Programmatically creating icon to use as ItemizedOverlay drawable - Android

I am trying to programmatically draw a parking icon to place as the drawable for an itemized overlay on a map.

The icon consists of a blue square with a white 'P' in its centre of which I would like to programmatically change the colour of the square to denote different parking types.

I've tried creating it via the canvas using drawRect & drawText but I cannot find a simple way of centering the text in the square and I cannot find a way to center the canvas on the coordinates - it keeps wanting to anchor from the top left hand corner.

I've alternatively tried creating an XML layout to convert to a drawable but cannot achieve this either.

Is there an elegant solution for what I am trying to achieve?

public class TextDrawable extends Drawable {

    private final static int    TEXT_PADDING           = 3;
    private final static int    ROUNDED_RECT_RADIUS    = 5;

    private final String    text;
    private final Paint     textPaint;
    private final Rect      textBounds;
    private final Paint     bgPaint;
    private final RectF     bgBounds;

    public TextDrawable(String text, String backgroundColor, int textHeight) {

        this.text = text;

        // Text
        this.textPaint = new Paint();
        this.textBounds = new Rect();
        textPaint.setColor(Color.WHITE);
        textPaint.setARGB(255, 255, 255, 255);
        textPaint.setAntiAlias(true);
        textPaint.setSubpixelText(true);
        textPaint.setTextAlign(Paint.Align.CENTER); // Important to centre horizontally in the background RectF
        textPaint.setTextSize(textHeight);
        textPaint.setTypeface(Typeface.DEFAULT_BOLD);
        // Map textPaint to a Rect in order to get its true height
        // ... a bit long-winded I know but unfortunately getTextSize does not seem to give a true height!
        textPaint.getTextBounds(text, 0, text.length(), textBounds);

        // Background
        this.bgPaint = new Paint();
        bgPaint.setAntiAlias(true);
        bgPaint.setColor(Color.parseColor(backgroundColor));
        float rectHeight  = TEXT_PADDING * 2 + textHeight;
        float rectWidth   = TEXT_PADDING * 2 + textPaint.measureText(text);
        //float rectWidth   = TEXT_PADDING * 2 + textHeight;  // Square (alternative)
        // Create the background - use negative start x/y coordinates to centre align the icon
        this.bgBounds = new RectF(rectWidth / -2, rectHeight / -2, rectWidth / 2, rectHeight / 2);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawRoundRect(bgBounds, ROUNDED_RECT_RADIUS, ROUNDED_RECT_RADIUS, bgPaint);
        // Position the text in the horizontal/vertical centre of the background RectF
        canvas.drawText(text, 0, (textBounds.bottom - textBounds.top)/2, textPaint);
    }

    @Override
    public void setAlpha(int alpha) {
        bgPaint.setAlpha(alpha);
        textPaint.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(ColorFilter cf) {
        bgPaint.setColorFilter(cf);
        textPaint.setColorFilter(cf);
    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }
}