Fix thumbs not displayed in all thumbs view

CCBUG: 408556

src/timeline2/view/qml/ClipThumbs.qml

@@ -10,13 +10,15 @@ Row {
     visible: !isAudio
     opacity: parentTrack.isAudio || parentTrack.isHidden || clipStatus == ClipState.Disabled ? 0.2 : 1
     property int thumbWidth: container.height * 16.0/9.0
-    property int scrollStart: Math.max(0, scrollView.flickableItem.contentX / timeline.scaleFactor - clipRoot.modelStart)
-    property int scrollEnd: scrollStart + scrollView.viewport.width / timeline.scaleFactor
+    property int scrollStart: scrollView.flickableItem.contentX - clipRoot.modelStart * timeline.scaleFactor
+    property int scrollEnd: scrollStart + scrollView.viewport.width
+    property bool enableCache: clipRoot.itemType == ProducerType.Video || clipRoot.itemType == ProducerType.AV
 
     function reload() {
         clipRoot.baseThumbPath =''
         clipRoot.baseThumbPath = clipRoot.variableThumbs ? '' : 'image://thumbnail/' + clipRoot.binId + '/' + (clipRoot.isImage ? '#0' : '#')
     }
+
     Repeater {
         id: thumbRepeater
         // switching the model allows to have different view modes:
@@ -33,10 +35,10 @@ Row {
             height: container.height
             fillMode: Image.PreserveAspectFit
             asynchronous: true
-            cache: false
+            cache: enableCache
             property int currentFrame: Math.floor(clipRoot.inPoint + Math.round((index) * width / timeline.scaleFactor)* clipRoot.speed)
             horizontalAlignment: thumbRepeater.count < 3 ? (index == 0 ? Image.AlignLeft : Image.AlignRight) : Image.AlignLeft
-            source: thumbRepeater.count < 3 ? (index == 0 ? clipRoot.baseThumbPath + Math.floor(clipRoot.inPoint * clipRoot.speed) : clipRoot.baseThumbPath + Math.floor(clipRoot.outPoint * clipRoot.speed)) : (currentFrame + width / timeline.scaleFactor < thumbRow.scrollStart || currentFrame > thumbRow.scrollEnd) ? '' : clipRoot.baseThumbPath + currentFrame
+            source: thumbRepeater.count < 3 ? (index == 0 ? clipRoot.baseThumbPath + Math.floor(clipRoot.inPoint * clipRoot.speed) : clipRoot.baseThumbPath + Math.floor(clipRoot.outPoint * clipRoot.speed)) : (index * width < thumbRow.scrollStart - width || index * width > thumbRow.scrollEnd) ? '' : clipRoot.baseThumbPath + currentFrame
         }
     }
 }