Fixed using SetNextWindowPos() on a child window (which wasn't really documented) position the cursor as expected in the parent window, so there is no mismatch between the layout in parent and the position of the child window. Demo tweak and adding some child window stuff

docs/CHANGELOG.txt

@@ -58,9 +58,12 @@ Other Changes:
   it only works _if_ the back-end sets ImGuiBackendFlags_HasMouseCursors, which the standard back-end do.
 - Window: Added io.ConfigWindowsMoveFromTitleBarOnly option. Still is ignored by window with no title bars (often popups).
   This affects clamping window within the visible area: with this option enabled title bars need to be visible. (#899)
+- Window: Fixed using SetNextWindowPos() on a child window (which wasn't really documented) position the cursor as expected
+  in the parent window, so there is no mismatch between the layout in parent and the position of the child window. 
 - Style: Tweaked default value of style.DisplayWindowPadding from (20,20) to (19,19) so the default style as a value
   which is the same as the title bar height.
 - Demo: "Simple Layout" and "Style Editor" are now using tabs.
+- Demo: Added a few more things under "Child windows" (changing ImGuiCol_ChildBg, positioning child, using IsItemHovered after a child).
 - Examples: DirectX10/11/12: Made imgui_impl_dx10/dx11/dx12.cpp link d3dcompiler.lib from the .cpp file
   to ease integration.
 

docs/TODO.txt

@@ -30,6 +30,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - window: GetWindowSize() returns (0,0) when not calculated? (#1045)
  - window: freeze window flag: if not focused/hovered, return false, render with previous ImDrawList. and/or reduce refresh rate. 
  - window: investigate better auto-positioning for new windows.
+ - window/child: the first draw command of a child window could be moved into the current draw command of the parent window (unless child+tooltip?).
  - scrolling: allow immediately effective change of scroll after Begin() if we haven't appended items yet.
  - scrolling/clipping: separator on the initial position of a window is not visible (cursorpos.y <= clippos.y). (2017-08-20: can't repro)
  - scrolling/style: shadows on scrollable areas to denote that there is more contents

imgui.cpp

@@ -4152,6 +4152,10 @@ static bool ImGui::BeginChildEx(const char* name, ImGuiID id, const ImVec2& size
     child_window->ChildId = id;
     child_window->AutoFitChildAxises = auto_fit_axises;
 
+    // Set the cursor to handle case where the user called SetNextWindowPos()+BeginChild() manually.
+    // While this is not really documented/defined, it seems that the expected thing to do.
+    parent_window->DC.CursorPos = child_window->Pos;
+
     // Process navigation-in immediately so NavInit can run on first frame
     if (g.NavActivateId == id && !(flags & ImGuiWindowFlags_NavFlattened) && (child_window->DC.NavLayerActiveMask != 0 || child_window->DC.NavHasScroll))
     {

imgui_demo.cpp

@@ -1488,7 +1488,7 @@ static void ShowDemoWindowWidgets()
             ImGui::IsWindowHovered(ImGuiHoveredFlags_AnyWindow));
 
         ImGui::BeginChild("child", ImVec2(0, 50), true);
-        ImGui::Text("This is another child window for testing with the _ChildWindows flag.");
+        ImGui::Text("This is another child window for testing the _ChildWindows flag.");
         ImGui::EndChild();
         if (embed_all_inside_a_child_window)
             ImGui::EndChild();
@@ -1521,8 +1521,9 @@ static void ShowDemoWindowLayout()
     if (!ImGui::CollapsingHeader("Layout"))
         return;
 
-    if (ImGui::TreeNode("Child regions"))
+    if (ImGui::TreeNode("Child windows"))
     {
+        ShowHelpMarker("Use child windows to begin into a self-contained independent scrolling/clipping regions within a host window.");
         static bool disable_mouse_wheel = false;
         static bool disable_menu = false;
         ImGui::Checkbox("Disable Mouse Wheel", &disable_mouse_wheel);
@@ -1537,7 +1538,8 @@ static void ShowDemoWindowLayout()
 
         // Child 1: no border, enable horizontal scrollbar
         {
-            ImGui::BeginChild("Child1", ImVec2(ImGui::GetWindowContentRegionWidth() * 0.5f, 300), false, ImGuiWindowFlags_HorizontalScrollbar | (disable_mouse_wheel ? ImGuiWindowFlags_NoScrollWithMouse : 0));
+            ImGuiWindowFlags window_flags = ImGuiWindowFlags_HorizontalScrollbar | (disable_mouse_wheel ? ImGuiWindowFlags_NoScrollWithMouse : 0);
+            ImGui::BeginChild("Child1", ImVec2(ImGui::GetWindowContentRegionWidth() * 0.5f, 260), false, window_flags);
             for (int i = 0; i < 100; i++)
             {
                 ImGui::Text("%04d: scrollable region", i);
@@ -1553,8 +1555,9 @@ static void ShowDemoWindowLayout()
 
