Windows: latch FontRefSize at time of Begin(), consistent with e.g. TitleBarHeight, and to avoid calling CalcFontSize() on non-current window.

imgui.cpp

@@ -4276,6 +4276,7 @@ ImGuiWindow::ImGuiWindow(ImGuiContext* ctx, const char* name) : DrawListInst(NUL
     SetWindowPosVal = SetWindowPosPivot = ImVec2(FLT_MAX, FLT_MAX);
     LastFrameActive = -1;
     LastTimeActive = -1.0f;
+    FontRefSize = 0.0f;
     FontWindowScale = FontWindowScaleParents = 1.0f;
     SettingsOffset = -1;
     DrawList = &DrawListInst;
@@ -7201,6 +7202,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         window->DC.MenuBarOffset.y = g.NextWindowData.MenuBarOffsetMinVal.y;
         window->TitleBarHeight = (flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : g.FontSize + g.Style.FramePadding.y * 2.0f;
         window->MenuBarHeight = (flags & ImGuiWindowFlags_MenuBar) ? window->DC.MenuBarOffset.y + g.FontSize + g.Style.FramePadding.y * 2.0f : 0.0f;
+        window->FontRefSize = g.FontSize; // Lock this to discourage calling window->CalcFontSize() outside of current window.
 
         // Depending on condition we use previous or current window size to compare against contents size to decide if a scrollbar should be visible.
         // Those flags will be altered further down in the function depending on more conditions.
@@ -9649,7 +9651,7 @@ void ImGui::UpdateMouseWheel()
             {
                 LockWheelingWindow(window, wheel.x);
                 float max_step = window->InnerRect.GetWidth() * 0.67f;
-                float scroll_step = ImTrunc(ImMin(2 * window->CalcFontSize(), max_step));
+                float scroll_step = ImTrunc(ImMin(2 * window->FontRefSize, max_step));
                 SetScrollX(window, window->Scroll.x - wheel.x * scroll_step);
                 g.WheelingWindowScrolledFrame = g.FrameCount;
             }
@@ -9657,7 +9659,7 @@ void ImGui::UpdateMouseWheel()
             {
                 LockWheelingWindow(window, wheel.y);
                 float max_step = window->InnerRect.GetHeight() * 0.67f;
-                float scroll_step = ImTrunc(ImMin(5 * window->CalcFontSize(), max_step));
+                float scroll_step = ImTrunc(ImMin(5 * window->FontRefSize, max_step));
                 SetScrollY(window, window->Scroll.y - wheel.y * scroll_step);
                 g.WheelingWindowScrolledFrame = g.FrameCount;
             }
@@ -12987,7 +12989,7 @@ static void ImGui::NavUpdate()
     {
         // *Fallback* manual-scroll with Nav directional keys when window has no navigable item
         ImGuiWindow* window = g.NavWindow;
-        const float scroll_speed = IM_ROUND(window->CalcFontSize() * 100 * io.DeltaTime); // We need round the scrolling speed because sub-pixel scroll isn't reliably supported.
+        const float scroll_speed = IM_ROUND(window->FontRefSize * 100 * io.DeltaTime); // We need round the scrolling speed because sub-pixel scroll isn't reliably supported.
         const ImGuiDir move_dir = g.NavMoveDir;
         if (window->DC.NavLayersActiveMask == 0x00 && window->DC.NavWindowHasScrollY && move_dir != ImGuiDir_None)
         {
@@ -13177,8 +13179,8 @@ void ImGui::NavUpdateCreateMoveRequest()
         if ((clamp_x || clamp_y) && !inner_rect_rel.Contains(window->NavRectRel[g.NavLayer]))
         {
             IMGUI_DEBUG_LOG_NAV("[nav] NavMoveRequest: clamp NavRectRel for gamepad move\n");
-            float pad_x = ImMin(inner_rect_rel.GetWidth(), window->CalcFontSize() * 0.5f);
-            float pad_y = ImMin(inner_rect_rel.GetHeight(), window->CalcFontSize() * 0.5f); // Terrible approximation for the intent of starting navigation from first fully visible item
+            float pad_x = ImMin(inner_rect_rel.GetWidth(), window->FontRefSize * 0.5f);
+            float pad_y = ImMin(inner_rect_rel.GetHeight(), window->FontRefSize * 0.5f); // Terrible approximation for the intent of starting navigation from first fully visible item
             inner_rect_rel.Min.x = clamp_x ? (inner_rect_rel.Min.x + pad_x) : -FLT_MAX;
             inner_rect_rel.Max.x = clamp_x ? (inner_rect_rel.Max.x - pad_x) : +FLT_MAX;
             inner_rect_rel.Min.y = clamp_y ? (inner_rect_rel.Min.y + pad_y) : -FLT_MAX;
@@ -13436,7 +13438,7 @@ static float ImGui::NavUpdatePageUpPageDown()
     else
     {
         ImRect& nav_rect_rel = window->NavRectRel[g.NavLayer];
-        const float page_offset_y = ImMax(0.0f, window->InnerRect.GetHeight() - window->CalcFontSize() * 1.0f + nav_rect_rel.GetHeight());
+        const float page_offset_y = ImMax(0.0f, window->InnerRect.GetHeight() - window->FontRefSize * 1.0f + nav_rect_rel.GetHeight());
         float nav_scoring_rect_offset_y = 0.0f;
         if (IsKeyPressed(ImGuiKey_PageUp, true))
         {

imgui_internal.h

@@ -2552,6 +2552,7 @@ struct IMGUI_API ImGuiWindow
     ImVector<ImGuiOldColumns> ColumnsStorage;
     float                   FontWindowScale;                    // User scale multiplier per-window, via SetWindowFontScale()
     float                   FontWindowScaleParents;
+    float                   FontRefSize;                        // This is a copy of window->CalcFontSize() at the time of Begin(), trying to phase out CalcFontSize() especially as it may be called on non-current window.
     int                     SettingsOffset;                     // Offset into SettingsWindows[] (offsets 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)