lerp method Null safety
Interpolate between two text styles.
This will not work well if the styles don't set the same fields.
The t argument represents position on the timeline, with 0.0 meaning
that the interpolation has not started, returning a (or something
equivalent to a), 1.0 meaning that the interpolation has finished,
returning b (or something equivalent to b), and values in between
meaning that the interpolation is at the relevant point on the timeline
between a and b. The interpolation can be extrapolated beyond 0.0 and
1.0, so negative values and values greater than 1.0 are valid (and can
easily be generated by curves such as Curves.elasticInOut).
Values for t are usually obtained from an Animation<double>, such as
an AnimationController.
If foreground is specified on either of a or b, both will be treated
as if they have a foreground paint (creating a new Paint if necessary
based on the color property).
If background is specified on either of a or b, both will be treated
as if they have a background paint (creating a new Paint if necessary
based on the backgroundColor property).
Implementation
static TextStyle? lerp(TextStyle? a, TextStyle? b, double t) {
assert(t != null);
assert(a == null || b == null || a.inherit == b.inherit);
if (a == null && b == null) {
return null;
}
String? lerpDebugLabel;
assert(() {
lerpDebugLabel = 'lerp(${a?.debugLabel ?? _kDefaultDebugLabel} ⎯${t.toStringAsFixed(1)}→ ${b?.debugLabel ?? _kDefaultDebugLabel})';
return true;
}());
if (a == null) {
return TextStyle(
inherit: b!.inherit,
color: Color.lerp(null, b.color, t),
backgroundColor: Color.lerp(null, b.backgroundColor, t),
fontSize: t < 0.5 ? null : b.fontSize,
fontWeight: FontWeight.lerp(null, b.fontWeight, t),
fontStyle: t < 0.5 ? null : b.fontStyle,
letterSpacing: t < 0.5 ? null : b.letterSpacing,
wordSpacing: t < 0.5 ? null : b.wordSpacing,
textBaseline: t < 0.5 ? null : b.textBaseline,
height: t < 0.5 ? null : b.height,
leadingDistribution: t < 0.5 ? null : b.leadingDistribution,
locale: t < 0.5 ? null : b.locale,
foreground: t < 0.5 ? null : b.foreground,
background: t < 0.5 ? null : b.background,
shadows: t < 0.5 ? null : b.shadows,
fontFeatures: t < 0.5 ? null : b.fontFeatures,
fontVariations: t < 0.5 ? null : b.fontVariations,
decoration: t < 0.5 ? null : b.decoration,
decorationColor: Color.lerp(null, b.decorationColor, t),
decorationStyle: t < 0.5 ? null : b.decorationStyle,
decorationThickness: t < 0.5 ? null : b.decorationThickness,
debugLabel: lerpDebugLabel,
fontFamily: t < 0.5 ? null : b._fontFamily,
fontFamilyFallback: t < 0.5 ? null : b.fontFamilyFallback,
package: t < 0.5 ? null : b._package,
overflow: t < 0.5 ? null : b.overflow,
);
}
if (b == null) {
return TextStyle(
inherit: a.inherit,
color: Color.lerp(a.color, null, t),
backgroundColor: Color.lerp(null, a.backgroundColor, t),
fontSize: t < 0.5 ? a.fontSize : null,
fontWeight: FontWeight.lerp(a.fontWeight, null, t),
fontStyle: t < 0.5 ? a.fontStyle : null,
letterSpacing: t < 0.5 ? a.letterSpacing : null,
wordSpacing: t < 0.5 ? a.wordSpacing : null,
textBaseline: t < 0.5 ? a.textBaseline : null,
height: t < 0.5 ? a.height : null,
leadingDistribution: t < 0.5 ? a.leadingDistribution : null,
locale: t < 0.5 ? a.locale : null,
foreground: t < 0.5 ? a.foreground : null,
background: t < 0.5 ? a.background : null,
shadows: t < 0.5 ? a.shadows : null,
fontFeatures: t < 0.5 ? a.fontFeatures : null,
fontVariations: t < 0.5 ? a.fontVariations : null,
decoration: t < 0.5 ? a.decoration : null,
decorationColor: Color.lerp(a.decorationColor, null, t),
decorationStyle: t < 0.5 ? a.decorationStyle : null,
decorationThickness: t < 0.5 ? a.decorationThickness : null,
debugLabel: lerpDebugLabel,
fontFamily: t < 0.5 ? a._fontFamily : null,
fontFamilyFallback: t < 0.5 ? a.fontFamilyFallback : null,
package: t < 0.5 ? a._package : null,
overflow: t < 0.5 ? a.overflow : null,
);
}
return TextStyle(
inherit: b.inherit,
color: a.foreground == null && b.foreground == null ? Color.lerp(a.color, b.color, t) : null,
backgroundColor: a.background == null && b.background == null ? Color.lerp(a.backgroundColor, b.backgroundColor, t) : null,
fontSize: ui.lerpDouble(a.fontSize ?? b.fontSize, b.fontSize ?? a.fontSize, t),
fontWeight: FontWeight.lerp(a.fontWeight, b.fontWeight, t),
fontStyle: t < 0.5 ? a.fontStyle : b.fontStyle,
letterSpacing: ui.lerpDouble(a.letterSpacing ?? b.letterSpacing, b.letterSpacing ?? a.letterSpacing, t),
wordSpacing: ui.lerpDouble(a.wordSpacing ?? b.wordSpacing, b.wordSpacing ?? a.wordSpacing, t),
textBaseline: t < 0.5 ? a.textBaseline : b.textBaseline,
height: ui.lerpDouble(a.height ?? b.height, b.height ?? a.height, t),
leadingDistribution: t < 0.5 ? a.leadingDistribution : b.leadingDistribution,
locale: t < 0.5 ? a.locale : b.locale,
foreground: (a.foreground != null || b.foreground != null)
? t < 0.5
? a.foreground ?? (Paint()..color = a.color!)
: b.foreground ?? (Paint()..color = b.color!)
: null,
background: (a.background != null || b.background != null)
? t < 0.5
? a.background ?? (Paint()..color = a.backgroundColor!)
: b.background ?? (Paint()..color = b.backgroundColor!)
: null,
shadows: t < 0.5 ? a.shadows : b.shadows,
fontFeatures: t < 0.5 ? a.fontFeatures : b.fontFeatures,
fontVariations: t < 0.5 ? a.fontVariations : b.fontVariations,
decoration: t < 0.5 ? a.decoration : b.decoration,
decorationColor: Color.lerp(a.decorationColor, b.decorationColor, t),
decorationStyle: t < 0.5 ? a.decorationStyle : b.decorationStyle,
decorationThickness: ui.lerpDouble(a.decorationThickness ?? b.decorationThickness, b.decorationThickness ?? a.decorationThickness, t),
debugLabel: lerpDebugLabel,
fontFamily: t < 0.5 ? a._fontFamily : b._fontFamily,
fontFamilyFallback: t < 0.5 ? a.fontFamilyFallback : b.fontFamilyFallback,
package: t < 0.5 ? a._package : b._package,
overflow: t < 0.5 ? a.overflow : b.overflow,
);
}