elm-pat

Create sewing patterns in your browser. Live Demo

Note, that this is in a very early development state. Nevertheless, I appreciate any questions or feedback. :) The remaining part of this document tries to explain some parts the architecture and how to extend it.

This project got a lot of inspiration and knowledge from Seamly2D and TauMeta, so you should definitely check these out, too!

What is this all about?

When constructing sewing patterns, one usually takes some measurments of the person the final clothes should be for (e.g. shoulder width, back width, leg length) and then follows some construction steps, like 'draw a point', 'draw a line from point A downwards of half the length of the back height', 'draw a line perpendicular to some other line at 2/3 of that line', etc..

Eventually, you should be able to feed this program all these construction steps, so that you only have to update the input measurements to adjust your sewing patterns.

How to add new Tools?

Suppose we want to implement a new tool which lets you add a new point on a line between two other points with a certain ratio. To do this, we need to define a state type for it like so:

type alias State =
    { start : Maybe Id
    , end : Maybe Id
    , ratio : Maybe Float
    }

We need a function which may return a new point, given this state and the global data, which includes for example the current cursor position on the canvas (if we decide to track it), all previously created points, or our set of variables:

point : Data -> State -> Maybe Point
point data state =
    ...


type alias Data =
    { store : PointStore
    , variables : Variables
    , viewPort : ViewPort
    , mousePosition : Maybe Position
    , focusedPoint : Maybe Id
    }

In this case, start and end have to be given (and we are able to compute their positions) but ratio is not necessary if we have a the current cursor position, in which case we can compute it using the positions of start and end.

We also need to provide a rendering function for the canvas:

svg : Callbacks msg -> (State -> msg) -> Data -> State -> Svg msg
svg callbacks updateState data state =
    ...


type alias Callbacks msg =
    { addPoint : Point -> msg
    , updateCursorPosition : Maybe Position -> msg
    , focusPoint : Maybe Id -> msg
    }

In svg you can use the function

svgUpdateMouse : Maybe msg -> (Maybe Position -> msg) -> Data -> Svg msg
svgUpdateMouse mouseClicked updateCursorPosition data =
    ...

to indicate that you want the cursor position be updated and to add a callback for mouse click events. In our example, we will only draw svgUpdateMouse when start and end are selected. The mouseClicked callback will then use the point function to create a new point.

To be able to select start or end by clicking on existing points in the canvas, you can use the function

svgSelectPoint : (Maybe Id -> msg) -> (Maybe Id -> msg) -> Data -> Svg msg
svgSelectPoint focusPoint selectPoint data =
    ...

The last bit is a view function which displays a form in which one can input the different values for the tool:

view : Callbacks msg -> (State -> msg) -> Data -> State -> Svg msg
view callbacks updateState data state =
    let
        updateRatio =
            (\newRatio -> { state | ratio = newRatio }) >> updateState

        ...
    in
    [ exprInput "ratio" state.ratio updateRatio
    , ...
    ]
        |> Tools.Common.view callbacks data state point

The module Tools.Common provides helper view functions for often used input elements.

Now you have to extend the Tool type in Editor and add the tool to allTools. The compiler errors should then guide you through the remaining necessary changes.

kirchner/elm-pat

elm-pat

What is this all about?

How to add new Tools?