use element applies referenced viewBox scaling. FontManager created.

[peracto]

Before I begin, apologies, this is my first ever pull request ...

1. The 'use' element.

When referencing a element that contains a viewBox attribute - the result should be scaled using the width/height defined on the use element and the width/height of the viewbox.

I created a test case ... "__issue-323-02-01" - but realise that I've not followed any proper naming convention.

2. Fonts ... My use case required the use of adhoc fonts. The existing method SVGElement.PrivateFonts - partially solved the issue, but not completely ... Introducing the SvgFontManager.

When a font is requested in the render process, if the font is not found as an embedded SvgFont, it defers to the SvgFontManager.FindFont method. The SvgFontManager.FindFont searches a dictionary of fonts (pre loaded with the system fonts). If a font can't be found and a callback has been provided - then the callback should perform any validation and return a font (or null if not found/error). When the SvgFontManager can't identify the font, we then fallback to the SVGElement.PrivateFont method.

Example usage.

        SvgFontManager.FontLoaderCallback = name =>
        {
            var ff = Path.Combine(Config.FontsFolder, name + ".ttf");
            if (!File.Exists(ff))
            {
                Log.Error($"Font request ({name}) does not exist at {ff}");
                return null;
            }

            var rc = SvgFontManager.AddFontFile(ff);
            if (rc == null) Log.Error($"Font request ({name}) font not loaded. {ff}");
            return rc;
        };

[mrbean-bremen]

this is my first ever pull request

Congratulations, and thanks :)

I created a test case ... "__issue-323-02-01" - but realise that I've not followed any proper naming convention.

I think it would be better to rename it to __pull_request-414-01 to relate it to the correct PR, but other than that, it looks good to me! I will have a closer look tomorrow, but so far it looks sensible.

[mrbean-bremen]

Could you please add a description what this does and how it is used (along the lines you put in the comments in this PR already)?

[peracto]

complete.