fix scrollbar jumping bug for qt style

Author: 6he

internal/backends/qt/qt_widgets/scrollview.rs

@@ -171,6 +171,7 @@ impl Item for NativeScrollView {
                     if new_control == SC_ScrollBarSlider {
                         data.pressed_x = pos as f32;
                         data.pressed_val = -value as f32;
+                        data.pressed_max = max as f32;
                     }
                     data.active_controls = new_control;
                     InputEventResult::GrabMouse
@@ -210,6 +211,17 @@ impl Item for NativeScrollView {
                 MouseEvent::Moved { .. } => {
                     if data.pressed != 0 && data.active_controls == SC_ScrollBarSlider {
                         let max = max as f32;
+
+                        // Update reference points when the size of the viewport changes to
+                        // avoid 'jumping' during scrolling.
+                        // This happens when the height estimate of a ListView changes after
+                        // new items are loaded.
+                        if data.pressed_max != max {
+                            data.pressed_x = pos as f32;
+                            data.pressed_val = -value as f32;
+                            data.pressed_max = max;
+                        }
+
                         let new_val = data.pressed_val
                             + ((pos as f32) - data.pressed_x) * (max + (page_size as f32))
                                 / size as f32;

internal/backends/qt/qt_widgets/slider.rs

@@ -17,6 +17,7 @@ pub(super) struct NativeSliderData {
     pub pressed: u8,
     pub pressed_x: f32,
     pub pressed_val: f32,
+    pub pressed_max: f32,
 }
 
 type FloatArg = (f32,);

internal/core/items/flickable.rs

@@ -442,7 +442,7 @@ impl FlickableData {
 
                     // Update reference points when the size of the viewport changes to
                     // avoid 'jumping' during scrolling.
-                    // This happens when height estimate of a ListView changes after
+                    // This happens when the height estimate of a ListView changes after
                     // new items are loaded.
                     if current_viewport_size != inner.pressed_viewport_size {
                         inner.pressed_viewport_size = current_viewport_size;