informationpanelcontent: prevent repeated disabled effect on previews

When switching files quickly in the Information Panel, the preview pixmap could appear progressively brighter/whiter. This happened because markOutdatedPreview() was applying KIconEffect::toDisabled() multiple times on the same pixmap while a preview job was still pending.
This patch fixes the issue by:
- Tracking the URL that was last disabled, and only applying the disabled effect once per URL.
- Clearing the disabled state whenever a new preview job starts or when a new pixmap is shown.

With this change, the "disabled preview" effect is preserved (still useful for slow HDD or network filesystems), but the progressive white-out artifact no longer occurs when navigating rapidly.

BUG: 507844

2 files changed, 15 insertions, 2 deletions

diff --git a/src/panels/information/informationpanelcontent.cpp b/src/panels/information/informationpanelcontent.cpp
index db7117e5a..afca9a76c 100644
--- a/src/panels/information/informationpanelcontent.cpp
+++ b/src/panels/information/informationpanelcontent.cpp
@@ -172,6 +172,9 @@ void InformationPanelContent::refreshPixmapView()
         m_previewJob->kill();
     }
 
+    // Reset disabled state when starting a new preview job
+    m_disabledPreviewUrl.clear();
+
     // try to get a preview pixmap from the item...
 
     // Mark the currently shown preview as outdated. This is done
@@ -362,6 +365,7 @@ void InformationPanelContent::showIcon(const KFileItem &item)
     QPixmap pixmap = KIconUtils::addOverlays(icon, item.overlays()).pixmap(m_preview->size(), devicePixelRatioF());
     pixmap.setDevicePixelRatio(devicePixelRatioF());
     m_preview->setPixmap(pixmap);
+    m_disabledPreviewUrl.clear();
 }
 
 void InformationPanelContent::showPreview(const KFileItem &item, const QPixmap &pixmap)
@@ -434,9 +438,17 @@ void InformationPanelContent::markOutdatedPreview()
         // use it until the preview is done
         showIcon(m_item);
     } else {
+        // Only apply disabled effect once per URL to avoid repeated brightening
+        if (m_disabledPreviewUrl == m_item.url()) {
+            return;
+        }
+        m_disabledPreviewUrl = m_item.url();
+
         QPixmap disabledPixmap = m_preview->pixmap();
-        KIconEffect::toDisabled(disabledPixmap);
-        m_preview->setPixmap(disabledPixmap);
+        if (!disabledPixmap.isNull()) {
+            KIconEffect::toDisabled(disabledPixmap);
+            m_preview->setPixmap(disabledPixmap);
+        }
     }
 }
 
diff --git a/src/panels/information/informationpanelcontent.h b/src/panels/information/informationpanelcontent.h
index 58adfb9c0..e305eddde 100644
--- a/src/panels/information/informationpanelcontent.h
+++ b/src/panels/information/informationpanelcontent.h
@@ -154,6 +154,7 @@ private:
     QDialogButtonBox *m_configureButtons;
 
     bool m_isVideo;
+    QUrl m_disabledPreviewUrl;
 };
 
 #endif // INFORMATIONPANELCONTENT_H