Separator(): Altered end-points to use more standard boundaries. (#205, #4787, #1643, #759)

docs/CHANGELOG.txt

@@ -73,6 +73,20 @@ Other changes:
 - Nav: Tabbing always enable nav highlight when ImGuiConfigFlags_NavEnableKeyboard is set.
   Previously was inconsistent and only enabled when stepping through a non-input item.
   (#6802, #3092, #5759, #787)
+- Separator(): Altered end-points to use more standard boundaries. (#205, #4787, #1643)
+  - Left position is always current cursor X position.
+  - Right position is always work-rect rightmost edge.
+  - Effectively means that:
+    - A separator in the root of a window will end up a little more distant from edges
+      than previously (essentially following WindowPadding instead of clipping edges).
+    - A separator inside a table cell end up a little distance from edges instead of
+      touching them (essentially following CellPadding instead of clipping edges).
+    - Matches tree indentation (was not the case before).
+    - Matches SeparatorText(). (#1643)
+    - Makes things correct inside groups without specific/hard-coded handling. (#205)
+  - Mostly legacy behavior when used inside old Columns(), as we favored that idiom back then,
+    only different is left position follows indentation level, to match calling a Separator()
+    inside or outside Columns().
 - Tables: Fixed an edge-case when no columns are visible + table scrollbar is visible + user
   code is always testing return value of TableSetColumnIndex() to coarse clip. With an active
   clipper it would have asserted. Without a clipper, the scrollbar range would be wrong.

docs/TODO.txt

@@ -126,7 +126,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
 
  - separator: expose flags (#759)
  - separator: take indent into consideration (optional)
- - separator: width, thickness, centering (#1643)
+ - separator: width, thickness, centering (#1643, #2657)
  - splitter: formalize the splitter idiom into an official api (we want to handle n-way split) (#319)
 
  - docking: merge docking branch (#2109)

imgui_widgets.cpp

@@ -1414,26 +1414,19 @@ void ImGui::SeparatorEx(ImGuiSeparatorFlags flags, float thickness)
     else if (flags & ImGuiSeparatorFlags_Horizontal)
     {
         // Horizontal Separator
-        float x1 = window->Pos.x;
+        float x1 = window->DC.CursorPos.x;
-        float x2 = window->Pos.x + window->Size.x;
+        float x2 = window->WorkRect.Max.x;
-
-        // FIXME-WORKRECT: old hack (#205) until we decide of consistent behavior with WorkRect/Indent and Separator
-        if (g.GroupStack.Size > 0 && g.GroupStack.back().WindowID == window->ID)
-            x1 += window->DC.Indent.x;
-
-        // FIXME-WORKRECT: In theory we should simply be using WorkRect.Min.x/Max.x everywhere but it isn't aesthetically what we want,
-        // need to introduce a variant of WorkRect for that purpose. (#4787)
-        if (ImGuiTable* table = g.CurrentTable)
-        {
-            x1 = table->Columns[table->CurrentColumn].MinX;
-            x2 = table->Columns[table->CurrentColumn].MaxX;
-        }
 
+        // Preserve legacy behavior inside Columns()
         // Before Tables API happened, we relied on Separator() to span all columns of a Columns() set.
         // We currently don't need to provide the same feature for tables because tables naturally have border features.
         ImGuiOldColumns* columns = (flags & ImGuiSeparatorFlags_SpanAllColumns) ? window->DC.CurrentColumns : NULL;
         if (columns)
+        {
+            x1 = window->Pos.x + window->DC.Indent.x; // Used to be Pos.x before 2023/10/03
+            x2 = window->Pos.x + window->Size.x;
             PushColumnsBackground();
+        }
 
         // We don't provide our width to the layout so that it doesn't get feed back into AutoFit
         // FIXME: This prevents ->CursorMaxPos based bounding box evaluation from working (e.g. TableEndCell)