QPushButton shadow

ButtonShadowBehavior.cpp

#include "ButtonShadowBehavior.hpp"

#include <QAbstractButton>
#include <QtWidgets/QGraphicsDropShadowEffect>
#include <QState>
#include <QStateMachine>
#include <QSignalTransition>
#include <QParallelAnimationGroup>
#include <QVariantAnimation>

namespace abvent::noon {
ButtonShadowBehavior::ButtonShadowBehavior(QAbstractButton* parent)
	: QObject(parent)
	, _button(parent) {
	install();
}

ButtonShadowBehavior::~ButtonShadowBehavior() {
	uninstall();
}

void ButtonShadowBehavior::install() {
	if (_installed)
		return;

	_installed = true;

	// Setup shadow.
	_shadow = new QGraphicsDropShadowEffect(_button);
	_shadow->setBlurRadius(_blurNormal);
	_shadow->setOffset(_offset);
	_shadow->setColor(_colorNormal);
	_button->setGraphicsEffect(_shadow);

	// Setup state machine.
	_stateMachine = new QStateMachine(this);
	auto stateNormal = new QState();
	auto statePressed = new QState();

	// Normal->Pressed
	auto normalToPressedTransition = stateNormal->addTransition(_button, &QAbstractButton::pressed, statePressed);
	{
		auto normalToPressedAnimation = new QParallelAnimationGroup(_stateMachine);

		auto blurAnimation = new QVariantAnimation(normalToPressedAnimation);
		blurAnimation->setDuration(_animationDuration);
		blurAnimation->setEndValue(_blurPressed);
		QObject::connect(blurAnimation, &QVariantAnimation::valueChanged, this, [this](const QVariant& value) {
			if (_shadow) {
				const auto newValue = value.toInt();
				_shadow->setBlurRadius(newValue);
			}
		});

		auto colorAnimation = new QVariantAnimation(normalToPressedAnimation);
		colorAnimation->setDuration(_animationDuration);
		colorAnimation->setEndValue(_colorPressed);
		QObject::connect(colorAnimation, &QVariantAnimation::valueChanged, this, [this](const QVariant& value) {
			if (_shadow) {
				const auto newValue = value.value<QColor>();
				_shadow->setColor(newValue);
			}
		});

		normalToPressedAnimation->addAnimation(blurAnimation);
		normalToPressedAnimation->addAnimation(colorAnimation);

		normalToPressedTransition->addAnimation(normalToPressedAnimation);
		QObject::connect(normalToPressedTransition, &QAbstractTransition::triggered, normalToPressedAnimation,
			[this, normalToPressedAnimation, blurAnimation, colorAnimation]() {
				blurAnimation->setStartValue(static_cast<int>(_shadow->blurRadius()));
				colorAnimation->setStartValue(_shadow->color());
				normalToPressedAnimation->start();
			});
	}

	// Pressed->Normal
	auto pressedToNormalTransition = statePressed->addTransition(_button, &QAbstractButton::released, stateNormal);
	{
		auto pressedToNormalAnimation = new QParallelAnimationGroup(_stateMachine);

		auto blurAnimation = new QVariantAnimation(pressedToNormalAnimation);
		blurAnimation->setDuration(_animationDuration);
		blurAnimation->setEndValue(_blurNormal);
		QObject::connect(blurAnimation, &QVariantAnimation::valueChanged, this, [this](const QVariant& value) {
			if (_shadow) {
				_shadow->setBlurRadius(value.toInt());
			}
		});

		auto colorAnimation = new QVariantAnimation(pressedToNormalAnimation);
		colorAnimation->setDuration(_animationDuration);
		colorAnimation->setEndValue(_colorNormal);
		QObject::connect(colorAnimation, &QVariantAnimation::valueChanged, this, [this](const QVariant& value) {
			if (_shadow) {
				_shadow->setColor(value.value<QColor>());
			}
		});

		pressedToNormalTransition->addAnimation(blurAnimation);
		pressedToNormalTransition->addAnimation(colorAnimation);

		pressedToNormalTransition->addAnimation(pressedToNormalAnimation);
		QObject::connect(pressedToNormalTransition, &QAbstractTransition::triggered, pressedToNormalAnimation,
			[this, pressedToNormalAnimation, blurAnimation, colorAnimation]() {
				if (_shadow) {
					blurAnimation->setStartValue(static_cast<int>(_shadow->blurRadius()));
					colorAnimation->setStartValue(_shadow->color());
					pressedToNormalAnimation->start();
				}
			});
	}

	_stateMachine->addState(stateNormal); // Takes ownership.
	_stateMachine->addState(statePressed); // Takes ownership.
	_stateMachine->setInitialState(stateNormal);
	_stateMachine->start();
}

void ButtonShadowBehavior::uninstall() {
	if (!_installed)
		return;

	_installed = false;

	_stateMachine.clear();
	_shadow.clear();
	_button->setGraphicsEffect(nullptr);
}

ButtonShadowBehavior.hpp

#pragma once

class ButtonShadowBehavior : public QObject {
	Q_OBJECT

public:
	explicit ButtonShadowBehavior(QAbstractButton* parent = nullptr);
	~ButtonShadowBehavior();

private:
	void install();
	void uninstall();

	bool _installed{ false };
	QPointer<QAbstractButton> _button{ nullptr };
	QPointer<QGraphicsDropShadowEffect> _shadow{ nullptr };
	QPointer<QStateMachine> _stateMachine{ nullptr };
	int _animationDuration{ 150 };
	double _blurNormal{ 8. };
	double _blurPressed{ 32. };
	QColor _colorNormal{ 0, 0, 0, 80 };
	QColor _colorPressed{ 0, 0, 0, 255 };
	QPointF _offset{ 0., 1. };
};