Fix popup and tooltip positioning when not fitting in the screen. Amend fa42ccea8.

# Conflicts:
#	docs/CHANGELOG.txt

docs/CHANGELOG.txt

@@ -68,6 +68,8 @@ Other Changes:
   tabs reordered in the tab list popup. [@Xipiryon]
 - Columns: Fix inverted ClipRect being passed to renderer when using certain primitives inside of
   a fully clipped column. (#3475) [@szreder]
+- Popups, Tooltips: Fix edge cases issues with positionning popups and tooltips when they are larger than
+  viewport on either or both axises. [@Rokups]
 - Metrics: Various tweaks, listing windows front-to-back, greying inactive items when possible.
 - Demo: Add simple InputText() callbacks demo (aside from the more elaborate ones in 'Examples->Console').
 - Backends: OpenGL3: Fix to avoid compiling/calling glBindSampler() on ES or pre 3.3 contexts which have 

docs/TODO.txt

@@ -219,7 +219,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - popups/modals: although it is sometimes convenient that popups/modals lifetime is owned by imgui, we could also a bool-owned-by-user api as long as Begin() return value testing is enforced.
 
  - tooltip: drag and drop with tooltip near monitor edges lose/changes its last direction instead of locking one. The drag and drop tooltip should always follow without changing direction.
- - tooltip: tooltip that doesn't fit in entire screen seems to lose their "last preferred direction" and may teleport when moving mouse.
  - tooltip: allow to set the width of a tooltip to allow TextWrapped() etc. while keeping the height automatic.
  - tooltip: tooltips with delay timers? or general timer policy? (instantaneous vs timed): IsItemHovered() with timer + implicit aabb-id for items with no ID. (#1485)
  - tooltip: drag tooltip hovering over source widget with IsItemHovered/SetTooltip flickers.

imgui.cpp

@@ -8007,37 +8007,47 @@ ImVec2 ImGui::FindBestWindowPosForPopupEx(const ImVec2& ref_pos, const ImVec2& s
         }
     }
 
-    // Default popup policy
+    // Tooltip and Default popup policy
+    // (Always first try the direction we used on the last frame, if any)
+    if (policy == ImGuiPopupPositionPolicy_Tooltip || policy == ImGuiPopupPositionPolicy_Default)
+    {
         const ImGuiDir dir_prefered_order[ImGuiDir_COUNT] = { ImGuiDir_Right, ImGuiDir_Down, ImGuiDir_Up, ImGuiDir_Left };
         for (int n = (*last_dir != ImGuiDir_None) ? -1 : 0; n < ImGuiDir_COUNT; n++)
         {
             const ImGuiDir dir = (n == -1) ? *last_dir : dir_prefered_order[n];
             if (n != -1 && dir == *last_dir) // Already tried this direction?
                 continue;
-        float avail_w = (dir == ImGuiDir_Left ? r_avoid.Min.x : r_outer.Max.x) - (dir == ImGuiDir_Right ? r_avoid.Max.x : r_outer.Min.x);
-        float avail_h = (dir == ImGuiDir_Up ? r_avoid.Min.y : r_outer.Max.y) - (dir == ImGuiDir_Down ? r_avoid.Max.y : r_outer.Min.y);
 
-        // There is no point in switching left/right sides when popup height exceeds available height or top/bottom
-        // sides when popup width exceeds available width.
-        if (avail_h < size.y && (dir == ImGuiDir_Up || dir == ImGuiDir_Down))
+            const float avail_w = (dir == ImGuiDir_Left ? r_avoid.Min.x : r_outer.Max.x) - (dir == ImGuiDir_Right ? r_avoid.Max.x : r_outer.Min.x);
+            const float avail_h = (dir == ImGuiDir_Up ? r_avoid.Min.y : r_outer.Max.y) - (dir == ImGuiDir_Down ? r_avoid.Max.y : r_outer.Min.y);
+
+            // If there not enough room on one axis, there's no point in positioning on a side on this axis (e.g. when not enough width, use a top/bottom position to maximize available width)
+            if (avail_w < size.x && (dir == ImGuiDir_Left || dir == ImGuiDir_Right))
                 continue;
-        else if (avail_w < size.x && (dir == ImGuiDir_Left || dir == ImGuiDir_Right))
+            if (avail_h < size.y && (dir == ImGuiDir_Up || dir == ImGuiDir_Down))
                 continue;
 
             ImVec2 pos;
             pos.x = (dir == ImGuiDir_Left) ? r_avoid.Min.x - size.x : (dir == ImGuiDir_Right) ? r_avoid.Max.x : base_pos_clamped.x;
             pos.y = (dir == ImGuiDir_Up) ? r_avoid.Min.y - size.y : (dir == ImGuiDir_Down) ? r_avoid.Max.y : base_pos_clamped.y;
 
-        // Clamp top-left (or top-right for RTL languages in the future) corner of popup to remain visible.
+            // Clamp top-left corner of popup
             pos.x = ImMax(pos.x, r_outer.Min.x);
             pos.y = ImMax(pos.y, r_outer.Min.y);
 
