Selectable: Fixed highlight/hit extent when used with horizontal scrolling (in or outside columns). (#3187, #3386)

# Conflicts:
#	imgui_widgets.cpp

docs/CHANGELOG.txt

@@ -49,6 +49,8 @@ Other Changes:
   clipping, more than 16 KB characters are visible in the same low-level ImDrawList::RenderText
   call. ImGui-level functions such as TextUnformatted() are not affected. This is quite rare
   but it will be addressed later). (#3349)
+- Selectable: Fixed highlight/hit extent when used with horizontal scrolling (in or outside columns). 
+  Also fixed related text clipping when used in a column after the first one. (#3187, #3386)
 - Scrolling: Avoid SetScroll, SetScrollFromPos functions from snapping on the edge of scroll
   limits when close-enough by (WindowPadding - ItemPadding), which was a tweak with too many
   side-effects. The behavior is still present in SetScrollHere functions as they are more explicitly

imgui.cpp

@@ -5898,6 +5898,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         window->WorkRect.Min.y = ImFloor(window->InnerRect.Min.y - window->Scroll.y + ImMax(window->WindowPadding.y, window->WindowBorderSize));
         window->WorkRect.Max.x = window->WorkRect.Min.x + work_rect_size_x;
         window->WorkRect.Max.y = window->WorkRect.Min.y + work_rect_size_y;
+        window->ParentWorkRect = window->WorkRect;
 
         // [LEGACY] Content Region
         // FIXME-OBSOLETE: window->ContentRegionRect.Max is currently very misleading / partly faulty, but some BeginChild() patterns relies on it.

imgui_internal.h

@@ -1015,7 +1015,7 @@ struct ImGuiColumns
     float               HostCursorMaxPosX;      // Backup of CursorMaxPos at the time of BeginColumns()
     ImRect              HostInitialClipRect;    // Backup of ClipRect at the time of BeginColumns()
     ImRect              HostBackupClipRect;     // Backup of ClipRect during PushColumnsBackground()/PopColumnsBackground()
-    ImRect              HostWorkRect;           // Backup of WorkRect at the time of BeginColumns()
+    ImRect              HostBackupParentWorkRect;//Backup of WorkRect at the time of BeginColumns()
     ImVector<ImGuiColumnData> Columns;
     ImDrawListSplitter  Splitter;
 
@@ -1612,7 +1612,8 @@ struct IMGUI_API ImGuiWindow
     ImRect                  OuterRectClipped;                   // == Window->Rect() just after setup in Begin(). == window->Rect() for root window.
     ImRect                  InnerRect;                          // Inner rectangle (omit title bar, menu bar, scroll bar)
     ImRect                  InnerClipRect;                      // == InnerRect shrunk by WindowPadding*0.5f on each side, clipped within viewport or parent clip rect.
-    ImRect                  WorkRect;                           // Cover the whole scrolling region, shrunk by WindowPadding*1.0f on each side. This is meant to replace ContentRegionRect over time (from 1.71+ onward).
+    ImRect                  WorkRect;                           // Initially covers the whole scrolling region. Reduced by containers e.g columns/tables when active. Shrunk by WindowPadding*1.0f on each side. This is meant to replace ContentRegionRect over time (from 1.71+ onward).
+    ImRect                  ParentWorkRect;                     // Backup of WorkRect before entering a container such as columns/tables. Used by e.g. SpanAllColumns functions to easily access. Stacked containers are responsible for maintaining this. // FIXME-WORKRECT: Could be a stack?
     ImRect                  ClipRect;                           // Current clipping/scissoring rectangle, evolve as we are using PushClipRect(), etc. == DrawList->clip_rect_stack.back().
     ImRect                  ContentRegionRect;                  // FIXME: This is currently confusing/misleading. It is essentially WorkRect but not handling of scrolling. We currently rely on it as right/bottom aligned sizing operation need some size to rely on.
     ImVec2ih                HitTestHoleSize;                    // Define an optional rectangular hole where mouse will pass-through the window.

imgui_widgets.cpp

@@ -5704,8 +5704,8 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
     ItemSize(size, 0.0f);
 
     // Fill horizontal space
-    const float min_x = (flags & ImGuiSelectableFlags_SpanAllColumns) ? window->ContentRegionRect.Min.x : pos.x;
-    const float max_x = (flags & ImGuiSelectableFlags_SpanAllColumns) ? window->ContentRegionRect.Max.x : GetContentRegionMaxAbs().x;
+    const float min_x = (flags & ImGuiSelectableFlags_SpanAllColumns) ? window->ParentWorkRect.Min.x : pos.x;
+    const float max_x = (flags & ImGuiSelectableFlags_SpanAllColumns) ? window->ParentWorkRect.Max.x : window->WorkRect.Max.x;
     if (size_arg.x == 0.0f || (flags & ImGuiSelectableFlags_SpanAvailWidth))
         size.x = ImMax(label_size.x, max_x - min_x);
 
@@ -7665,7 +7665,8 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiColumnsFlag
     columns->HostCursorPosY = window->DC.CursorPos.y;
     columns->HostCursorMaxPosX = window->DC.CursorMaxPos.x;
     columns->HostInitialClipRect = window->ClipRect;
-    columns->HostWorkRect = window->WorkRect;
+    columns->HostBackupParentWorkRect = window->ParentWorkRect;
+    window->ParentWorkRect = window->WorkRect;
 
     // Set state for first column
     // We aim so that the right-most column will have the same clipping width as other after being clipped by parent ClipRect
@@ -7845,7 +7846,8 @@ void ImGui::EndColumns()
     }
     columns->IsBeingResized = is_being_resized;
 
-    window->WorkRect = columns->HostWorkRect;
+    window->WorkRect = window->ParentWorkRect;
+    window->ParentWorkRect = columns->HostBackupParentWorkRect;
     window->DC.CurrentColumns = NULL;
     window->DC.ColumnsOffset.x = 0.0f;
     window->DC.CursorPos.x = IM_FLOOR(window->Pos.x + window->DC.Indent.x + window->DC.ColumnsOffset.x);