feat: Dynamic Runtime Rasterized MSDF Sprite Font by yuechen-li-dev · Pull Request #3055 · stride3d/stride

yuechen-li-dev · 2026-02-04T10:20:03Z

PR Details

This PR adds an experimental runtime MSDF font path to Stride’s sprite font system.

Introduction

Stride’s current sprite font rasterization options each have trade-offs. Dynamically generating MSDF glyphs on-demand is the common approach in modern engines (e.g., Unity/Unreal): it combines the benefits of Stride’s runtime rasterized fonts (large character sets like CJK) with offline SDF/MSDF advantages (smooth edges at high resolution, easy scaling) with minimal downsides.

Implementation

Dynamic MSDF generation differs substantially from Stride’s existing static SDF pipeline.

Uses SharpFont (already a Stride dependency) to extract glyph outlines on-demand when glyphs are requested at runtime.
Generates MSDF textures asynchronously via a bounded Channel + worker pool, then uploads into the font atlas.
The MSDF rasterizer is intentionally modular / swappable to keep the pipeline future-proof.

Rasterizer backends

Two managed, cross-platform MSDFGen ports are included (no P/Invoke):

Remora.MSDFGen: lighter/older, fewer features
MSDFGen-Sharp / msdfgen.core: newer, more features, slightly better results on some fonts

Also included:

Two debug rasterizers:
- a simple pattern output backend
- an outline diagnostic backend

Notes / limitations

"Default Size" parameter is used for baking, keep it relatively large (64+) for best results.
Some fonts (especially those with overlapping / self-intersecting contours) can produce repeatable MSDF artifacts (notably in punctuation/CJK). Current workaround: preprocess fonts in FontForge (Remove Overlap / Simplify / Correct Direction). This keeps runtime lightweight and avoids bundling heavy geometry cleanup.
Game Studio “Play” vs running from Visual Studio can differ in dependency deployment. Ensure the MSDF backend assemblies are present in the runtime output; if needed, run the game via VS at least once so dependencies get copied/resolved. Otherwise, fonts may render in the editor but not in-game.
Thumbnail preview for runtime MSDF fonts is currently blank; I wasn’t able to find a clean fix yet.

Testing

Verified glyph generation + atlas upload in the editor.
Verified runtime behavior when launched from Visual Studio.
Used debug backends to validate atlas upload/sampling independently of MSDF generation.

Core files:

RuntimeSignedDistanceFieldSpriteFont.cs
SharpFontOutlineExtractor.cs
MsdfGenCoreRasterizer.cs (MSDFGen-Sharp backend)
RemoraMsdfRasterizer.cs
Pipeline glue (MsdfGenerationPipeline.cs, etc.)

Thanks. This took a lot longer than I thought it would.

Comparison

Existing Runtime Rasterized Font:

New Runtime MSDF Font:

Related Issue

#2584

Types of changes

Docs change / refactoring / dependency upgrade
Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)

Checklist

My change requires a change to the documentation.
I have added tests to cover my changes.
All new and existing tests passed.
I have built and run the editor to try this change out.

This reverts commit 0dc668c.

…-in-runtimesigneddistancefieldspritefon Remove runtime SDF bake size plumbing and use SpriteFont.Size for glyph generation.

…ary integration.

…stride into Runtime-SDF-Font

…ey cache into ConcurretDictionaries to future-proof multithreaded calls in the future.

yuechen-li-dev · 2026-02-04T10:22:22Z

@dotnet-policy-service agree

Eideren · 2026-02-04T18:49:54Z

We already have an offline SDF option - but I understand that the reason you implemented this feature is because non-latin character sets tend to be very large and require a high resolution. Offline SDF we currently have wouldn't work because it would have to cover multiple thousands of characters with a fairly high resolution, potentially blowing out build sizes.

Definitely cool to see, now, is there a particular reason why this PR specifically sidesteps using most of the logic already setup for offline SDF ?