             *last_dir = dir;
             return pos;
         }
+    }
 
-    // Fallback, try to keep within display
+    // Fallback when not enough room:
     *last_dir = ImGuiDir_None;
+
+    // For tooltip we prefer avoiding the cursor at all cost even if it means that part of the tooltip won't be visible.
+    if (policy == ImGuiPopupPositionPolicy_Tooltip)
+        return ref_pos + ImVec2(2, 2); 
+
+    // Otherwise try to keep within display
     ImVec2 pos = ref_pos;
     pos.x = ImMax(ImMin(pos.x + size.x, r_outer.Max.x) - size.x, r_outer.Min.x);
     pos.y = ImMax(ImMin(pos.y + size.y, r_outer.Max.y) - size.y, r_outer.Min.y);
@@ -8070,12 +8080,12 @@ ImVec2 ImGui::FindBestWindowPosForPopup(ImGuiWindow* window)
             r_avoid = ImRect(-FLT_MAX, parent_window->ClipRect.Min.y, FLT_MAX, parent_window->ClipRect.Max.y); // Avoid parent menu-bar. If we wanted multi-line menu-bar, we may instead want to have the calling window setup e.g. a NextWindowData.PosConstraintAvoidRect field
         else
             r_avoid = ImRect(parent_window->Pos.x + horizontal_overlap, -FLT_MAX, parent_window->Pos.x + parent_window->Size.x - horizontal_overlap - parent_window->ScrollbarSizes.x, FLT_MAX);
-        return FindBestWindowPosForPopupEx(window->Pos, window->Size, &window->AutoPosLastDirection, r_outer, r_avoid);
+        return FindBestWindowPosForPopupEx(window->Pos, window->Size, &window->AutoPosLastDirection, r_outer, r_avoid, ImGuiPopupPositionPolicy_Default);
     }
     if (window->Flags & ImGuiWindowFlags_Popup)
     {
         ImRect r_avoid = ImRect(window->Pos.x - 1, window->Pos.y - 1, window->Pos.x + 1, window->Pos.y + 1);
-        return FindBestWindowPosForPopupEx(window->Pos, window->Size, &window->AutoPosLastDirection, r_outer, r_avoid);
+        return FindBestWindowPosForPopupEx(window->Pos, window->Size, &window->AutoPosLastDirection, r_outer, r_avoid, ImGuiPopupPositionPolicy_Default);
     }
     if (window->Flags & ImGuiWindowFlags_Tooltip)
     {
@@ -8087,10 +8097,7 @@ ImVec2 ImGui::FindBestWindowPosForPopup(ImGuiWindow* window)
             r_avoid = ImRect(ref_pos.x - 16, ref_pos.y - 8, ref_pos.x + 16, ref_pos.y + 8);
         else
             r_avoid = ImRect(ref_pos.x - 16, ref_pos.y - 8, ref_pos.x + 24 * sc, ref_pos.y + 24 * sc); // FIXME: Hard-coded based on mouse cursor shape expectation. Exact dimension not very important.
-        ImVec2 pos = FindBestWindowPosForPopupEx(ref_pos, window->Size, &window->AutoPosLastDirection, r_outer, r_avoid);
-        if (window->AutoPosLastDirection == ImGuiDir_None)
-            pos = ref_pos + ImVec2(2, 2); // If there's not enough room, for tooltip we prefer avoiding the cursor at all cost even if it means that part of the tooltip won't be visible.
-        return pos;
+        return FindBestWindowPosForPopupEx(ref_pos, window->Size, &window->AutoPosLastDirection, r_outer, r_avoid, ImGuiPopupPositionPolicy_Tooltip);
     }
     IM_ASSERT(0);
     return window->Pos;

imgui_internal.h

@@ -777,7 +777,8 @@ enum ImGuiNavLayer
 enum ImGuiPopupPositionPolicy
 {
     ImGuiPopupPositionPolicy_Default,
-    ImGuiPopupPositionPolicy_ComboBox
+    ImGuiPopupPositionPolicy_ComboBox,
+    ImGuiPopupPositionPolicy_Tooltip
 };
 
 struct ImGuiDataTypeTempStorage
@@ -1879,7 +1880,7 @@ namespace ImGui
     IMGUI_API void          BeginTooltipEx(ImGuiWindowFlags extra_flags, ImGuiTooltipFlags tooltip_flags);
     IMGUI_API ImGuiWindow*  GetTopMostPopupModal();
     IMGUI_API ImVec2        FindBestWindowPosForPopup(ImGuiWindow* window);
-    IMGUI_API ImVec2        FindBestWindowPosForPopupEx(const ImVec2& ref_pos, const ImVec2& size, ImGuiDir* last_dir, const ImRect& r_outer, const ImRect& r_avoid, ImGuiPopupPositionPolicy policy = ImGuiPopupPositionPolicy_Default);
+    IMGUI_API ImVec2        FindBestWindowPosForPopupEx(const ImVec2& ref_pos, const ImVec2& size, ImGuiDir* last_dir, const ImRect& r_outer, const ImRect& r_avoid, ImGuiPopupPositionPolicy policy);
 
     // Gamepad/Keyboard Navigation
     IMGUI_API void          NavInitWindow(ImGuiWindow* window, bool force_reinit);