Enable checking if PatternUnits or PatternContentUnits was actually set

[wieslawsoltes]

Reference Issue

The #668 actually broke Svg.Skia pattern rendering, did not see this as breaking at first. In order to correctly render pattern, pattern property inheritance must be used to check for inherited values. As #668 removed invalid inherited enum value it broke Svg.Skia as it does not have access to internal fields and those are necessary to provide information if actually PatternUnits or PatternContentUnits was set.

What does this implement/fix? Explain your changes.

Adds HasPatternUnits() and HasPatternContentUnits() methods to check if field has actually a value.

Any other comments?

[wieslawsoltes]

This is my code in Svg.Skia used for pattern rendering:

https://github.com/wieslawsoltes/Svg.Skia/blob/1298cbf0cd386f8694d97f7911432909fefbfa01/src/Svg.Skia/SvgPaintingExtensions.cs#L570-L595

[wieslawsoltes]

Hiding such internals neccessary for proper rendering will make #590 much harder to achieve.

[H1Gdev]

I think this PR solution is ad hocery.
Inherit was returned...

https://github.com/vvvv/SVG/blob/3efa867fb69ee2c68a59f5c1e8b92c988e94e1c7/Source/Painting/SvgPatternServer.cs#L155-L183

I think we should think of a way to return linked value in properties.

[wieslawsoltes]

I think we should think of a way to return linked value in properties.

Agree with that, returning correct linked value in properties is important and necessary in other place too.

[H1Gdev]

@wieslawsoltes
@mrbean-bremen

Temporary methods that have been added in this PR do not know when to be deleted.
So I think it should be stated in comments etc.

[wieslawsoltes]

@wieslawsoltes
@mrbean-bremen

Temporary methods that have been added in this PR do not know when to be deleted.
So I think it should be stated in comments etc.

I think we can revert this changes.

I am using different method and not relying on internals.

https://github.com/wieslawsoltes/Svg.Skia/blob/fa2cdcfbab6280e359657f9b8d930b4867ccae29/src/Svg.Skia/SvgPaintingExtensions.cs#L771
https://github.com/wieslawsoltes/Svg.Skia/blob/fa2cdcfbab6280e359657f9b8d930b4867ccae29/src/Svg.Skia/SvgExtensions.cs#L277-L284

This comes from from my work on using href properties for linear/radial gradients in Svg.Skia

https://github.com/wieslawsoltes/Svg.Skia/blob/fa2cdcfbab6280e359657f9b8d930b4867ccae29/src/Svg.Skia/SvgPaintingExtensions.cs#L316-L347
https://github.com/wieslawsoltes/Svg.Skia/blob/fa2cdcfbab6280e359657f9b8d930b4867ccae29/src/Svg.Skia/SvgPaintingExtensions.cs#L501-L540