Also, as it stands, the limitations seems a bit like a show stopper. Our engine already has enough quirk as it is, best to fix those before we merge this in

Eideren · 2026-04-05T17:47:59Z

Changing this to draft while you work on it, let me know when you're ready for another review :)

yuechen-li-dev · 2026-04-05T18:14:10Z

Changing this to draft while you work on it, let me know when you're ready for another review :)

Yeah, sorry, I don't think I will be able to work on this for quite some time as the direct results from my work on Stride had led to some major projects that are taking priority right now, so unfortunately, I would not be able to work on this for a while. Feel free to poke around the code and continue my work, the main concern from me that I'm honestly unsure what to do about is that the thumbnail generation is not async aware, and I don't want to rewrite the entire font pipeline to fit async in when it doesn't really need it since async kinda infects everything, and of course, harden the entire MSDF pipeline via unit tests, which should be fairly simple with LLMs.

Thanks for the support, I'll circle back to this when I have time.

Ethereal77 · 2026-04-10T09:15:52Z

sources/engine/Stride.Graphics/Font/FontManager.cs

+            using (var fontStream = contentManager.OpenAsStream(fontPath))
+            {


This change is not needed. Also, it adds a brace that is never closed?

Weird. I just merged master into this feature branch from VS and took incoming change to get this branch sync'd since I have a little bit of time to work on this. Give me a min, let me look it over.

Ethereal77 · 2026-04-10T09:21:38Z

sources/engine/Stride.Assets/SpriteFont/SpriteFontAssetCompiler.cs

            }
        }

+        internal class RuntimeSignedDistanceFieldFontCommand : AssetCommand<SpriteFontAsset>


Just a little thought: Is not this file a bit full of classes already? Would not make more sense to split the internal classes to their own files to ease discovery?

I don't think I've added much to this file other than what is needed to implement runtime MSDF, and I'd like to keep the scope of this PR narrow to just feature implementation cleanly right now. Refactoring/cleaning up existing file will probably have to be another pass.

Ethereal77 · 2026-04-10T10:41:08Z

sources/engine/Stride.Graphics/Font/FontManager.cs

+DequeueRequest:

-                    // update the generated cached data
+// update the generated cached data


Indentation

Ethereal77 · 2026-04-10T10:46:54Z

sources/engine/Stride.Graphics/Font/FontSystem.cs

        /// <param name="style">The font style.</param>
        /// <returns>A <see cref="SpriteFont"/> instance if the font is registered; otherwise, <c>null</c>.</returns>
-        public SpriteFont? LoadRuntimeFont(string fontName, float defaultSize = 16f, FontStyle style = FontStyle.Regular)
+        public SpriteFont LoadRuntimeFont(string fontName, float defaultSize = 16f, FontStyle style = FontStyle.Regular)


The XML docs still says otherwise, <c>null</c>. Why was the return type changed from SpriteFont? to non-null SpriteFont?

Good catch. I think I removed it too hastily without looking at it too carefully. File should be properly nullable now.

Ethereal77 · 2026-04-10T10:54:08Z

sources/engine/Stride.Graphics/Font/RuntimeSignedDistanceFieldSpriteFont.cs

+namespace Stride.Graphics.Font
+{    /// <summary>
+     /// A dynamic font that asynchronously generates multi-channel signed distance mapping for glyphs as needed, enabling sharp, smooth edges and resizability.
+     /// </summary>
+    [ReferenceSerializer, DataSerializerGlobal(typeof(ReferenceSerializer<RuntimeSignedDistanceFieldSpriteFont>), Profile = "Content")]
+    [ContentSerializer(typeof(RuntimeSignedDistanceFieldSpriteFontContentSerializer))]
+    [DataSerializer(typeof(RuntimeSignedDistanceFieldSpriteFontSerializer))]
+
+    internal sealed class RuntimeSignedDistanceFieldSpriteFont : SpriteFont


Blank line between attributes and class, Comments on the same line as the brace

Should be fixed after the partial class split.

