add shadow to a custom progress bar

[saeid0034]

Hi I have this class that im using to create a custom circular progress bar
header

#pragma once

#include "stdafx.h"

class CircularProgress : public QProgressBar
{
	Q_OBJECT

public:
	explicit CircularProgress(QWidget *parent = 0);
    void add_shadow();
    void set_value(int value);
    int value;
    int width;
    int height;
    int progress_width;
    int font_size;
    QColor progress_color;
    QColor text_color;
    QColor bg_color;

protected:
    void paintEvent(QPaintEvent*);

private:
    bool progress_rounded_cap;
    int max_value;
    // Text
    bool enable_text;
    QString font_family;
    QString suffix;
    // BG
    bool enable_bg;
    
};

cpp file

#include "circular_progress.h"

CircularProgress::CircularProgress(QWidget *parent)
	: QProgressBar(parent),
	value(0),
	width(200),
	height(200),
	progress_width(10),
	progress_rounded_cap(true),
	max_value(100),
	progress_color(0xff79c6),
	enable_text(true),
	font_family("Segoe UI"),
	font_size(12),
	suffix("%"),
	text_color(0xff79c6),
	enable_bg(true),
	bg_color(0x44475a)
{

}

void CircularProgress::add_shadow()
{
	QGraphicsDropShadowEffect* shadow = new QGraphicsDropShadowEffect(this);
	shadow->setBlurRadius(15);
	shadow->setXOffset(0);
	shadow->setYOffset(0);
	shadow->setColor(QColor(0, 0, 0, 80));
	this->setGraphicsEffect(shadow);
}

void CircularProgress::set_value(int value)
{
	this->value = value;
	this->repaint(); // Render progress bar after change value
}

void CircularProgress::paintEvent(QPaintEvent*)
{
	// SET PROGRESS PARAMETERS
	int width = this->width - this->progress_width;
	int height = this->height - this->progress_width;
	int margin = this->progress_width / 2;
	int value = this->value * 360 / this->max_value;

	// PAINTER
	QPainter paint = QPainter();
	paint.begin(this);
	paint.setRenderHint(QPainter::Antialiasing); // remove pixelated edges
	paint.setFont(QFont(this->font_family, this->font_size));

	// CREATE RECTANGLE
	QRect rect = QRect(0, 0, this->width, this->height);
	paint.setPen(Qt::NoPen);
	paint.drawRect(rect);

	// PEN
	QPen pen = QPen();
	pen.setWidth(this->progress_width);
	// Set Round Cap
	if (this->progress_rounded_cap)
		pen.setCapStyle(Qt::RoundCap);

	// ENABLE BG
	if (this->enable_bg)
		pen.setColor(QColor(this->bg_color));
	paint.setPen(pen);
	paint.drawArc(margin, margin, width, height, 0, 360 * 16);

	// CREATE ARC / CIRCULAR PROGRESS
	pen.setColor(QColor(this->progress_color));
	paint.setPen(pen);
	paint.drawArc(margin, margin, width, height, -90 * 16, -value * 16);

	// CREATE TEXT
	if (this->enable_text)
		pen.setColor(QColor(this->text_color));
	paint.setPen(pen);
	paint.drawText(rect, Qt::AlignCenter, QString("%1%2").arg(this->value).arg(this->suffix));

	// END
	paint.end();
}

everything working as I excepted, but just one thing missing, I want to add a drop shadow to progress bar (not the whole progress bar, just to the bar itself, but sadly I dont have any Idea, anyone can help? thanks.