Add utility function to GUICommon.hlsl for MSDF fonts sampling in shaders

#3944

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;
 };

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)

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