Icon Font isn't rendered into atlas correctly

[copygirl]

When I add OpenFontIcons to ImGui from memory, it seems to render the icons incorrectly into the texture atlas. They appear to be "filled out", like some of the vertices / paths that make up the font are incorrectly grouped together. Any idea what could cause this?

For context, I'm using a modified version of Thraka's fork of ImGui.NET (to be able to access internal functions) along with Silk.NET.OpenGL.Extensions.ImGui, which provides the OpenGL backend. I appear to be on ImGui 1.88, but I believe Silk.NET's version is built against 1.87.

My code is in C#. I don't think it'll help the C++ people, but I'll provide it for completion's sake:

var fontSize = 16;
void MergeIcons() => AddFontFromResources(io, "OpenFontIcons", fontSize,
	offset: 3, ranges: new[]{ (OpenFontIcons.MIN, OpenFontIcons.MAX) }, merge: true);
AddFontFromResources(io, "OpenSans"       , fontSize, offset: -1); MergeIcons();
AddFontFromResources(io, "OpenSans.Bold"  , fontSize, offset: -1); MergeIcons();
AddFontFromResources(io, "OpenSans.Italic", fontSize, offset: -1); MergeIcons();

private unsafe static ImFontPtr AddFontFromResources(
	ImGuiIOPtr io, string name, int size,
	Action<ImFontConfigPtr>? cfgAction = null,
	float offset = 0, (char, char)[]? ranges = null, bool merge = false)
{
	// TODO: FontConfig can be freed at the end of this method.
	//       Unfortunately, data has to stick around until font atlas is built.
	var cfg = new ImFontConfigPtr(ImGuiNative.ImFontConfig_ImFontConfig()) {
		GlyphOffset = new(0, offset),
		MergeMode   = merge,
	};
	// Set cfg.Name so the font has a nice display name in ImGui.
	var fullName = $"{name.Replace('.', ' ')} {size}pt";
	Encoding.UTF8.GetBytes(fullName, new Span<byte>(cfg.Name.Data, cfg.Name.Count));
	// If glyph ranges are specified, allocate unmanaged heap memory for them.
	if (ranges != null) {
		var rangesSpan = GlobalHeapAllocator.Instance.Allocate<char>(ranges.Length * 2 + 1);
		for (var i = 0; i < ranges.Length; i++)
			(rangesSpan[i * 2], rangesSpan[i * 2 + 1]) = ranges[i];
		rangesSpan[^1] = default;
		fixed (void* rangesPtr = rangesSpan)
			cfg.GlyphRanges = (IntPtr)rangesPtr;
	}
	// Use cfgAction to allow changing other font configs.
	cfgAction?.Invoke(cfg);

	// Grab the stream for this font from the assembly's resources.
	var file = $"gaemstone.Client.Resources.{name}.ttf";
	using var stream = typeof(Resources).Assembly.GetManifestResourceStream(file)
		?? throw new InvalidOperationException($"Resource '{file}' was not found");

	using var memoryStream = new MemoryStream();
	stream.CopyTo(memoryStream); // Write font file from resources to memory stream.
	memoryStream.WriteByte(0);   // Add a NUL termination character.
	var bytes = memoryStream.ToArray();

	// Copy the data into unmanaged memory and pass it to ImGui.
	var data = GlobalHeapAllocator.Instance.AllocateCopy<byte>(bytes);
	fixed (byte* dataPtr = data)
		return io.Fonts.AddFontFromMemoryTTF((IntPtr)dataPtr, size, size, cfg);
}

[copygirl]

Just found the time to try out a different font. This issue is not present with ForkAwesome.