Window: Fixed contents region being off by WindowBorderSize amount on the right when scrollbar is active.

docs/CHANGELOG.txt

@@ -58,6 +58,7 @@ Other Changes:
   One of the noticeable minor side effect was that navigating menus would have had a tendency to disable
   highlight from parent menu items earlier than necessary while approaching the child menu.
 - Window: Close button is horizontally aligned with style.FramePadding.x.
+- Window: Fixed contents region being off by WindowBorderSize amount on the right when scrollbar is active.
 - GetMouseDragDelta(): also returns the delta on the mouse button released frame. (#2419)
 - GetMouseDragDelta(): verify that mouse positions are valid otherwise returns zero.
 - Inputs: Also add support for horizontal scroll with Shift+Mouse Wheel. (#2424, #1463) [@LucaRood]

imgui.cpp

@@ -5414,8 +5414,8 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         // FIXME: window->ContentsRegionRect.Max is currently very misleading / partly faulty, but some BeginChild() patterns relies on it.
         window->ContentsRegionRect.Min.x = window->Pos.x - window->Scroll.x + window->WindowPadding.x;
         window->ContentsRegionRect.Min.y = window->Pos.y - window->Scroll.y + window->WindowPadding.y + window->TitleBarHeight() + window->MenuBarHeight();
-        window->ContentsRegionRect.Max.x = window->Pos.x - window->Scroll.x - window->WindowPadding.x + (window->SizeContentsExplicit.x != 0.0f ? window->SizeContentsExplicit.x : (window->Size.x - window->ScrollbarSizes.x));
-        window->ContentsRegionRect.Max.y = window->Pos.y - window->Scroll.y - window->WindowPadding.y + (window->SizeContentsExplicit.y != 0.0f ? window->SizeContentsExplicit.y : (window->Size.y - window->ScrollbarSizes.y));
+        window->ContentsRegionRect.Max.x = window->Pos.x - window->Scroll.x - window->WindowPadding.x + (window->SizeContentsExplicit.x != 0.0f ? window->SizeContentsExplicit.x : (window->Size.x - window->ScrollbarSizes.x + window->WindowBorderSize));
+        window->ContentsRegionRect.Max.y = window->Pos.y - window->Scroll.y - window->WindowPadding.y + (window->SizeContentsExplicit.y != 0.0f ? window->SizeContentsExplicit.y : (window->Size.y - window->ScrollbarSizes.y + window->WindowBorderSize));
 
         // Setup drawing context
         // (NB: That term "drawing context / DC" lost its meaning a long time ago. Initially was meant to hold transient data only. Nowadays difference between window-> and window->DC-> is dubious.)
@@ -5517,10 +5517,6 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             }
         }
 
-        // Save clipped aabb so we can access it in constant-time in FindHoveredWindow()
-        window->OuterRectClipped = window->Rect();
-        window->OuterRectClipped.ClipWith(window->ClipRect);
-
         // Pressing CTRL+C while holding on a window copy its content to the clipboard
         // This works but 1. doesn't handle multiple Begin/End pairs, 2. recursing into another Begin/End pair - so we need to work that out and add better logging scope.
         // Maybe we can support CTRL+C on every element?
@@ -5530,13 +5526,17 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
                 LogToClipboard();
         */
 
+        // Save clipped aabb so we can access it in constant-time in FindHoveredWindow()
+        window->OuterRectClipped = window->Rect();
+        window->OuterRectClipped.ClipWith(window->ClipRect);
+
         // Inner rectangle
         // We set this up after processing the resize grip so that our clip rectangle doesn't lag by a frame
         // Note that if our window is collapsed we will end up with an inverted (~null) clipping rectangle which is the correct behavior.
         window->InnerMainRect.Min.x = title_bar_rect.Min.x + window->WindowBorderSize;
         window->InnerMainRect.Min.y = title_bar_rect.Max.y + window->MenuBarHeight() + (((flags & ImGuiWindowFlags_MenuBar) || !(flags & ImGuiWindowFlags_NoTitleBar)) ? style.FrameBorderSize : window->WindowBorderSize);
-        window->InnerMainRect.Max.x = window->Pos.x + window->Size.x - window->ScrollbarSizes.x - window->WindowBorderSize;
-        window->InnerMainRect.Max.y = window->Pos.y + window->Size.y - window->ScrollbarSizes.y - window->WindowBorderSize;
+        window->InnerMainRect.Max.x = window->Pos.x + window->Size.x - ImMax(window->ScrollbarSizes.x, window->WindowBorderSize);
+        window->InnerMainRect.Max.y = window->Pos.y + window->Size.y - ImMax(window->ScrollbarSizes.y, window->WindowBorderSize);
         //window->DrawList->AddRect(window->InnerRect.Min, window->InnerRect.Max, IM_COL32_WHITE);
 
         // Inner clipping rectangle