         // Child 2: rounded border
         {
+            ImGuiWindowFlags window_flags = (disable_mouse_wheel ? ImGuiWindowFlags_NoScrollWithMouse : 0) | (disable_menu ? 0 : ImGuiWindowFlags_MenuBar);
             ImGui::PushStyleVar(ImGuiStyleVar_ChildRounding, 5.0f);
-            ImGui::BeginChild("Child2", ImVec2(0, 300), true, (disable_mouse_wheel ? ImGuiWindowFlags_NoScrollWithMouse : 0) | (disable_menu ? 0 : ImGuiWindowFlags_MenuBar));
+            ImGui::BeginChild("Child2", ImVec2(0, 260), true, window_flags);
             if (!disable_menu && ImGui::BeginMenuBar())
             {
                 if (ImGui::BeginMenu("Menu"))
@@ -1576,6 +1579,27 @@ static void ShowDemoWindowLayout()
             ImGui::PopStyleVar();
         }
 
+        ImGui::Separator();
+
+        // Demonstrate a few extra things
+        // - Changing ImGuiCol_ChildBg (which is transparent black in default styles)
+        // - Using SetCursorPos() to position the child window (because the child window is an item from the POV of the parent window)
+        //   You can also call SetNextWindowPos() to position the child window. The parent window will effectively layout from this position.
+        // - Using ImGui::GetItemRectMin/Max() to query the "item" state (because the child window is an item from the POV of the parent window)
+        //   See "Widgets" -> "Querying Status (Active/Focused/Hovered etc.)" section for more details about this.
+        {
+            ImGui::SetCursorPosX(50);
+            ImGui::PushStyleColor(ImGuiCol_ChildBg, IM_COL32(255, 0, 0, 100));
+            ImGui::BeginChild("blah", ImVec2(200, 100), true, ImGuiWindowFlags_None);
+            for (int n = 0; n < 50; n++)
+                ImGui::Text("Some test %d", n);
+            ImGui::EndChild();
+            ImVec2 child_rect_min = ImGui::GetItemRectMin();
+            ImVec2 child_rect_max = ImGui::GetItemRectMax();
+            ImGui::PopStyleColor();
+            ImGui::Text("Rect of child window is: (%.0f,%.0f) (%.0f,%.0f)", child_rect_min.x, child_rect_min.y, child_rect_max.x, child_rect_max.y);
+        }
+
         ImGui::TreePop();
     }
 
@@ -1819,7 +1843,7 @@ static void ShowDemoWindowLayout()
 
     if (ImGui::TreeNode("Text Baseline Alignment"))
     {
-        ImGui::TextWrapped("(This is testing the vertical alignment that occurs on text to keep it at the same baseline as widgets. Lines only composed of text or \"small\" widgets fit in less vertical spaces than lines with normal widgets)");
+        ShowHelpMarker("This is testing the vertical alignment that gets applied on text to keep it aligned with widgets. Lines only composed of text or \"small\" widgets fit in less vertical spaces than lines with normal widgets.");
 
         ImGui::Text("One\nTwo\nThree"); ImGui::SameLine();
         ImGui::Text("Hello\nWorld"); ImGui::SameLine();
@@ -1874,7 +1898,8 @@ static void ShowDemoWindowLayout()
 
     if (ImGui::TreeNode("Scrolling"))
     {
-        ImGui::TextWrapped("(Use SetScrollHereY() or SetScrollFromPosY() to scroll to a given position.)");
+        ShowHelpMarker("Use SetScrollHereY() or SetScrollFromPosY() to scroll to a given position.");
+
         static bool track = true;
         static int track_line = 50, scroll_to_px = 200;
         ImGui::Checkbox("Track", &track);
@@ -1915,8 +1940,7 @@ static void ShowDemoWindowLayout()
 
     if (ImGui::TreeNode("Horizontal Scrolling"))
     {
-        ImGui::Bullet(); ImGui::TextWrapped("Horizontal scrolling for a window has to be enabled explicitly via the ImGuiWindowFlags_HorizontalScrollbar flag.");
-        ImGui::Bullet(); ImGui::TextWrapped("You may want to explicitly specify content width by calling SetNextWindowContentWidth() before Begin().");
+        ShowHelpMarker("Horizontal scrolling for a window has to be enabled explicitly via the ImGuiWindowFlags_HorizontalScrollbar flag.\n\nYou may want to explicitly specify content width by calling SetNextWindowContentWidth() before Begin().");
         static int lines = 7;
         ImGui::SliderInt("Lines", &lines, 1, 15);
         ImGui::PushStyleVar(ImGuiStyleVar_FrameRounding, 3.0f);