computeMorphFrame function

Implementation

MorphFrame computeMorphFrame({
  required double value,
  required Rect sourceRect,
  required Rect targetRect,
  required ShapeBorder sourceShape,
  required ShapeBorder targetShape,
  required Color sourceColor,
  required Color targetColor,
  required double maxScrimOpacity,
  double sourceElevation = 0,
  double targetElevation = 24,
}) {
  final double p = clampDouble(value, 0, 1);

  final ({Rect rect, double? sourceRadius, double? targetRadius}) geometry =
      morphFlightGeometry(
        value: value,
        sourceRect: sourceRect,
        targetRect: targetRect,
        sourceShape: sourceShape,
        targetShape: targetShape,
      );
  final Rect rect = geometry.rect;

  final double targetReveal = _targetFade.transform(p);

  double? cornerRadius;
  ShapeBorder shape;
  if (geometry.sourceRadius == null || geometry.targetRadius == null) {
    shape = ShapeBorder.lerp(sourceShape, targetShape, p) ?? targetShape;
  } else {
    cornerRadius = morphConcentricRadius(
      geometry.sourceRadius!,
      geometry.targetRadius!,
      p,
      rect,
    );
    shape = _shapeFromRadius(sourceShape, targetShape, cornerRadius);
  }

  return MorphFrame(
    rect: rect,
    shape: shape,
    cornerRadius: cornerRadius,
    sourceOpacity: 1 - _sourceFade.transform(p),
    targetOpacity: targetReveal,
    targetScale: lerpDouble(0.95, 1, targetReveal)!,
    scrimOpacity: maxScrimOpacity * _scrimFade.transform(p),
    // The shadow belongs to the morphing container (the Material
    // container-transform guideline): the shuttle starts with exactly
    // the button's shadow and grows it continuously into the container
    // one - no shadow pop when the tag hides or at handoff. The lerp
    // rides p^1.5, not p: linear shadow reads as a hover near the
    // source end (a button-sized container carrying a quarter of the
    // dialog's elevation floats a layer above its resting self, and a
    // slow profile makes that a scene), while too-flat a curve starves
    // the middle of the "card" cue - a big surface with a button's
    // shadow reads as the button deformed, not a dialog materializing.
    // p^1.5 keeps the settle tail at the button's own shadow and gives
    // the mid-flight surface its card depth; symmetric, still a pure
    // function of the value.
    elevation: lerpDouble(sourceElevation, targetElevation, p * math.sqrt(p))!,
    surfaceColor: Color.lerp(
      sourceColor,
      targetColor,
      _surfaceBlend.transform(p),
    )!,
  );
}