Advanced Font Effects
Introduction
KernSmith can generate fonts with effects that the TextRuntime property surface does not expose — outline color, gradient fills, SDF, color fonts, custom glyph subsets, and a choice of rasterizer backend. Drop shadow is on the property path when HasDropshadow is set (see TextRuntime Fonts); the fields below cover the rest. They all live on KernSmith.FontGeneratorOptions, but BmfcSave (the descriptor that drives the property path) only carries a small slice of those fields.
This page catalogs the effects available today and shows the FontGeneratorOptions fields that drive each one.
Property path vs direct KernSmith: TextRuntime exposes baked drop shadow through HasDropshadow, DropshadowColor (+ channel mirrors), DropshadowOffsetX/Y, and DropshadowBlur when an InMemoryFontCreator is registered — see TextRuntime Fonts.
Everything else on this page still requires constructing a BitmapFont via KernSmith yourself and assigning it directly to TextRuntime.BitmapFont — outline color, gradient fills, SDF, color fonts, custom glyphs, backend selection, HardShadow, and custom Padding. BmfcSave does not carry those fields.
For the full construction walkthrough (helper method, channel layout caveat, and BmfcSave-vs-from-scratch flows), see Font Strategies — Direct BitmapFont Assignment. This page focuses on the per-effect options without repeating that setup.
Baseline Setup
Each sample on this page assumes a small CreateBitmapFont(BmFontResult, GraphicsDevice) helper that wraps a BmFontResult into a BitmapFont — one Texture2D per atlas page, then the BitmapFont(Texture2D[], string) constructor. The helper body lives in Font Strategies — From KernSmith with Custom Options; copy it from there.
The samples below show only the FontGeneratorOptions mutation and the generate-and-assign step. Adapt the starting options either by building from BmfcSave via GumFontGenerator.BuildOptions or by constructing FontGeneratorOptions directly — both flows are covered in the same section.
Outline Color
TextRuntime.OutlineThickness controls outline width but not outline color — outlines on the property-driven path are always black. To pick the color, set OutlineR/G/B alongside Outline:
// Initialize
var options = KernSmith.Gum.GumFontGenerator.BuildOptions(bmfcSave);
options.Outline = 2;
options.OutlineR = 255;
options.OutlineG = 64;
options.OutlineB = 64;
KernSmith.BmFontResult result =
KernSmith.BmFont.GenerateFromSystem(bmfcSave.FontName, options);
BitmapFont bitmapFont = CreateBitmapFont(result, GraphicsDevice);Outlined fonts use a different channel layout than unoutlined fonts. GumFontGenerator.BuildOptions selects the right layout automatically based on bmfcSave.OutlineThickness. If you start from a bmfcSave with OutlineThickness = 0 and then bump options.Outline to a non-zero value, also set the outlined-text channel layout explicitly:
Drop Shadow
Drop shadows are baked into the atlas itself — the glyph and its shadow render in a single draw call. The property path covers the common case; direct FontGeneratorOptions remains for extras KernSmith exposes but TextRuntime does not.
Property path (TextRuntime)
Set HasDropshadow and the dropshadow fields on a TextRuntime when KernSmith is wired up. Gum maps them through BmfcSave → GumFontGenerator at generation time. See TextRuntime Fonts — Baked drop shadow for defaults, cache behavior, and a short sample.
Direct FontGeneratorOptions
Use this path when you need KernSmith-only knobs (HardShadow, custom Padding, or shadow combined with effects not on BmfcSave) or when building a shared BitmapFont outside the property system.
Set ShadowOffsetX/Y to position the shadow, ShadowR/G/B for color, and optionally ShadowOpacity, ShadowBlur, and HardShadow:
Because the shadow is baked into the glyph's own atlas cell, you may need to increase Padding to give the shadow room — otherwise blurred shadows can clip at the cell edge.
When HasDropshadow is true on the property path, GumFontGenerator leaves ChannelConfig unset so KernSmith keeps full RGBA in the atlas. A custom Channels assignment on a shadowed font routes through KernSmith's channel compositor and can discard baked shadow color — the same reason outlined fonts use a different layout than plain text. On the direct path, mirror that rule: do not override Channels when baking shadow unless you know the compositor layout you need.
Gradient Fill
Gradient fills run vertically by default (top color to bottom color). Set both start and end colors and KernSmith fills each glyph with the gradient:
GradientAngle rotates the gradient direction; GradientMidpoint (0.0–1.0) biases where the two colors meet.
SDF Rendering
Signed distance field (SDF) fonts encode glyph shapes as distance fields rather than rasterized pixels. SDF atlases scale up smoothly and can support runtime effects like dynamic outlines — but only if the renderer is set up to consume SDF data. Set options.Sdf = true to generate one:
Gum's default text renderer samples the atlas as a normal alpha-blended texture. An SDF atlas rendered this way will look soft or washed out rather than crisp. Consuming SDF properly requires a custom shader that does the distance-field cutoff. Generate-and-assign works today; the visual quality benefits depend on rendering setup that may not exist in your project. If you're not already using SDF shaders elsewhere, prefer a higher-resolution non-SDF atlas instead.
Custom Character Sets
BmfcSave.Ranges controls the character set on the property-driven path, but its format is the BMFont range string. For richer subsetting — for example a UI that only needs digits and a few specific glyphs, or a CJK build with hand-curated codepoints — use CharacterSet directly:
A tightly-subsetted atlas can be dramatically smaller than the default ASCII set — useful for a HUD font that only ever shows numbers, or a CJK font where you've pre-scanned your localization tables.
Custom Glyphs
CustomGlyphs lets you inject raw pixel data for specific codepoints — handy for inserting button-prompt icons (gamepad face buttons, key glyphs) into a normal text run so they flow inline with the surrounding text:
See the KernSmith.CustomGlyph type for the exact constructor surface — it expects raw pixel bytes, not an encoded PNG.
Color Fonts (Emoji)
For fonts with COLR/CPAL tables (color emoji fonts, color icon fonts), set ColorFont = true. ColorPaletteIndex selects a palette when the font ships multiple:
Backend Selection (FreeType vs StbTrueType)
KernSmith uses FreeType by default for glyph rasterization. FreeType produces the best results but requires a native library to be present. On platforms where that's a problem — most notably Blazor WASM — switch to the managed StbTrueType backend:
GumFontGenerator.Generate also takes a RasterizerBackend? argument as a shortcut for the same effect when you're not customizing other options.
Variation Axes
Variable fonts expose continuous axes (weight, width, slant, optical size, etc.) keyed by four-character tags. Pin axes to specific values via VariationAxes:
Super-Sampling
SuperSampleLevel renders glyphs at N times the requested size then downscales for smoother edges. Useful for large display text where the default rasterization looks a bit chunky:
Higher super-sampling levels cost proportionally more memory during generation.
Hinting
By default KernSmith enables FreeType's hinting, which improves crispness at small sizes. For large display sizes or stylized fonts you may prefer the smoother unhinted curves:
Related Pages
Font Strategies — Direct BitmapFont Assignment — full construction walkthrough.
BitmapFont — the runtime type these samples produce.
TextRuntime Fonts — the property surface; baked drop shadow and the fields that bypass direct assignment.
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