Ethereal77 · 2026-04-10T10:55:44Z

sources/engine/Stride.Graphics/Font/RuntimeSignedDistanceFieldSpriteFont.cs

+        // Keep today’s encoding behavior explicit and centralized.
+        private static readonly DistanceEncodeParams DefaultEncode = new(Bias: 0.4f, Scale: 0.5f);
+
+        private DistanceFieldParams GetDfParams()


Try to not use abbreviations: GetDfParams() -> GetDistanceFieldParams() or something alike. Reads better in callstacks and is apparent what it does at a quick glance

Fixed after partial class split.

VaclavElias · 2026-04-10T11:07:16Z

Another alternative worth considering is SixLabors Fonts (from the creators of ImageSharp). Btw, it also does text layouting

@Ethereal77, not sure if the license is ok here https://github.com/SixLabors/Fonts/blob/main/LICENSE, and how it would affect commercial games.

Ethereal77 · 2026-04-10T11:17:48Z

sources/engine/Stride.Graphics/Font/RuntimeSignedDistanceFieldSpriteFont.cs

I think this file has too many responsibilities and is too long. For contrast, SignedDistanceFieldSpriteFont is just the serializable definition of a SDF sprite font. This file is not only that, but also has infrastructure for asynchronous atlas building, EDT transform computation, and maybe other things.

I would split those parts to the systems in charge of managing fonts, or to components specialized in each of those tasks that can as an added benefit be tested in isolation (and maybe even used in some other part where they may be beneficial)

To avoid a major architecture rewrite, I've split the file into 3 partial classes: the font file, the generator/rasterizer seams, and the fallback bitmap based SDF builder. If there is need, I think there could be a bigger split later on, but the seams are already pretty clean.

Ethereal77 · 2026-04-10T11:33:29Z

Another alternative worth considering is SixLabors Fonts (from the creators of ImageSharp). Btw, it also does text layouting

@Ethereal77, not sure if the license is ok here https://github.com/SixLabors/Fonts/blob/main/LICENSE, and how it would affect commercial games.

I think they changed the license some time ago to allow free use for open-source projects, and to be also free if the library is consumed transitively (i.e., through Stride). The paid license would only apply if your project is closed-source and you are using the library directly. Correct me if I'm wrong

VaclavElias · 2026-04-10T11:51:02Z

..and to be also free if the library is consumed transitively (i.e., through Stride). The paid license would only apply if your project is closed-source and you are using the library directly. Correct me if I'm wrong

I believe you are right.

…y forcing warm-up before async.

…agnostic-test Add bounded runtime SDF glyph upload convergence diagnostic

…now uses rasterized preview in asset thumbnails for editor stability/readability.

…classes from the RT-SDF font file.

…ests-for-runtimesigneddistancefieldspri Finalize Runtime SDF diagnostics into focused regression tests

yuechen-li-dev and others added 26 commits January 28, 2026 20:09

M1: Added Runtime SDF placeholder.

d49b9ff

M2. MSDF Cache Scaffold.

3275c16

M3: Font works end to end, renders ugly circles.

5d9185f

M4 WIP: Buggy implementation with flickers so far.

75f5369

It works, but each text spins computer like jet engine.

1fa1cd4

Async implementation and various optimizations.

2f0b165

Fixed bad copypaste for SpriteFontAssetCompiler.cs

dd4f8e0

Less sloppy Async.

0dc668c

Revert "Less sloppy Async."

69e2f15

This reverts commit 0dc668c.

Remove runtime SDF bake size plumbing

7ad4caa

Merge pull request #4 from yuechen-li-dev/codex/refactor-glyph-sizing…

b04c959

…-in-runtimesigneddistancefieldspritefon Remove runtime SDF bake size plumbing and use SpriteFont.Size for glyph generation.

