kcms/cursortheme: Make the cursor preview on hover animated again

I removed that feature when killing the X specific code just using
the pixmap setter in 9f4ad82c5b5c47f6e3a3ed78ce559de4db361c78 (plasma-desktop).
To make it work we can drive the animation ourselves.

kcms/cursortheme/xcursor/cursortheme.h

@@ -9,6 +9,8 @@
 #include <QHash>
 #include <QPixmap>
 
+#include <chrono>
+
 /**
  * This is the abstract base class for all cursor themes stored in a
  * CursorThemeModel and previewed in a PreviewWidget.
@@ -41,6 +43,11 @@ public:
         PendingDeletionRole,
     };
 
+    struct CursorImage {
+        QImage image;
+        std::chrono::milliseconds delay;
+    };
+
     CursorTheme()
     {
     }
@@ -97,6 +104,10 @@ public:
     /// If the theme doesn't have the cursor @p name, it should return a null image.
     virtual QImage loadImage(const QString &name, int size = 0) const = 0;
 
+    /// Loads the cursor images @p name, with the nominal size @p size.
+    /// The images should be autocropped to the smallest possible size.
+    /// If the theme doesn't have the cursor @p name, it should return an empty vector
+    virtual std::vector<CursorImage> loadImages(const QString &name, int size = 0) const = 0;
 
     /// Loads the cursor @p name, with the nominal size @p size.
     /// If the theme doesn't have the cursor @p name, it should return

kcms/cursortheme/xcursor/previewwidget.cpp

@@ -79,23 +79,25 @@ public:
     {
         return pixmap();
     }
-
+    const std::vector<CursorTheme::CursorImage> &images() const
+    {
+        return m_images;
+    }
 private:
     int m_boundingSize;
     QPixmap m_pixmap;
+    std::vector<CursorTheme::CursorImage> m_images;
     QPoint m_pos;
 };
 
 PreviewCursor::PreviewCursor(const CursorTheme *theme, const QString &name, int size)
     : m_boundingSize(size > 0 ? size : theme->defaultCursorSize())
+    , m_images(theme->loadImages(name, size))
 {
-    // Create the preview pixmap
-    QImage image = theme->loadImage(name, size);
-
-    if (image.isNull())
+    if (m_images.empty())
         return;
 
-    m_pixmap = QPixmap::fromImage(image);
+    m_pixmap = QPixmap::fromImage(m_images.front().image);
 }
 
 QRect PreviewCursor::rect() const
@@ -112,6 +114,11 @@ PreviewWidget::PreviewWidget(QQuickItem *parent)
 {
     setAcceptHoverEvents(true);
     current = nullptr;
+    connect(&m_animationTimer, &QTimer::timeout, this, [this] {
+        setCursor(QPixmap::fromImage(current->images().at(nextAnimationFrame).image));
+        m_animationTimer.setInterval(current->images().at(nextAnimationFrame).delay);
+        nextAnimationFrame = (nextAnimationFrame + 1) % current->images().size();
+    });
 }
 
 PreviewWidget::~PreviewWidget()
@@ -259,23 +266,35 @@ void PreviewWidget::hoverMoveEvent(QHoverEvent *e)
     if (needLayout)
         layoutItems();
 
-    for (const PreviewCursor *c : qAsConst(list)) {
-        if (c->rect().contains(e->pos())) {
-            if (c != current) {
-                setCursor(QCursor(c->pixmap()));
-                current = c;
-            }
-            return;
-        }
+    auto it = std::find_if(list.cbegin(), list.cend(), [e](const PreviewCursor *c) {
+        return c->rect().contains(e->pos());
+    });
+    const PreviewCursor *cursor = it != list.cend() ? *it : nullptr;
+
+    if (cursor == std::exchange(current, cursor)) {
+        return;
     }
+    m_animationTimer.stop();
 
-    setCursor(Qt::ArrowCursor);
-    current = nullptr;
+    if (current == nullptr) {
+        setCursor(Qt::ArrowCursor);
+        return;
+    }
+
+    if (current->images().size() <= 1) {
+        setCursor(current->pixmap());
+        return;
+    }
+
+    nextAnimationFrame = 0;
+    m_animationTimer.setInterval(0);
+    m_animationTimer.start();
 }
 
 void PreviewWidget::hoverLeaveEvent(QHoverEvent *e)
 {
     Q_UNUSED(e);
+    m_animationTimer.stop();
     unsetCursor();
 }
 

kcms/cursortheme/xcursor/previewwidget.h

@@ -9,6 +9,7 @@
 #include "sortproxymodel.h"
 #include <QPointer>
 #include <QQuickPaintedItem>
+#include <QTimer>
 
 class CursorTheme;
 class PreviewCursor;
@@ -63,4 +64,6 @@ private:
     QPointer<SortProxyModel> m_themeModel;
     int m_currentIndex;
     int m_currentSize;
+    QTimer m_animationTimer;
+    size_t nextAnimationFrame;
 };

kcms/cursortheme/xcursor/xcursortheme.cpp

@@ -209,3 +209,32 @@ QImage XCursorTheme::loadImage(const QString &name, int size) const
 
     return image;
 }
+
+std::vector<CursorTheme::CursorImage> XCursorTheme::loadImages(const QString &name, int size) const
+{
+    if (size <= 0)
+        size = defaultCursorSize();
+
+    // Load the images
+    XcursorImages *xcimages = xcLoadImages(name, size);
+
+    if (!xcimages)
+        xcimages = xcLoadImages(findAlternative(name), size);
+
+    if (!xcimages) {
+        return {};
+    }
+
+    std::vector<CursorImage> images;
+    images.reserve(xcimages->nimage);
+    for (int i = 0; i < xcimages->nimage; ++i) {
+        // Convert the XcursorImage to a QImage, and auto-crop it
+        const XcursorImage *xcimage = xcimages->images[i];
+        QImage image(reinterpret_cast<unsigned char *>(xcimage->pixels), xcimage->width, xcimage->height, QImage::Format_ARGB32_Premultiplied);
+        images.push_back(CursorImage{autoCropImage(image), std::chrono::milliseconds{xcimage->delay}});
+    }
+
+    XcursorImagesDestroy(xcimages);
+
+    return images;
+}

kcms/cursortheme/xcursor/xcursortheme.h

@@ -37,7 +37,9 @@ public:
     {
         return m_inherits;
     }
+
     QImage loadImage(const QString &name, int size = 0) const override;
+    std::vector<CursorImage> loadImages(const QString &name, int size = 0) const override;
     qulonglong loadCursor(const QString &name, int size = 0) const override;
 
     /** Returns the size that the XCursor library would use if no