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;
}