I thought I'd open an issue for this as it's marked as TODO in the code anyway and I have started working on this seperately.

If you do a cabal run in my project though you can see that the second property won't pass quickcheck. Sometimes this is due to floating point errors (which seem to exceed ieee754) but sometimes there are NaNs in the result which indicates there is no solution although I think I scale rx,ry as described.

Just wondering if you had any ideas and also if you would be interested to use my implementation if I get it to work.

Some initial steps have been done, but it is not finished

When reading in an SVG with loadImageEmbedded the width and height of the SVG seem to be ignored. When reading an SVG and then asking the diagrams library for the width and height, the reported numbers seem to be the bounding box of the objects in the SVG, not the size of the full image. Is this a bug or is this on purpose?

On a related note, after upgrading to GHC 8 my diagrams look a bit different, and I think that it is related to the width/height of the svg components being reported differently, but I am not 100% sure.

This is in my opinion an issue in attoparsec.

I have the following path:

<!-- https://fontawesome.com/icons/flag?style=solid CC-BY -->
<path fill="Indigo" d="M349.565 98.783C295.978 98.783 251.721 64 184.348 64c-24.955 0-47.309 4.384-68.045 12.013a55.947 55.947 0 0 0 3.586-23.562C118.117 24.015 94.806 1.206 66.338.048 34.345-1.254 8 24.296 8 56c0 19.026 9.497 35.825 24 45.945V488c0 13.255 10.745 24 24 24h16c13.255 0 24-10.745 24-24v-94.4c28.311-12.064 63.582-22.122 114.435-22.122 53.588 0 97.844 34.783 165.217 34.783 48.169 0 86.667-16.294 122.505-40.858C506.84 359.452 512 349.571 512 339.045v-243.1c0-23.393-24.269-38.87-45.485-29.016-34.338 15.948-76.454 31.854-116.95 31.854z"></path>

Firefox renders it like this:

But with this library I get this:

It looks like it stops at "C118.117 24.015 94.806 1.206 66.338.048". According to the spec, this is actually valid and should be parsed as 66.338 0.048! 😮

Similarly, for the string "M 0.6.5", the first coordinate of the "moveto" consumes the characters "0.6" and stops upon encountering the second decimal point because the production of a "coordinate" only allows one decimal point. The result is that the first coordinate will be "0.6" and the second coordinate will be ".5".

This is something that a lot of SVG renderers have not implemented. But it is used in some SVGs. Luckily I can learn a lot from svg-tree, because it's implemented there.

Some SVG images use CSS to set colors. Apart from this haven't seen more advanced uses of CSS. A minimal CSS support was added. But a complete implementation of CSS would of course be nice. Maybe this becomes a topic when we render HTML pages.

Using the below function on this test.svg.

pathToPoints :: String -> [[(Double,Double)]]
pathToPoints = map (map unp2) . concat . (map pathVertices) . commandsToTrails . commands . Just . pack

I get something that looks like this.

With the old SVGPath I get something that looks like this.

Maybe I shouldn't be using pathVertices?

The -tag references tags (mostly from inside the -tag) to reuse objects. Viewbox and preserveAspectRatio from the referenced object have to be considered

The main part of the example is:

main = do
   diagramFromSVG  <- readSVGFile "svgs/web.svg"
   mainWith $ diagramFromSVG

The error is:

Main.hs:12:22: error:
    • Couldn't match type ‘N b0’ with ‘Place’
        arising from a use of ‘readSVGFile’
      The type variable ‘b0’ is ambiguous
    • In a stmt of a 'do' block:
        diagramFromSVG <- readSVGFile "svgs/web.svg"
      In the expression:
        do diagramFromSVG <- readSVGFile "svgs/web.svg"
           mainWith $ diagramFromSVG
      In an equation for ‘main’:
          main
            = do diagramFromSVG <- readSVGFile "svgs/web.svg"
                 mainWith $ diagramFromSVG

The function readSVGFilereturns an Either String (Diagram B) but
the function mainWith expects a plain Diagram B.

A working example is:

{-# LANGUAGE OverloadedStrings, ScopedTypeVariables #-}

module Main where
import Diagrams.SVG.ReadSVG
import Diagrams.Prelude
import Diagrams.Backend.SVG.CmdLine
import System.Environment
import Filesystem.Path.CurrentOS
import Diagrams.SVG.Attributes (PreserveAR(..), AlignSVG(..), Place(..), MeetOrSlice(..))

main = do
   diagramFromSVG :: Either String (Diagram B) <- readSVGFile "svgs/web.svg"
   case diagramFromSVG of
    Left msg      -> error ("readSVGFile returned " <> msg)
    Right diagram -> mainWith $ diagram

It needs a type hint for diagramFromSVG.

Examples from the documentation of a library should work without any changes.

Verions used:

• GHC: The Glorious Glasgow Haskell Compilation System, version 9.2.2
• diagrams-input: 0.1

Currently one has to manually delete the xmlns attribute to parse the SVG file. It seems related to this stackoverflow question: http://stackoverflow.com/questions/10875179/fragile-and-verbose-code-using-xml-conduit

Two possibilities:
Implement this: Data.Conduit.List.map stripNamespace
Patch xml-conduit

@Twinside has a new svg-tree package for loading/serialising SVG files. It might be nice to use it here so this package would only need to do the Document -> Diagram conversion.