BoxShadow.ToString() do not allow to parse it again (exception thrown)

[dbriard]

Describe the bug

The ToString() method of BoxShadow to not allow to Parse it again. It throw an exception.

To Reproduce

1. Create a BoxShadow with OffsetX=1, OffsetY=0, Blur=0, Color=#ffaa00
2. ToString => 1 #ffaa00
3. Try to parse it => if (p.Length < 3 || p.Length > 6) throw new FormatException();

Expected behavior

ToString() should write all BoxShadow properties all the time, or we cannot parse it again, and also we don't know what value in the string correspond to what properties...

I would like to do:
var boxShadow2 = BoxShadow.Parse(boxShadow1.ToString())

Environment

• Avalonia-Version: 11.0.6

Additional context

In the code below, we don't know don't know what value in the string correspond to what property...

internal void ToString(StringBuilder sb)
{
    if (this == default(BoxShadow))
    {
        sb.Append("none");
        return;
    }

    if (IsInset)
    {
        sb.Append("inset ");
    }

    if (OffsetX != 0.0)
    {
        sb.AppendFormat("{0} ", OffsetX.ToString(CultureInfo.InvariantCulture));
    }

    if (OffsetY != 0.0)
    {
        sb.AppendFormat("{0} ", OffsetY.ToString(CultureInfo.InvariantCulture));
    }

    if (Blur != 0.0)
    {
        sb.AppendFormat("{0} ", Blur.ToString(CultureInfo.InvariantCulture));
    }

    if (Spread != 0.0)
    {
        sb.AppendFormat("{0} ", Spread.ToString(CultureInfo.InvariantCulture));
    }

    sb.AppendFormat("{0}", Color.ToString());
}

[Gillibald]

OffsetX and OffsetY are required all the time

[dbriard]

@Gillibald Sure, but in the ToString method, if OffsetX or OffsetY is zero, it is skiped.

The two BoxShadow below produce the same output string, and cannot be parsed as they do not have a minimum of 3 values.
OffsetX=0 OffsetY=1 Color=Red => "1 Red"
OffsetX=1 OffsetY=0 Color=Red => "1 Red"

It is even worse when using other parameters, as we can't know if the 1 is for OffsetX or Y, Blur or Spread:
OffsetX=1 OffsetY=0 Color=Red => "1 Red"
OffsetX=0 OffsetY=0 Blur=1 Color=Red => "1 Red"

My suggestion is to remove the four zero checks in the ToString() and to always write OffsetX, Y, Blur, Spread in the output string.

[Gillibald]

It should look like so:

internal void ToString(StringBuilder sb)
{
    if (this == default(BoxShadow))
    {
        sb.Append("none");
        return;
    }

    if (IsInset)
    {
        sb.Append("inset ");
    }

    sb.AppendFormat("{0} ", OffsetX.ToString(CultureInfo.InvariantCulture)); 

    sb.AppendFormat("{0} ", OffsetY.ToString(CultureInfo.InvariantCulture));
    
    if (Blur != 0.0)
    {
        sb.AppendFormat("{0} ", Blur.ToString(CultureInfo.InvariantCulture));
    }

    if (Spread != 0.0)
    {
        sb.AppendFormat("{0} ", Spread.ToString(CultureInfo.InvariantCulture));
    }

    sb.AppendFormat("{0}", Color.ToString());
}

The other parameters are optional

[dbriard]

Personnally I never use Spread so that's fine to me, but if you keep the checks you cannot differentiate those cases:

Blur = 0 and Spread = 1
and Blur = 1 and Spread = 0

So I think it is better to always write all four values.