Windows: BeginChild(): fixed auto-fit calculation when using either (not both) ResizeX/ResizeY and double-clicking on a border. (#1710)

Calculation incorrectly didn't always account for scrollbar as it assumed the other axis would also be auto-fit.

docs/CHANGELOG.txt

@@ -56,6 +56,10 @@ Breaking changes:
 
 Other changes:
 
+- Windows: BeginChild(): fixed visibility of fully clipped child windows and tables to Test Engine.
+- Windows: BeginChild(): fixed auto-fit calculation when using either (not both) ResizeX/ResizeY
+  and double-clicking on a border. Calculation incorrectly didn't always account for scrollbar as
+  it assumed the other axis would also be auto-fit. (#1710)
 - Inputs: added Shortcut() function (w/ routing policies) in public API. (#456, #2637)
   - using ImGui::Shortcut(ImGuiMod_Ctrl | ImGuiKey_C); with default policy:
     - checks that CTRL+C is pressed,
@@ -84,7 +88,6 @@ Other changes:
 - Inputs: (OSX) Ctrl+Left Click alias as a Right click. (#2343) [@haldean, @ocornut]
 - Inputs: Fixed ImGui::GetKeyName(ImGuiKey_None) from returning "N/A" or "None" depending
   on value of IMGUI_DISABLE_OBSOLETE_KEYIO. It always returns "None".
-- Windows: BeginChild(): fixed visibility of fully clipped child windows and tables to Test Engine.
 - Nav: fixed holding Ctrl or gamepad L1 from not slowing down keyboard/gamepad tweak speed.
   Broken during a refactor refactor for 1.89. Holding Shift/R1 to speed up wasn't broken.
 - Tables: fixed cell background of fully clipped row overlapping with header. (#7575, #7041) [@prabuinet]

imgui.cpp

@@ -5844,10 +5844,18 @@ static ImVec2 CalcWindowAutoFitSize(ImGuiWindow* window, const ImVec2& size_cont
         ImVec2 size_max = ((window->Flags & ImGuiWindowFlags_ChildWindow) && !(window->Flags & ImGuiWindowFlags_Popup)) ? ImVec2(FLT_MAX, FLT_MAX) : ImGui::GetMainViewport()->WorkSize - style.DisplaySafeAreaPadding * 2.0f;
         ImVec2 size_auto_fit = ImClamp(size_desired, size_min, size_max);
 
+        // FIXME: CalcWindowAutoFitSize() doesn't take into account that only one axis may be auto-fit when calculating scrollbars,
+        // we may need to compute/store three variants of size_auto_fit, for x/y/xy.
+        // Here we implement a workaround for child windows only, but a full solution would apply to normal windows as well:
+        if ((window->ChildFlags & ImGuiChildFlags_ResizeX) && !(window->ChildFlags & ImGuiChildFlags_ResizeY))
+            size_auto_fit.y = window->SizeFull.y;
+        else if (!(window->ChildFlags & ImGuiChildFlags_ResizeX) && (window->ChildFlags & ImGuiChildFlags_ResizeY))
+            size_auto_fit.x = window->SizeFull.x;
+
         // When the window cannot fit all contents (either because of constraints, either because screen is too small),
         // we are growing the size on the other axis to compensate for expected scrollbar. FIXME: Might turn bigger than ViewportSize-WindowPadding.
         ImVec2 size_auto_fit_after_constraint = CalcWindowSizeAfterConstraint(window, size_auto_fit);
-        bool will_have_scrollbar_x = (size_auto_fit_after_constraint.x - size_pad.x - decoration_w_without_scrollbars < size_contents.x  && !(window->Flags & ImGuiWindowFlags_NoScrollbar) && (window->Flags & ImGuiWindowFlags_HorizontalScrollbar)) || (window->Flags & ImGuiWindowFlags_AlwaysHorizontalScrollbar);
+        bool will_have_scrollbar_x = (size_auto_fit_after_constraint.x - size_pad.x - decoration_w_without_scrollbars < size_contents.x && !(window->Flags & ImGuiWindowFlags_NoScrollbar) && (window->Flags & ImGuiWindowFlags_HorizontalScrollbar)) || (window->Flags & ImGuiWindowFlags_AlwaysHorizontalScrollbar);
         bool will_have_scrollbar_y = (size_auto_fit_after_constraint.y - size_pad.y - decoration_h_without_scrollbars < size_contents.y && !(window->Flags & ImGuiWindowFlags_NoScrollbar)) || (window->Flags & ImGuiWindowFlags_AlwaysVerticalScrollbar);
         if (will_have_scrollbar_x)
             size_auto_fit.y += style.ScrollbarSize;
@@ -6049,6 +6057,7 @@ static int ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& si
         if (held && g.IO.MouseDoubleClicked[0])
         {
             // Double-clicking bottom or right border auto-fit on this axis
+            // FIXME: CalcWindowAutoFitSize() doesn't take into account that only one side may be auto-fit when calculating scrollbars.
             // FIXME: Support top and right borders: rework CalcResizePosSizeFromAnyCorner() to be reusable in both cases.
             if (border_n == 1 || border_n == 3) // Right and bottom border
             {

imgui.h

@@ -28,7 +28,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.90.7 WIP"
-#define IMGUI_VERSION_NUM   19066
+#define IMGUI_VERSION_NUM   19067
 #define IMGUI_HAS_TABLE
 
 /*