Fixed old SetWindowFontScale() api value from not being inherited by child window. Added comments about the right way to scale your UI (load a font at the right side, rebuild atlas, scale style).

+ Added missing IMGUI_API marker to the EmptyString storage used by ImGuiTextBuffer. (#2672)

docs/CHANGELOG.txt

@@ -51,6 +51,8 @@ Other Changes:
   Also still case if ImGuiWindowFlags_NoScrollWithMouse is set (not new), but previously the forwarding
   would be disabled if ImGuiWindowFlags_NoScrollbar was set on the child window, which is not the case
   any more. Forwarding can still be disabled by setting ImGuiWindowFlags_NoInputs. (amend #1502, #1380).
+- Window: Fixed old SetWindowFontScale() api value from not being inherited by child window. Added
+  comments about the right way to scale your UI (load a font at the right side, rebuild atlas, scale style).
 - Scrollbar: Avoid overlapping the opposite side when window (often a child window) is forcibly too small.
 - Combo: Hide arrow when there's not enough space even for the square button.
 - TabBar: Fixed unfocused tab bar separator color (was using ImGuiCol_Tab, should use ImGuiCol_TabUnfocusedActive).
@@ -58,7 +60,7 @@ Other Changes:
   of this, auto-fitting exactly unwrapped text would make it wrap. (fixes initial 1.15 commit, 78645a7d).
 - Scrolling: Added SetScrollHereX(), SetScrollFromPosX() for completeness. (#1580) [@kevreco]
 - Style: Attenuated default opacity of ImGuiCol_Separator in Classic and Light styles.
-- Style: Added style.ColorButtonButton (left/right, defaults to ImGuiDir_Right) to move the color button
+- Style: Added style.ColorButtonPosition (left/right, defaults to ImGuiDir_Right) to move the color button
   of ColorEdit3/ColorEdit4 functions to either side of the inputs.
 - Misc: Added IMGUI_DISABLE_METRICS_WINDOW imconfig.h setting to explicitly compile out ShowMetricsWindow().
 - Debug, Metrics: Added "Tools->Item Picker" tool which allow clicking on a widget to break in the debugger

imgui.h

@@ -280,7 +280,7 @@ namespace ImGui
     IMGUI_API void          SetWindowSize(const ImVec2& size, ImGuiCond cond = 0);                      // (not recommended) set current window size - call within Begin()/End(). set to ImVec2(0,0) to force an auto-fit. prefer using SetNextWindowSize(), as this may incur tearing and minor side-effects.
     IMGUI_API void          SetWindowCollapsed(bool collapsed, ImGuiCond cond = 0);                     // (not recommended) set current window collapsed state. prefer using SetNextWindowCollapsed().
     IMGUI_API void          SetWindowFocus();                                                           // (not recommended) set current window to be focused / top-most. prefer using SetNextWindowFocus().
-    IMGUI_API void          SetWindowFontScale(float scale);                                            // set font scale. Adjust IO.FontGlobalScale if you want to scale all windows
+    IMGUI_API void          SetWindowFontScale(float scale);                                            // set font scale. Adjust IO.FontGlobalScale if you want to scale all windows. This is an old API! For correct scaling, prefer to reload font + rebuild ImFontAtlas + call style.ScaleAllSizes().
     IMGUI_API void          SetWindowPos(const char* name, const ImVec2& pos, ImGuiCond cond = 0);      // set named window position.
     IMGUI_API void          SetWindowSize(const char* name, const ImVec2& size, ImGuiCond cond = 0);    // set named window size. set axis to 0.0f to force an auto-fit on this axis.
     IMGUI_API void          SetWindowCollapsed(const char* name, bool collapsed, ImGuiCond cond = 0);   // set named window collapsed state
@@ -1612,7 +1612,7 @@ struct ImGuiTextFilter
 struct ImGuiTextBuffer
 {
     ImVector<char>      Buf;
-    static char         EmptyString[1];
+    IMGUI_API static char EmptyString[1];
 
     ImGuiTextBuffer()   { }
     inline char         operator[](int i)       { IM_ASSERT(Buf.Data != NULL); return Buf.Data[i]; }

imgui_demo.cpp

@@ -3295,8 +3295,9 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
                 ImGui::TreePop();
             }
 
