dep/imgui: Fix smooth scrolling on scrollbar drag

dep/imgui/include/imgui_internal.h

@@ -2255,6 +2255,7 @@ struct ImGuiContext
     ImGuiComboPreviewData   ComboPreviewData;
     ImRect                  WindowResizeBorderExpectedRect;     // Expected border rect, switch to relative edit if moving
     bool                    WindowResizeRelativeMode;
+    unsigned char           ScrollbarHeld;                      // Is the scrollbar scrolling the window?
     short                   ScrollbarSeekMode;                  // 0: relative, -1/+1: prev/next page.
     float                   ScrollbarClickDeltaToGrabCenter;    // Distance between mouse and center of grab box, normalized in parent space. Use storage?
     float                   SliderGrabClickOffset;
@@ -2478,6 +2479,7 @@ struct ImGuiContext
         ColorEditSavedHue = ColorEditSavedSat = 0.0f;
         ColorEditSavedColor = 0;
         WindowResizeRelativeMode = false;
+        ScrollbarHeld = false;
         ScrollbarSeekMode = 0;
         ScrollbarClickDeltaToGrabCenter = 0.0f;
         SliderGrabClickOffset = 0.0f;

dep/imgui/src/imgui.cpp

@@ -4792,6 +4792,7 @@ void ImGui::NewFrame()
     g.HoveredId = 0;
     g.HoveredIdAllowOverlap = false;
     g.HoveredIdIsDisabled = false;
+    g.ScrollbarHeld >>= 1;
 
     // Clear ActiveID if the item is not alive anymore.
     // In 1.87, the common most call to KeepAliveID() was moved from GetID() to ItemAdd().
@@ -10802,7 +10803,7 @@ static ImVec2 CalcNextScrollFromScrollTargetAndClamp(ImGuiWindow* window)
             else
                 scroll[axis] -= ImMin(-diff, (-diff / (style.ScrollSmooth * multiplier)));
 
-            scroll[axis] = window->Appearing ? window->ScrollExpected[axis] : scroll[axis];
+            scroll[axis] = (window->Appearing || g.ScrollbarHeld & 1) ? window->ScrollExpected[axis] : scroll[axis];
         }
     }
     return scroll;

dep/imgui/src/imgui_widgets.cpp

@@ -1001,7 +1001,7 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS6
         {
             // On initial click calculate the distance between mouse and the center of the grab
             g.ScrollbarSeekMode = (short)held_dir;
-            g.ScrollbarClickDeltaToGrabCenter = (g.ScrollbarSeekMode == 0.0f) ? clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f : 0.0f;
+            g.ScrollbarClickDeltaToGrabCenter = (g.ScrollbarSeekMode == 0) ? clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f : 0.0f;
         }
 
         // Apply scroll (p_scroll_v will generally point on one member of window->Scroll)
@@ -1025,6 +1025,7 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS6
         // Update values for rendering
         scroll_ratio = ImSaturate((float)*p_scroll_v / (float)scroll_max);
         grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v;
+        g.ScrollbarHeld |= 2;
 
         // Update distance to grab now that we have seek'ed and saturated
         //if (seek_absolute)