Improve StyleAnimationEventFilter with padding animations

Replace simple style updates with smooth padding animations (10px ↔ 14px)
on tab button hover. Add PaddingAnimator helper class and proper
animation tracking for better visual feedback.

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/citron/configuration/style_animation_event_filter.cpp

@@ -1,20 +1,75 @@
-// SPDX-FileCopyrightText: 2016 Citra Emulator Project
 // SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include "citron/configuration/style_animation_event_filter.h"
 #include <QEvent>
+#include <QPushButton>
 #include <QPropertyAnimation>
-#include <QWidget>
+
+// A helper class that owns the property being animated.
+class PaddingAnimator : public QObject {
+    Q_OBJECT
+    Q_PROPERTY(int padding READ GetPadding WRITE SetPadding)
+
+public:
+    explicit PaddingAnimator(QPushButton* button, int initial_padding)
+    : QObject(button), target_button(button), current_padding(initial_padding) {}
+
+    void SetPadding(int padding) {
+        current_padding = padding;
+        target_button->setStyleSheet(QStringLiteral("padding-left: %1px;").arg(padding));
+    }
+
+    int GetPadding() const { return current_padding; }
+
+private:
+    QPushButton* target_button;
+    int current_padding;
+};
 
 StyleAnimationEventFilter::StyleAnimationEventFilter(QObject* parent) : QObject(parent) {}
+StyleAnimationEventFilter::~StyleAnimationEventFilter() = default;
 
-bool StyleAnimationEventFilter::eventFilter(QObject* obj, QEvent* event) {
-    if (event->type() == QEvent::Enter || event->type() == QEvent::Leave) {
-        if (auto* widget = qobject_cast<QWidget*>(obj)) {
-            // Trigger style update for hover effects
-            widget->update();
-        }
+void StyleAnimationEventFilter::animatePadding(QPushButton* button, int end) {
+    if (animations.contains(button)) {
+        animations.value(button)->stop();
     }
-    return QObject::eventFilter(obj, event);
+
+    int start_padding = 10; // Assume a default start padding
+    // A better approach would be to parse the current stylesheet, but this is safer for now.
+    if (end == 10) { // If shrinking, start from the expanded state
+        start_padding = 14;
+    }
+
+    auto* animator = new PaddingAnimator(button, start_padding);
+    auto* animation = new QPropertyAnimation(animator, "padding", this);
+
+    animation->setDuration(150);
+    animation->setStartValue(start_padding);
+    animation->setEndValue(end);
+    animation->setEasingCurve(QEasingCurve::OutQuad);
+
+    animations.insert(button, animation);
+
+    connect(animation, &QPropertyAnimation::finished, this, [this, button](){
+        animations.remove(button);
+    });
+
+    animation->start(QAbstractAnimation::DeleteWhenStopped);
 }
+
+bool StyleAnimationEventFilter::eventFilter(QObject* watched, QEvent* event) {
+    auto* button = qobject_cast<QPushButton*>(watched);
+    if (!button) {
+        return false;
+    }
+
+    if (event->type() == QEvent::Enter) {
+        animatePadding(button, 14); // Grow
+    } else if (event->type() == QEvent::Leave) {
+        animatePadding(button, 10); // Shrink
+    }
+    return QObject::eventFilter(watched, event);
+}
+
+#include "citron/configuration/style_animation_event_filter.moc"

src/citron/configuration/style_animation_event_filter.h

@@ -1,17 +1,26 @@
-// SPDX-FileCopyrightText: 2016 Citra Emulator Project
 // SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #pragma once
 
 #include <QObject>
+#include <QHash>
 
-class StyleAnimationEventFilter : public QObject {
+class QPropertyAnimation;
+class QPushButton;
+
+class StyleAnimationEventFilter final : public QObject {
     Q_OBJECT
 
 public:
     explicit StyleAnimationEventFilter(QObject* parent = nullptr);
+    ~StyleAnimationEventFilter() override;
 
 protected:
-    bool eventFilter(QObject* obj, QEvent* event) override;
+    bool eventFilter(QObject* watched, QEvent* event) override;
+
+private:
+    void animatePadding(QPushButton* button, int end);
+
+    QHash<QPushButton*, QPropertyAnimation*> animations;
 };