Brush.java

Brush.java

private static class Brush implements ValueAnimator.AnimatorUpdateListener {

	private Bitmap brush;
	private Bitmap buffer;
	private int duration;
	private TextSurface textSurface;
	private Bitmap brushSample;
	private Canvas canvasBuffer;
	private Text text;
	private final float x;
	private final float y;
	private float width;
	private float height;
	private Canvas brushCanvas;
	private Rect src = new Rect();
	private Rect dst = new Rect();
	private final int sampleWidth;
	private int startOffset;
	private int endOffset;
	private float px;

	public Brush(
			Text text,
			float x,
			float y,
			float width,
			float height,
			int duration,
			TextSurface textSurface,
			Bitmap brushSample
	) {
		this.text = text;
		this.x = x;
		this.y = y;
		this.width = width;
		this.height = height;
		this.duration = duration;
		this.textSurface = textSurface;
		this.brushSample = brushSample;

		brush = Bitmap.createBitmap((int) width, (int) height, Bitmap.Config.ARGB_8888);
		buffer = Bitmap.createBitmap((int) width, (int) height, Bitmap.Config.ARGB_8888);
		brushCanvas = new Canvas(brush);
		canvasBuffer = new Canvas(buffer);
		sampleWidth = brushSample.getWidth();

		startOffset = 0;
		endOffset = -sampleWidth + startOffset;
	}

	public void onDraw(Canvas canvas, Paint paint) {
		moveBrush(paint);
		buffer.eraseColor(Color.TRANSPARENT);
		canvasBuffer.drawBitmap(brush, 0, 0, paint);
		canvas.drawBitmap(buffer, x, y - height, paint);
		canvas.drawText(text.getValue(), x, y, paint);
	}

	private void moveBrush(Paint paint) {
		float x = (width + endOffset) * px;
		src.set(0, 0, (int) (brushSample.getWidth() * px), brushSample.getHeight());
		dst.set(0, 0, brushSample.getWidth(), brushSample.getHeight());
		dst.offset((int) (x - startOffset), 0);
		brushCanvas.drawBitmap(brushSample, src, dst, paint);
	}

	Animator getAnimator() {
		ValueAnimator animator = ValueAnimator.ofFloat(0, 1);
		animator.setInterpolator(new FastOutSlowInInterpolator());
		animator.addUpdateListener(this);
		animator.setDuration(duration);
		return animator;
	}

	@Override public void onAnimationUpdate(ValueAnimator animation) {
		px = (float) animation.getAnimatedValue();
		textSurface.invalidate();
	}
}