Add option for clear type text

[bforlgreen]

Clear type text is a process to make text appear crisper at the same resolution. Whilst basic antialiasing makes text look less pixelated, it can also then make text look more blurry. Clear type is an extension to antialiasing that uses colours to "trick" us into perceiving the text is crisper.

On the left, no AA, so looks pixelated.
In the middle, AA has been applied (but in certain situations, like with a grey colour, it can look blurry)
On the right, AA with clear type

To enable ClearType in Skia, you have to set LcdRenderText on the Paint class to true, which will then enables "SubpixelAntialias". I am not sure why they use the name "LcdRenderText" instead of 'SubpixelAntialias'.

Unfortunately, this is not the only change you have to make to enable ClearType. You also have to set the SkSurfacesProperties within the SKElement class. To achieve this, you kind of have to copy the the SKElement class from the SkiaSharp code base.

Results ( you will need to zoom in)

[bclehmann]

Wonder if we should make this an enum, since setting LcdRenderText to true has no effect unless paint.IsAntialias is also true.

I'm thinking something along the lines of

enum TextAntialiasType {
  None,
  Antialias,
  SubpixelAntialias,
}

Then we can set the booleans but allow a simpler API. But we'll need to keep AntiAliasText to keep backwards compatibility. I think we should use getters and setters to enforce the current behaviour (if AntiAliasText is set to true we get the current AA behaviour, if it's false we get no AA). Not sure if setting it to true while subpixel AA is on should have no effect or if it should be set to non-subpixel AA.

[bclehmann]

I believe this is something that has to be enabled on the control, and I don't like the idea of having AA flags being placed in two very different places. I think the solution is probably making some TextAntialiasType a global field which is read in both places (maybe on the Plot class?). And if necessary we can preserve some way for the user to mix unantialiased text with AA text. But I'm not convinced that the user would want something like that.

[bforlgreen]

Yes, the problem is that you have to be able to set SKSurfaceProperties when creating the SKSurface, which you can only do by implementing your own SKElement class (SKElement is implemented in SkiaSharp)

The only clean way I can see to do it would be to have a copy of the SkiaSharp SKElement class inside of the ScottPlot library itself. But appreciate you won't want to do that just for this use case.

[bclehmann]

We already use SKElement on (most of) the controls. For example, see https://github.com/ScottPlot/ScottPlot/blob/main/src/ScottPlot5/ScottPlot5%20Controls/ScottPlot.WPF/Themes/Generic.xaml

Worst case scenario, we can subclass SKElement to provide our own OnRender function (relevant code for WPF is here: https://github.com/mono/SkiaSharp/blob/main/source/SkiaSharp.Views/SkiaSharp.Views.WPF/SKElement.cs). But I'm admittedly not that pleased at the idea of duplicating most of the function just to allow a slightly different SKSurface.Create call. Granted it doesn't look like these views are changed much, but it doesn't fill me with joy. I do also see some private methods and fields which we'd need to copy-paste for this to work.

This could also be achieved by copying , but that's not ideal, one of the big benefits of ScottPlot 5 is we don't normally need to copy bitmaps between the plot and the controls.