ImGuiFullscreen: Allow smooth scrolling

dep/imgui/include/imgui.h

@@ -1717,6 +1717,7 @@ enum ImGuiStyleVar_
     ImGuiStyleVar_SeparatorTextBorderSize,  // float     SeparatorTextBorderSize
     ImGuiStyleVar_SeparatorTextAlign,       // ImVec2    SeparatorTextAlign
     ImGuiStyleVar_SeparatorTextPadding,     // ImVec2    SeparatorTextPadding
+    ImGuiStyleVar_ScrollSmooth,             // float     ScrollSmooth
     ImGuiStyleVar_COUNT
 };
 
@@ -2180,6 +2181,8 @@ struct ImGuiStyle
     ImGuiHoveredFlags HoverFlagsForTooltipMouse;// Default flags when using IsItemHovered(ImGuiHoveredFlags_ForTooltip) or BeginItemTooltip()/SetItemTooltip() while using mouse.
     ImGuiHoveredFlags HoverFlagsForTooltipNav;  // Default flags when using IsItemHovered(ImGuiHoveredFlags_ForTooltip) or BeginItemTooltip()/SetItemTooltip() while using keyboard/gamepad.
 
+    float             ScrollSmooth;             // Smooth scrolling amount: 1.0f no smoothing. Anything above 1.0f will make the scroll delta more smooth.
+
     IMGUI_API ImGuiStyle();
     IMGUI_API void ScaleAllSizes(float scale_factor);
 };

dep/imgui/include/imgui_internal.h

@@ -2618,7 +2618,8 @@ struct IMGUI_API ImGuiWindow
     ImGuiID                 MoveId;                             // == window->GetID("#MOVE")
     ImGuiID                 ChildId;                            // ID of corresponding item in parent window (for navigation to return from child window to parent window)
     ImGuiID                 PopupId;                            // ID in the popup stack when this window is used as a popup/menu (because we use generic Name/ID for recycling)
-    ImVec2                  Scroll;
+    ImVec2                  Scroll;                             // Current Visible Scroll position
+    ImVec2                  ScrollExpected;                     // Current Expected Scroll position
     ImVec2                  ScrollMax;
     ImVec2                  ScrollTarget;                       // target scroll position. stored as cursor position with scrolling canceled out, so the highest point is always 0.0f. (FLT_MAX for no change)
     ImVec2                  ScrollTargetCenterRatio;            // 0.0f = scroll so that target position is at top, 0.5f = scroll so that target position is centered