TextView does not allow changing of read-only text background

[Error-String-Expected-Got-Nil]

Non-standard bug report format because I'm not entirely sure this is a bug, but would be surprised if it isn't. I've already found the offending code snippet, but want to check this is actually a bug before making a PR or anything.

In TextView:

Terminal.Gui/Terminal.Gui/Views/TextView.cs

Lines 3997 to 4009 in b46b778

	Attribute? cellAttribute = line [idxCol].Attribute is { } ? line [idxCol].Attribute : ColorScheme?.Disabled;
	Attribute attribute;
	if (cellAttribute!.Value.Foreground == cellAttribute.Value.Background)
	{
	attribute = new (cellAttribute.Value.Foreground, cellAttribute.Value.Background);
	}
	else
	{
	attribute = new (cellAttribute.Value.Foreground, ColorScheme!.Focus.Background);
	}
	SetAttribute (attribute);

This is in the OnDrawReadOnlyColor() method, which fires when drawing read-only text. This triggers the DrawReadOnlyColor event, which allows you to modify the attributes of drawn Cells to change the color.

The problem is that this leaves no way to manually set both the foreground and background colors at the same time: If they are different, the foreground will be kept, but the background will be set to correspond with the TextView's ColorScheme. If they are the same, you can change the background color, but then of course the text is illegible.

The other color selection methods simply check if the attribute was null, set it to a default if it was, and use it as-is otherwise. I'm not sure why that isn't the case here as well, and it doesn't feel like this is intentional, as it means the only way to change the read only text color is to derive the class and override the function, which isn't necessary for any other color choices.

[YourRobotOverlord]

Check this out, it might address what you're experiencing:
#457

Also, this is how I'm handling setting the read-only background:

        // this is to make text readable when readonly, which renders text as disabled
        readOnlyTextViewScheme = new ColorScheme(schemes["Base"])
        {
            Focus = new Attribute(new Color("#00FF6A"), new Color("#16161e")),
            Disabled =  new Attribute(new Color("#c0caf5"), new Color("#16161e")),
        };

// elsewhere:
textView.ColorScheme = readOnlyTextViewScheme

Example

[Error-String-Expected-Got-Nil]

Hmm, that does seem like a decent workaround. Appreciated.

[tig]

I hope to fix the underlying issues that make this challenging here:

• Fixes #4057 - MASSIVE! Fully implements ColorScheme->Scheme + VisualRole + Colors.->SchemeManager.  #4062

[tig]

BTW, these lines are both bugs:

Attribute? cellAttribute = line [idxCol].Attribute is { } ? line [idxCol].Attribute : ColorScheme?.Disabled; 

ColorScheme!.Focus.Background

Views should really never access ColorScheme directly. The should use, instead GetDisabledColor (or, what will be GetAttributeForRole (VisualRole.Disabled) in #4062.