From 53e0c13be20c9986d52b385fd07f35504350a6de Mon Sep 17 00:00:00 2001
From: omar <omarcornut@gmail.com>
Date: Tue, 12 Mar 2019 20:57:02 +0100
Subject: [PATCH] TabBar: Reworked scrolling policy (when
 ImGuiTabBarFlags_FittingPolicyScroll is set) to teleport the view when aiming
 at a tab far away the visible section, and otherwise accelerate the scrolling
 speed to cap the scrolling time to 0.3 seconds.

---
 docs/CHANGELOG.txt |  3 +++
 imgui_internal.h   |  2 ++
 imgui_widgets.cpp  | 25 +++++++++++++++++++++----
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 6ecd1eb7..31af0bfa 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -77,6 +77,9 @@ Other Changes:
   scrolling policy enabled) or if is currently appearing.
 - TabBar: Fixed Tab tooltip code making drag and drop tooltip disappear during the frame where
   the drag payload activate a tab.
+- TabBar: Reworked scrolling policy (when ImGuiTabBarFlags_FittingPolicyScroll is set) to
+  teleport the view when aiming at a tab far away the visible section, and otherwise accelerate
+  the scrolling speed to cap the scrolling time to 0.3 seconds.
 - Text: Fixed large Text/TextUnformatted call not declaring its size when starting below the
   lower point of the current clipping rectangle. Somehow this bug has been there since v1.0!
   It was hardly noticeable but would affect the scrolling range, which in turn would affect
diff --git a/imgui_internal.h b/imgui_internal.h
index 9132551a..089ca2e1 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -1340,6 +1340,8 @@ struct ImGuiTabBar
     float               OffsetNextTab;          // Distance from BarRect.Min.x, incremented with each BeginTabItem() call, not used if ImGuiTabBarFlags_Reorderable if set.
     float               ScrollingAnim;
     float               ScrollingTarget;
+    float               ScrollingTargetDistToVisibility;
+    float               ScrollingSpeed;
     ImGuiTabBarFlags    Flags;
     ImGuiID             ReorderRequestTabId;
     int                 ReorderRequestDir;
diff --git a/imgui_widgets.cpp b/imgui_widgets.cpp
index 6d2ccc9c..6ff81177 100644
--- a/imgui_widgets.cpp
+++ b/imgui_widgets.cpp
@@ -6064,7 +6064,7 @@ ImGuiTabBar::ImGuiTabBar()
     CurrFrameVisible = PrevFrameVisible = -1;
     ContentsHeight = 0.0f;
     OffsetMax = OffsetNextTab = 0.0f;
-    ScrollingAnim = ScrollingTarget = 0.0f;
+    ScrollingAnim = ScrollingTarget = ScrollingTargetDistToVisibility = ScrollingSpeed = 0.0f;
     Flags = ImGuiTabBarFlags_None;
     ReorderRequestTabId = 0;
     ReorderRequestDir = 0;
@@ -6358,9 +6358,19 @@ static void ImGui::TabBarLayout(ImGuiTabBar* tab_bar)
             TabBarScrollToTab(tab_bar, scroll_track_selected_tab);
     tab_bar->ScrollingAnim = TabBarScrollClamp(tab_bar, tab_bar->ScrollingAnim);
     tab_bar->ScrollingTarget = TabBarScrollClamp(tab_bar, tab_bar->ScrollingTarget);
-    const float scrolling_speed = (tab_bar->PrevFrameVisible + 1 < g.FrameCount) ? FLT_MAX : (g.IO.DeltaTime * g.FontSize * 70.0f);
     if (tab_bar->ScrollingAnim != tab_bar->ScrollingTarget)
-        tab_bar->ScrollingAnim = ImLinearSweep(tab_bar->ScrollingAnim, tab_bar->ScrollingTarget, scrolling_speed);
+    {
+        // Scrolling speed adjust itself so we can always reach our target in 1/3 seconds.
+        // Teleport if we are aiming far off the visible line
+        tab_bar->ScrollingSpeed = ImMax(tab_bar->ScrollingSpeed, 70.0f * g.FontSize);
+        tab_bar->ScrollingSpeed = ImMax(tab_bar->ScrollingSpeed, ImFabs(tab_bar->ScrollingTarget - tab_bar->ScrollingAnim) / 0.3f);
+        const bool teleport = (tab_bar->PrevFrameVisible + 1 < g.FrameCount) || (tab_bar->ScrollingTargetDistToVisibility > 10.0f * g.FontSize);
+        tab_bar->ScrollingAnim = teleport ? tab_bar->ScrollingTarget : ImLinearSweep(tab_bar->ScrollingAnim, tab_bar->ScrollingTarget, g.IO.DeltaTime * tab_bar->ScrollingSpeed);
+    }
+    else
+    {
+        tab_bar->ScrollingSpeed = 0.0f;
+    }
 
     // Clear name buffers
     if ((tab_bar->Flags & ImGuiTabBarFlags_DockNode) == 0)
@@ -6438,10 +6448,17 @@ static void ImGui::TabBarScrollToTab(ImGuiTabBar* tab_bar, ImGuiTabItem* tab)
     int order = tab_bar->GetTabOrder(tab);
     float tab_x1 = tab->Offset + (order > 0 ? -margin : 0.0f);
     float tab_x2 = tab->Offset + tab->Width + (order + 1 < tab_bar->Tabs.Size ? margin : 1.0f);
+    tab_bar->ScrollingTargetDistToVisibility = 0.0f;
     if (tab_bar->ScrollingTarget > tab_x1)
+    {
+        tab_bar->ScrollingTargetDistToVisibility = ImMax(tab_bar->ScrollingAnim - tab_x2, 0.0f);
         tab_bar->ScrollingTarget = tab_x1;
-    if (tab_bar->ScrollingTarget + tab_bar->BarRect.GetWidth() < tab_x2)
+    }
+    else if (tab_bar->ScrollingTarget < tab_x2 - tab_bar->BarRect.GetWidth())
+    {
+        tab_bar->ScrollingTargetDistToVisibility = ImMax((tab_x1 - tab_bar->BarRect.GetWidth()) - tab_bar->ScrollingAnim, 0.0f);
         tab_bar->ScrollingTarget = tab_x2 - tab_bar->BarRect.GetWidth();
+    }
 }
 
 void ImGui::TabBarQueueChangeTabOrder(ImGuiTabBar* tab_bar, const ImGuiTabItem* tab, int dir)