[API Proposal]: Trim friendly Font ToLogFont/FromLogFont

[kant2002]

Background and motivation

Right now WinForm use System.Drawing.Common.Font.ToLogFont/FromLogFont with their own interop structures. That API produce trimming warning. This API would serve same purpose as existing API, but provide trim friendly alternative.

API Proposal

namespace System.Drawing;

public sealed partial class Font
{
    public void ToLogFont<T>(ref T logFont, Graphics graphics) where T: struct, unmanaged  { throw null; }
    public static Font FromLogFont<T>(in T logFont) where T: struct, unmanaged { throw null; }
    public static Font FromLogFont<T>(in T logFont, IntPtr hdc) where T: struct, unmanaged { throw null; }
    public void ToLogFont<T>(ref T logFont) where T: struct, unmanaged { throw null; }
}

API Usage

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public unsafe struct MyLOGFONT
{
    public int lfHeight;
    public int lfWidth;
    public int lfEscapement;
    public int lfOrientation;
    public int lfWeight;
    public byte lfItalic;
    public byte lfUnderline;
    public byte lfStrikeOut;
    public byte lfCharSet;
    public byte lfOutPrecision;
    public byte lfClipPrecision;
    public byte lfQuality;
    public byte lfPitchAndFamily;
    private fixed char _lfFaceName[LF_FACESIZE];
}

// And similar 
var f = new Font();
MyLOGFONT interopStruct = default;
f.ToLogFont(ref interopStruct);

Alternative Designs

Ask users of this API, reimplement it itself within their application and make that code trim-friendly.

Risks

No response

Accompanying implementation dotnet/runtime#70224

[ghost]

Tagging subscribers to this area: @dotnet/area-system-drawing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

Right now WinForm use System.Drawing.Common.Font.ToLogFont/FromLogFont with their own interop structures. That API produce trimming warning. This API would serve same purpose as existing API, but provide trim friendly alternative.

API Proposal

namespace System.Drawing;

public sealed partial class Font
{
    public void ToLogFont<T>(ref T logFont, Graphics graphics) where T: struct, unmanaged  { throw null; }
    public static Font FromLogFont<T>(in T logFont) where T: struct, unmanaged { throw null; }
    public static Font FromLogFont<T>(in T logFont, IntPtr hdc) where T: struct, unmanaged { throw null; }
    public void ToLogFont<T>(ref T logFont) where T: struct, unmanaged { throw null; }
}

API Usage

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public unsafe struct MyLOGFONT
{
    public int lfHeight;
    public int lfWidth;
    public int lfEscapement;
    public int lfOrientation;
    public int lfWeight;
    public byte lfItalic;
    public byte lfUnderline;
    public byte lfStrikeOut;
    public byte lfCharSet;
    public byte lfOutPrecision;
    public byte lfClipPrecision;
    public byte lfQuality;
    public byte lfPitchAndFamily;
    private fixed char _lfFaceName[LF_FACESIZE];
}

// And similar 
var f = new Font();
MyLOGFONT interopStruct = default;
f.ToLogFont(ref interopStruct);

Alternative Designs

Ask users of this API, reimplement it itself within their application and make that code trim-friendly.

Risks

No response

Author:	kant2002
Assignees:	-
Labels:	api-suggestion, area-System.Drawing
Milestone:	-

[ViktorHofer]

@JeremyKuhne @RussKie, given that there's already a PR up for the implementation, should this get reviewed in one of the api design review meetings? Would anyone of you want to be the champion for it?

[JeremyKuhne]

@ViktorHofer sure, mark it and I'll represent.

[RussKie]

I'll watch the recording

[ViktorHofer]

Great, thank you. Sent out a mail.

[terrajobst]

How urgent is this?

[ViktorHofer]

@kant2002 can you answer @terrajobst's question regarding the priority of getting this into main?

[kant2002]

Personally I would like to have this in .Net 7, that increases chances that I annotate core WinForms libraries for trimming.

[bartonjs]

Video

• We made Interop.LOGFONT public and removed the genericness of the functions

namespace System.Drawing
{
    public sealed partial class Font
    {
        public void ToLogFont(out Interop.LOGFONT logFont, Graphics graphics)  { throw null; }
        public static Font FromLogFont(in Interop.LOGFONT logFont) { throw null; }
        public static Font FromLogFont(in Interop.LOGFONT logFont, IntPtr hdc) { throw null; }
        public void ToLogFont(out Interop.LOGFONT logFont) { throw null; }
    }
}

namespace System.Drawing.Interop
{
    public unsafe struct LOGFONT
    {
        public int lfHeight;
        public int lfWidth;
        public int lfEscapement;
        public int lfOrientation;
        public int lfWeight;
        public byte lfItalic;
        public byte lfUnderline;
        public byte lfStrikeOut;
        public byte lfCharSet;
        public byte lfOutPrecision;
        public byte lfClipPrecision;
        public byte lfQuality;
        public byte lfPitchAndFamily;
        private fixed char _lfFaceName[LF_FACESIZE];

        [UnscopedRef]
        public Span<char> lfFaceName => MemoryMarshal.CreateSpan(ref _lfFaceName[0], LF_FACESIZE);
    }
}

[elachlan]

Now the API change is approved, can we reopen dotnet/runtime#70224?

[ViktorHofer]

@kant2002 feel free to re-open your PR and we can give it another glance.

[elachlan]

@kant2002 did you want to reroll your patch now System.Drawing has moved to winforms?

[JeremyKuhne]

I've implemented this and will be putting up a PR tomorrow.