Windows: BeginChild(): Resize borders rendered even when ImGuiWindowFlags_NoBackground is specified. (#1710, #7194)

docs/CHANGELOG.txt

@@ -56,6 +56,8 @@ Other changes:
 
 - Windows: BeginChild(): Fixed auto-resizing erroneously limiting size to host viewport
   minus padding. There are no limit to a child width/height. (#7063) [@Devyre]
+- Windows: BeginChild(): Resize borders rendered even when ImGuiWindowFlags_NoBackground
+  is specified. (#1710, #7194)
 - Windows: Fixed some auto-resizing path using style.WindowMinSize.x (instead of x/y)
   for both axises since 1.90. (#7106) [@n0bodysec]
 - Scrolling: internal scrolling value is rounded instead of truncated, as a way to reduce

imgui.cpp

@@ -6082,28 +6082,40 @@ static inline void ClampWindowPos(ImGuiWindow* window, const ImRect& visibility_
     window->Pos = ImClamp(window->Pos, visibility_rect.Min - size_for_clamping, visibility_rect.Max);
 }
 
+static void RenderWindowOuterSingleBorder(ImGuiWindow* window, int border_n, ImU32 border_col, float border_size)
+{
+    const ImGuiResizeBorderDef& def = resize_border_def[border_n];
+    const float rounding = window->WindowRounding;
+    const ImRect border_r = GetResizeBorderRect(window, border_n, rounding, 0.0f);
+    window->DrawList->PathArcTo(ImLerp(border_r.Min, border_r.Max, def.SegmentN1) + ImVec2(0.5f, 0.5f) + def.InnerDir * rounding, rounding, def.OuterAngle - IM_PI * 0.25f, def.OuterAngle);
+    window->DrawList->PathArcTo(ImLerp(border_r.Min, border_r.Max, def.SegmentN2) + ImVec2(0.5f, 0.5f) + def.InnerDir * rounding, rounding, def.OuterAngle, def.OuterAngle + IM_PI * 0.25f);
+    window->DrawList->PathStroke(border_col, ImDrawFlags_None, border_size);
+}
+
 static void ImGui::RenderWindowOuterBorders(ImGuiWindow* window)
 {
     ImGuiContext& g = *GImGui;
-    float rounding = window->WindowRounding;
-    float border_size = window->WindowBorderSize;
-    if (border_size > 0.0f && !(window->Flags & ImGuiWindowFlags_NoBackground))
-        window->DrawList->AddRect(window->Pos, window->Pos + window->Size, GetColorU32(ImGuiCol_Border), rounding, 0, border_size);
-
+    const float border_size = window->WindowBorderSize;
+    const ImU32 border_col = GetColorU32(ImGuiCol_Border);
+    if (border_size > 0.0f && (window->Flags & ImGuiWindowFlags_NoBackground) == 0)
+        window->DrawList->AddRect(window->Pos, window->Pos + window->Size, border_col, window->WindowRounding, 0, window->WindowBorderSize);
+    else if (border_size > 0.0f)
+    {
+        if (window->ChildFlags & ImGuiChildFlags_ResizeX) // Similar code as 'resize_border_mask' computation in UpdateWindowManualResize() but we specifically only always draw explicit child resize border.
+            RenderWindowOuterSingleBorder(window, 1, border_col, border_size);
+        if (window->ChildFlags & ImGuiChildFlags_ResizeY)
+            RenderWindowOuterSingleBorder(window, 3, border_col, border_size);
+    }
     if (window->ResizeBorderHovered != -1 || window->ResizeBorderHeld != -1)
     {
         const int border_n = (window->ResizeBorderHeld != -1) ? window->ResizeBorderHeld : window->ResizeBorderHovered;
-        const ImGuiResizeBorderDef& def = resize_border_def[border_n];
-        const ImRect border_r = GetResizeBorderRect(window, border_n, rounding, 0.0f);
-        const ImU32 border_col = GetColorU32((window->ResizeBorderHeld != -1) ? ImGuiCol_SeparatorActive : ImGuiCol_SeparatorHovered);
-        window->DrawList->PathArcTo(ImLerp(border_r.Min, border_r.Max, def.SegmentN1) + ImVec2(0.5f, 0.5f) + def.InnerDir * rounding, rounding, def.OuterAngle - IM_PI * 0.25f, def.OuterAngle);
-        window->DrawList->PathArcTo(ImLerp(border_r.Min, border_r.Max, def.SegmentN2) + ImVec2(0.5f, 0.5f) + def.InnerDir * rounding, rounding, def.OuterAngle, def.OuterAngle + IM_PI * 0.25f);
-        window->DrawList->PathStroke(border_col, 0, ImMax(2.0f, border_size)); // Thicker than usual
+        const ImU32 border_col_resizing = GetColorU32((window->ResizeBorderHeld != -1) ? ImGuiCol_SeparatorActive : ImGuiCol_SeparatorHovered);
+        RenderWindowOuterSingleBorder(window, border_n, border_col_resizing, ImMax(2.0f, window->WindowBorderSize)); // Thicker than usual
     }
     if (g.Style.FrameBorderSize > 0 && !(window->Flags & ImGuiWindowFlags_NoTitleBar))
     {
         float y = window->Pos.y + window->TitleBarHeight() - 1;
-        window->DrawList->AddLine(ImVec2(window->Pos.x + border_size, y), ImVec2(window->Pos.x + window->Size.x - border_size, y), GetColorU32(ImGuiCol_Border), g.Style.FrameBorderSize);
+        window->DrawList->AddLine(ImVec2(window->Pos.x + border_size, y), ImVec2(window->Pos.x + window->Size.x - border_size, y), border_col, g.Style.FrameBorderSize);
     }
 }