angle entre 0 et 360

            ifdimifdim#2pt<z@-fi#2pt>360pt % si |#2|>360

                pgfmathparse{#2-360*floor(#2/360)}%

                ifdimpgfmathresult pt<z@pgfmathparse{pgfmathresult+360}fi

                let#2pgfmathresult

            else

                ifdim#2pt<z@

                    pgfmathparse{#2+360}%

                    let#2pgfmathresult

                fi

            fi

        else

            ifnum0<0#1relax%

                ifnum#1>7

                    pgfmathparse{#1-floor(#1/8)*8}%

                    ifdimpgfmathresult pt<z@pgfmathparse{pgfmathresult+8}fi

                    edef#2{ifcaseexpandafterCF@int@partpgfmathresult@nil0or45or90or135or180or225or270or315else-1fi}

                else

                    edef#2{ifcase#1 0or45or90or135or180or225or270or315else-1fi}%

                fi

            else

                edef#2{ifcasenumexpr`#1 - `arelax 0or30or60or90or120or150or180or210or240or270or300or330else-1fi}%

            fi%

        fi

    fi

}

makeatother



begin{document}

chemfig{-[:30]-[l]-[b]-[:330]}

end{document}