Draw a character with 2 color in Android

Question

I am trying to achieve a karaoke text animation in a Textview. Something like this:

In order for it to be smooth, I want to find a way to draw a 2-color character(like s in the image).

I found this link but the HalfColorSpan there didn't draw anything.

Is there any way to achieve it?

P/S: I have thought of LinearGradient, but this code only set the gradient VERTICALLY.

class HalfColorSpan extends CharacterStyle implements UpdateAppearance {
    private final static String TAG = "DrawableSpanTest.HalfColorSpan";
    @Override
    public void updateDrawState(TextPaint paint) {
        paint.setStyle(Paint.Style.FILL);
        Shader shader = new LinearGradient(0, 0, 0, 80, new int[]{PROCESSED_COLOR, UNPROCESSED_COLOR}, new float[]{0, 1},
                Shader.TileMode.CLAMP);
        paint.setShader(shader);
    }
}