From 88587fb6a4f3ad036cf073cb73441840353a2449 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Thu, 12 Mar 2026 20:24:03 +0100
Subject: [PATCH] Add utility function to `GUICommon.hlsl` for MSDF fonts
 sampling in shaders

#3944
---
 Content/Shaders/GUI.flax           |  4 +--
 Source/Engine/Render2D/FontAsset.h |  6 ++---
 Source/Shaders/GUI.shader          | 20 +++-----------
 Source/Shaders/GUICommon.hlsl      | 43 ++++++++++++++++++++++++++++++
 4 files changed, 51 insertions(+), 22 deletions(-)

diff --git a/Content/Shaders/GUI.flax b/Content/Shaders/GUI.flax
index 484f09f46..3e0ccc18f 100644
--- a/Content/Shaders/GUI.flax
+++ b/Content/Shaders/GUI.flax
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:551f893b015cd364911270816607651917545c83d28259c918018ff3ffc15937
-size 5333
+oid sha256:b816ba638bc37b8a8288e4c397ff5b708153057650fa6b626a109ba42d189694
+size 4721
diff --git a/Source/Engine/Render2D/FontAsset.h b/Source/Engine/Render2D/FontAsset.h
index c9966c68b..56cc3d655 100644
--- a/Source/Engine/Render2D/FontAsset.h
+++ b/Source/Engine/Render2D/FontAsset.h
@@ -77,7 +77,7 @@ API_ENUM() enum class FontRasterMode : byte
     Bitmap,
 
     /// <summary>
-    /// Use the MSDF generator to render font atlases. Need to be rendered with a compatible material.
+    /// Use the Multi-channel Signed Distance Field (MSDF) generator to render font atlases. Need to be rendered with a compatible material.
     /// </summary>
     MSDF,
 };
@@ -92,7 +92,7 @@ API_STRUCT() struct FontOptions
     DECLARE_SCRIPTING_TYPE_MINIMAL(FontOptions);
 
     /// <summary>
-    /// The hinting.
+    /// The font hinting used when rendering characters.
     /// </summary>
     API_FIELD() FontHinting Hinting;
 
@@ -102,7 +102,7 @@ API_STRUCT() struct FontOptions
     API_FIELD() FontFlags Flags;
 
     /// <summary>
-    /// The rasterization mode.
+    /// The font rasterization mode.
     /// </summary>
     API_FIELD() FontRasterMode RasterMode;
 };
diff --git a/Source/Shaders/GUI.shader b/Source/Shaders/GUI.shader
index b09a3474d..a8f9452e9 100644
--- a/Source/Shaders/GUI.shader
+++ b/Source/Shaders/GUI.shader
@@ -92,7 +92,7 @@ float4 PS_Font(VS2PS input) : SV_Target0
 	PerformClipping(input);
 
 	float4 color = input.Color;
-	color.a *= Image.Sample(SamplerLinearClamp, input.TexCoord).r;
+    color.a *= SampleFont(Image, input.TexCoord);
 	return color;
 }
 
@@ -102,22 +102,8 @@ float4 PS_FontMSDF(VS2PS input) : SV_Target0
 	PerformClipping(input);
 
 	float4 color = input.Color;
-	float3 msd = Image.Sample(SamplerLinearClamp, input.TexCoord).rgb;
-    float sd = max(min(msd.r, msd.g), min(max(msd.r, msd.g), msd.b));
-
-    uint width, height;
-    Image.GetDimensions(width, height);
-    float pxRange = 4.0f; // Must match C++ code
-    float unitRange = float2(pxRange, pxRange) / float2(width, height);
-
-    float2 dx = ddx(input.TexCoord);
-    float2 dy = ddy(input.TexCoord);
-    float2 screenTexSize = rsqrt(dx * dx + dy * dy);
-    float screenPxRange = max(0.5f * dot(screenTexSize, unitRange), 1.0f);
-    float screenPxDist = screenPxRange * (sd - 0.5f);
-
-    float opacity = saturate(screenPxDist + 0.5f);
-	return float4(color.rgb, opacity);
+    color.a *= SampleFontMSDF(Image, input.TexCoord);
+	return color;
 }
 
 float4 GetSample(float weight, float offset, float2 uv)
diff --git a/Source/Shaders/GUICommon.hlsl b/Source/Shaders/GUICommon.hlsl
index 14c8b1327..67f9daac4 100644
--- a/Source/Shaders/GUICommon.hlsl
+++ b/Source/Shaders/GUICommon.hlsl
@@ -54,4 +54,47 @@ void PerformClipping(VS2PS input)
     PerformClipping(input.ClipOriginAndPos.xy, input.ClipOriginAndPos.zw, input.ClipExtents);
 }
 
+float SampleFont(Texture2D font, float2 uv)
+{
+    return font.Sample(SamplerLinearClamp, uv).r;
+}
+
+float GetFontMSDFMedian(Texture2D font, float2 uv)
+{
+    float4 msd = font.Sample(SamplerLinearClamp, uv);
+    return max(min(msd.r, msd.g), min(max(msd.r, msd.g), msd.b));
+}
+
+float GetFontMSDFPixelRange(Texture2D font, float2 uv)
+{
+    uint width, height;
+    font.GetDimensions(width, height);
+    float pxRange = 4.0f; // Must match C++ code
+    float unitRange = float2(pxRange, pxRange) / float2(width, height);
+
+    float2 dx = ddx(uv);
+    float2 dy = ddy(uv);
+    float2 screenTexSize = rsqrt(dx * dx + dy * dy);
+    return max(0.5f * dot(screenTexSize, unitRange), 1.0f);
+}
+
+float SampleFontMSDF(Texture2D font, float2 uv)
+{
+    float sd = GetFontMSDFMedian(font, uv);
+    float screenPxRange = GetFontMSDFPixelRange(font, uv);
+    float screenPxDist = screenPxRange * (sd - 0.5f);
+    return saturate(screenPxDist + 0.5f);
+}
+
+float SampleFontMSDFOutline(Texture2D font, float2 uv, float thickness)
+{
+    float4 msd = font.Sample(SamplerLinearClamp, uv);
+    float sd = max(min(msd.r, msd.g), min(max(msd.r, msd.g), msd.b));
+    float screenPxRange = GetFontMSDFPixelRange(font, uv);
+    float thick = clamp(thickness, 0.0, screenPxRange * 0.5 - 1.0) / screenPxRange;
+    float outline = saturate((min(sd, msd.a) - 0.5 + thick) * screenPxRange + 0.5);
+    outline *= 1 - saturate(screenPxRange * (sd - 0.5f) + 0.5f);
+    return outline;
+}
+
 #endif