Draw transparent text with iText 7

PdfGenerator.java

class TextBox {

    private UUID uuid;

    private float x;
    private float y;
    private float width;
    private float height;
    
    private double angle;
    
    private PdfFont font;
    private float fontSize;

    private float characterSpacing;
    private float lineHeight;

    private int r,g,b,a;
    }

class PdfGenerator {
    private static void applyText(PdfPage page, TextBox box, UserText userText) {
        AffineTransform at = AffineTransform.getTranslateInstance(box.getX(), box.getY());
        at.concatenate(AffineTransform.getTranslateInstance(0, box.getHeight()));
        at.concatenate(AffineTransform.getRotateInstance(box.getAngle()));

        float[] matrix = new float[6];
        at.getMatrix(matrix);

        PdfCanvas canvas = new PdfCanvas(page);

        canvas.beginText()
                .setFontAndSize(box.getFont(), box.getFontSize())
                .setCharacterSpacing(box.getCharacterSpacing())
                .setLineWidth(box.getLineHeight())
                .setLeading(box.getFontSize()*box.getLineHeight())
                .setTextMatrix(matrix[0], matrix[1], matrix[2], matrix[3], matrix[4], matrix[5]);

        // color
        canvas.setFillColorRgb(box.getR()/255f, box.getG()/255f, box.getB()/255f);

        PdfExtGState gs1 = new PdfExtGState();
        gs1.setFillOpacity(box.getA()/255f);
        canvas.setExtGState(gs1);

        for(String s: userText.getContent().split("[\\r\\n]+")) {
            if(box.getFont().getWidth(s, box.getFontSize()) + s.length() * box.getCharacterSpacing() <= box.getWidth()) {
                canvas.newlineShowText(s);
            } else {
                StringBuilder sb = new StringBuilder();
                float width = 0;

                for(char character: s.toCharArray()) {
                    float charWidth = box.getFont().getWidth(Character.toString(character), box.getFontSize());
                    if (width + charWidth + box.getCharacterSpacing() > box.getWidth()) { // overflow...
                        // add the current string and reset
                        canvas.newlineShowText(sb.toString());
                        sb = new StringBuilder();
                        width = 0;
                    }
                    if(sb.length() > 0) {
                        width += box.getCharacterSpacing();
                    }
                    width += charWidth;
                    sb.append(character);
                }

                if(width > 0) {
                    canvas.newlineShowText(sb.toString());
                }
            }
        }


        canvas.endText();
    }
}