+            HelpMarker("Those are old settings provided for convenience.\nHowever, the _correct_ way of scaling your UI is currently to reload your font at the designed size, rebuild the font atlas, and call style.ScaleAllSizes() on a reference ImGuiStyle structure.");
             static float window_scale = 1.0f;
-            if (ImGui::DragFloat("this window scale", &window_scale, 0.005f, 0.3f, 2.0f, "%.2f"))   // scale only this window
+            if (ImGui::DragFloat("window scale", &window_scale, 0.005f, 0.3f, 2.0f, "%.2f"))   // scale only this window
                 ImGui::SetWindowFontScale(window_scale);
             ImGui::DragFloat("global scale", &io.FontGlobalScale, 0.005f, 0.3f, 2.0f, "%.2f");      // scale everything
             ImGui::PopItemWidth();

imgui_internal.h

@@ -1317,7 +1317,7 @@ struct IMGUI_API ImGuiWindow
     ImGuiMenuColumns        MenuColumns;                        // Simplified columns storage for menu items
     ImGuiStorage            StateStorage;
     ImVector<ImGuiColumns>  ColumnsStorage;
-    float                   FontWindowScale;                    // User scale multiplier per-window
+    float                   FontWindowScale;                    // User scale multiplier per-window, via SetWindowFontScale()
     int                     SettingsIdx;                        // Index into SettingsWindow[] (indices are always valid as we only grow the array from the back)
 
     ImDrawList*             DrawList;                           // == &DrawListInst (for backward compatibility reason with code using imgui_internal.h we keep this a pointer)
@@ -1344,12 +1344,12 @@ public:
     ImGuiID     GetIDFromRectangle(const ImRect& r_abs);
 
     // We don't use g.FontSize because the window may be != g.CurrentWidow.
-    ImRect      Rect() const                            { return ImRect(Pos.x, Pos.y, Pos.x+Size.x, Pos.y+Size.y); }
-    float       CalcFontSize() const                    { return GImGui->FontBaseSize * FontWindowScale; }
-    float       TitleBarHeight() const                  { return (Flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : CalcFontSize() + GImGui->Style.FramePadding.y * 2.0f; }
-    ImRect      TitleBarRect() const                    { return ImRect(Pos, ImVec2(Pos.x + SizeFull.x, Pos.y + TitleBarHeight())); }
-    float       MenuBarHeight() const                   { return (Flags & ImGuiWindowFlags_MenuBar) ? DC.MenuBarOffset.y + CalcFontSize() + GImGui->Style.FramePadding.y * 2.0f : 0.0f; }
-    ImRect      MenuBarRect() const                     { float y1 = Pos.y + TitleBarHeight(); return ImRect(Pos.x, y1, Pos.x + SizeFull.x, y1 + MenuBarHeight()); }
+    ImRect      Rect() const                { return ImRect(Pos.x, Pos.y, Pos.x+Size.x, Pos.y+Size.y); }
+    float       CalcFontSize() const        { ImGuiContext& g = *GImGui; float scale = g.FontBaseSize * FontWindowScale; if (ParentWindow) scale *= ParentWindow->FontWindowScale; return scale; }
+    float       TitleBarHeight() const      { ImGuiContext& g = *GImGui; return (Flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : CalcFontSize() + g.Style.FramePadding.y * 2.0f; }
+    ImRect      TitleBarRect() const        { return ImRect(Pos, ImVec2(Pos.x + SizeFull.x, Pos.y + TitleBarHeight())); }
+    float       MenuBarHeight() const       { ImGuiContext& g = *GImGui; return (Flags & ImGuiWindowFlags_MenuBar) ? DC.MenuBarOffset.y + CalcFontSize() + g.Style.FramePadding.y * 2.0f : 0.0f; }
+    ImRect      MenuBarRect() const         { float y1 = Pos.y + TitleBarHeight(); return ImRect(Pos.x, y1, Pos.x + SizeFull.x, y1 + MenuBarHeight()); }
 };
 
 // Backup and restore just enough data to be able to use IsItemHovered() on item A after another B in the same window has overwritten the data.