Adjusted default bakesize to 64 so SDF is high quality.

d5d9576

Merge branch 'stride3d:master' into Runtime-SDF-Font

18e227d

Changed to channel based async design.

217a8fd

Channel based refactor for async, introduce interface for easier libr…

e2e9f09

…ary integration.

See above message. Wrong commit lol.

ae2e234

Merge branch 'Runtime-SDF-Font' of https://github.com/yuechen-li-dev/…

a0058c4

…stride into Runtime-SDF-Font

refactor for future MSDFGeneration.

914819d

Initial wiring. Need to fix generationPipeline.

048b521

Ok, it renders but only as blocks or dots. Debug time.

d7d8d5b

It works! Mostly. Need to squash some font specific bugs.

dbba408

Next try with MsdfGen too.

a22eb17

Comment edits.

e455a49

clean up gitignore of temp file.

cc65561

Move offset logic out of ApplyUploadedGlyph for safety. Change glyphk…

4d9159c

…ey cache into ConcurretDictionaries to future-proof multithreaded calls in the future.

Minor changes so VS would have less messages.

dd6b53a

Eideren added the area-UI label Feb 4, 2026

Eideren changed the title ~~Add Dynamic Runtime Rasterized MSDF Sprite Font~~ feat: Dynamic Runtime Rasterized MSDF Sprite Font Feb 4, 2026

remove unused bool isClosed definition from outline extractor.

0753019

Eideren marked this pull request as draft April 5, 2026 17:48

Merge master into runtime-msdf-font

0a089c8

Ethereal77 reviewed Apr 10, 2026

View reviewed changes

yuechen-li-dev and others added 15 commits April 10, 2026 05:19

Minor fix to align change with current master repo.

887ebba

Added unit test for RT-SDF font path. Made YamlSerializer stricter.

5148580

Step 1: Minimal initial fix for thumbnail generation of RT-SDF font b…

6de2b12

…y forcing warm-up before async.

Step 2: Diagnosed and fixed layout state mutation bug.

350f348

Step 3 of Diagnostic test.

9f062ef

Add bounded runtime SDF glyph upload convergence diagnostic

20d3d2e

Merge pull request #5 from yuechen-li-dev/codex/add-bounded-warmup-di…

9883203

…agnostic-test Add bounded runtime SDF glyph upload convergence diagnostic

Fix runtime SDF font thumbnail generation in the editor. Runtime SDF …

3218db5

…now uses rasterized preview in asset thumbnails for editor stability/readability.

Register Runtime SDF to be accessible in Game Studio.

e14b84b

FontManager indentation.

5694d01

Split generator functionality/bitmap based SDF fallback into partial …

7b986e1

…classes from the RT-SDF font file.

Flipped font in outline diagnostic rasterizer to correct orientation.

beb3a62

Added nullablility on FontSystem.cs.

f3d4c00

Finalize runtime SDF layout diagnostics as regression tests

dd6dcf4

Merge pull request #6 from yuechen-li-dev/codex/finalize-regression-t…

c02a360

…ests-for-runtimesigneddistancefieldspri Finalize Runtime SDF diagnostics into focused regression tests

		using (var fontStream = contentManager.OpenAsStream(fontPath))
		{

Uh oh!

Conversation

yuechen-li-dev commented Feb 4, 2026

PR Details

Introduction

Implementation

Rasterizer backends

Notes / limitations

Testing

Core files:

Comparison

Related Issue

Types of changes

Checklist

Uh oh!

yuechen-li-dev commented Feb 4, 2026

Uh oh!

Eideren commented Feb 4, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Eideren commented Apr 5, 2026

Uh oh!

yuechen-li-dev commented Apr 5, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

VaclavElias commented Apr 10, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Ethereal77 commented Apr 10, 2026

Uh oh!

VaclavElias commented Apr 10, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Eideren commented Feb 4, 2026 •

edited

Loading