Htykuut

I'm trying to use CanvasSvgDocument::LoadFromXml(resourcecreator, hstring) to create a CanvasSvgDocument. I'm storing the strings of various svgs so that I can quickly recreate them at CreateResources() without accessing files on disk. Though it builds fine, the call always fails with "the parameter is incorrect" and hresult_invalid_argument. Here's the code:

CanvasSvgDocument nextSvg = CanvasSvgDocument::LoadFromXml(resourceCreator, xmlString);

The resourcecreator seems correct; I can look at its properties. The xmlstring is an hstring created by loading filedata to a std::string and using to_hstring to convert it. It looks correct when examined in the debugger. I had thought the problem might be that the svgs are marked with encoding="UTF-8", and that would seem to conflict with the text being converted to wide chars. But changing the encoding reference to UTF-16, or UTF-16LE, or removing it, doesn't seem to make a difference. Creating a test string that is wide in the first place doesn't make a difference. Changing the resourceCreator to resourceCreator.Device() makes no difference, nor does using CanvasDevice::GetSharedDevice(). Is there an example of LoadFromXml as it would be correctly used in C++/winrt? There must be some basic error in this one line of code. Using VS 15.9.0 Preview 6, SDK 17763. Thanks.
[Update] A clue may lie in an answer to this question: does CanvasSvgDocument::LoadAsync() do any editing of svg data, but LoadFromXml() does not? I see that these svg files load and display if created with LoadAsync(), but LoadFromXml() crashes unless I make certain edits to the string argument. What I did was to begin with a string consisting of nothing but an empty svg and then incrementally add back elements from one of the svg files. After numerous tests I found a single reference that crashes LoadFromXml - though the same svg loads as written if via LoadAsync. It looks like this in my argument to std::wstring (added the before the " throughout).

<g id="surface1"><use xlink:href="#surface4"/></g>

remove from that the

<use xlink:href="#surface4"/>

and the svg loads without crashing, but still will not show up when drawn. The #surface4 refers to the id of a previous g element.

I don't know enough about svg to make sense of this, but if someone knows whether LoadAsync "cleans up" an svg but LoadFromXml does not, it would help in finding an answer. Perhaps it is just not possible to use LoadFromXml to load an svg using file data?