FloatingActionButton.java 文件源码

private Drawable createInnerStrokesDrawable(final int color, float strokeWidth) {
  if (!mStrokeVisible) {
    return new ColorDrawable(Color.TRANSPARENT);
  }

  ShapeDrawable shapeDrawable = new ShapeDrawable(new OvalShape());

  final int bottomStrokeColor = darkenColor(color);
  final int bottomStrokeColorHalfTransparent = halfTransparent(bottomStrokeColor);
  final int topStrokeColor = lightenColor(color);
  final int topStrokeColorHalfTransparent = halfTransparent(topStrokeColor);

  final Paint paint = shapeDrawable.getPaint();
  paint.setAntiAlias(true);
  paint.setStrokeWidth(strokeWidth);
  paint.setStyle(Style.STROKE);
  shapeDrawable.setShaderFactory(new ShaderFactory() {
    @Override
    public Shader resize(int width, int height) {
      return new LinearGradient(width / 2, 0, width / 2, height,
          new int[] { topStrokeColor, topStrokeColorHalfTransparent, color, bottomStrokeColorHalfTransparent, bottomStrokeColor },
          new float[] { 0f, 0.2f, 0.5f, 0.8f, 1f },
          TileMode.CLAMP
      );
    }
  });

  return shapeDrawable;
}