Internals: extracted a more reusable BeginViewportSideBar() out of BeginMainMenuBar(). (#3966, #3518)

Complement ca34c81c in docking branch which removed assumption that we can't tell size ahead of Begin().

imgui.cpp

@@ -10566,9 +10566,9 @@ static void ImGui::UpdateViewportsNewFrame()
         ImGuiViewportP* viewport = g.Viewports[n];
 
         // Lock down space taken by menu bars and status bars, reset the offset for fucntions like BeginMainMenuBar() to alter them again.
-        viewport->WorkOffsetMin = viewport->CurrWorkOffsetMin;
-        viewport->WorkOffsetMax = viewport->CurrWorkOffsetMax;
-        viewport->CurrWorkOffsetMin = viewport->CurrWorkOffsetMax = ImVec2(0.0f, 0.0f);
+        viewport->WorkOffsetMin = viewport->BuildWorkOffsetMin;
+        viewport->WorkOffsetMax = viewport->BuildWorkOffsetMax;
+        viewport->BuildWorkOffsetMin = viewport->BuildWorkOffsetMax = ImVec2(0.0f, 0.0f);
         viewport->UpdateWorkRect();
     }
 }

imgui_internal.h

@@ -1180,14 +1180,21 @@ struct ImGuiViewportP : public ImGuiViewport
 
     ImVec2              WorkOffsetMin;          // Work Area: Offset from Pos to top-left corner of Work Area. Generally (0,0) or (0,+main_menu_bar_height). Work Area is Full Area but without menu-bars/status-bars (so WorkArea always fit inside Pos/Size!)
     ImVec2              WorkOffsetMax;          // Work Area: Offset from Pos+Size to bottom-right corner of Work Area. Generally (0,0) or (0,-status_bar_height).
-    ImVec2              CurrWorkOffsetMin;      // Work Area: Offset being built/increased during current frame
-    ImVec2              CurrWorkOffsetMax;      // Work Area: Offset being built/decreased during current frame
+    ImVec2              BuildWorkOffsetMin;     // Work Area: Offset being built during current frame. Generally >= 0.0f.
+    ImVec2              BuildWorkOffsetMax;     // Work Area: Offset being built during current frame. Generally <= 0.0f.
 
     ImGuiViewportP()    { DrawListsLastFrame[0] = DrawListsLastFrame[1] = -1; DrawLists[0] = DrawLists[1] = NULL; }
     ~ImGuiViewportP()   { if (DrawLists[0]) IM_DELETE(DrawLists[0]); if (DrawLists[1]) IM_DELETE(DrawLists[1]); }
+
+    // Calculate work rect pos/size given a set of offset (we have 1 pair of offset for rect locked from last frame data, and 1 pair for currently building rect)
+    ImVec2  CalcWorkRectPos(const ImVec2& off_min) const                            { return ImVec2(Pos.x + off_min.x, Pos.y + off_min.y); }
+    ImVec2  CalcWorkRectSize(const ImVec2& off_min, const ImVec2& off_max) const    { return ImVec2(ImMax(0.0f, Size.x - off_min.x + off_max.x), ImMax(0.0f, Size.y - off_min.y + off_max.y)); }
+    void    UpdateWorkRect()            { WorkPos = CalcWorkRectPos(WorkOffsetMin); WorkSize = CalcWorkRectSize(WorkOffsetMin, WorkOffsetMax); } // Update public fields
+
+    // Helpers to retrieve ImRect (we don't need to store BuildWorkRect as every access tend to change it, hence the code asymmetry)
     ImRect  GetMainRect() const         { return ImRect(Pos.x, Pos.y, Pos.x + Size.x, Pos.y + Size.y); }
     ImRect  GetWorkRect() const         { return ImRect(WorkPos.x, WorkPos.y, WorkPos.x + WorkSize.x, WorkPos.y + WorkSize.y); }
-    void    UpdateWorkRect()        { WorkPos = ImVec2(Pos.x + WorkOffsetMin.x, Pos.y + WorkOffsetMin.y); WorkSize = ImVec2(ImMax(0.0f, Size.x - WorkOffsetMin.x + WorkOffsetMax.x), ImMax(0.0f, Size.y - WorkOffsetMin.y + WorkOffsetMax.y)); }
+    ImRect  GetBuildWorkRect() const    { ImVec2 pos = CalcWorkRectPos(BuildWorkOffsetMin); ImVec2 size = CalcWorkRectSize(BuildWorkOffsetMin, BuildWorkOffsetMax); return ImRect(pos.x, pos.y, pos.x + size.x, pos.y + size.y); }
 };
 
 //-----------------------------------------------------------------------------
@@ -2309,6 +2316,7 @@ namespace ImGui
     IMGUI_API ImGuiWindow*  GetTopMostPopupModal();
     IMGUI_API ImVec2        FindBestWindowPosForPopup(ImGuiWindow* window);
     IMGUI_API ImVec2        FindBestWindowPosForPopupEx(const ImVec2& ref_pos, const ImVec2& size, ImGuiDir* last_dir, const ImRect& r_outer, const ImRect& r_avoid, ImGuiPopupPositionPolicy policy);
+    IMGUI_API bool          BeginViewportSideBar(const char* name, ImGuiViewport* viewport, ImGuiDir dir, float size, ImGuiWindowFlags window_flags);
 
     // Gamepad/Keyboard Navigation
     IMGUI_API void          NavInitWindow(ImGuiWindow* window, bool force_reinit);

imgui_widgets.cpp

@@ -6602,46 +6602,63 @@ void ImGui::EndMenuBar()
     window->DC.MenuBarAppending = false;
 }
 
-bool ImGui::BeginMainMenuBar()
-{
-    ImGuiContext& g = *GImGui;
-    ImGuiViewportP* viewport = (ImGuiViewportP*)(void*)GetMainViewport();
-    ImGuiWindow* menu_bar_window = FindWindowByName("##MainMenuBar");
-
-    // For the main menu bar, which cannot be moved, we honor g.Style.DisplaySafeAreaPadding to ensure text can be visible on a TV set.
-    g.NextWindowData.MenuBarOffsetMinVal = ImVec2(g.Style.DisplaySafeAreaPadding.x, ImMax(g.Style.DisplaySafeAreaPadding.y - g.Style.FramePadding.y, 0.0f));
+// Important: calling order matters!
+// FIXME: Somehow overlapping with docking tech.
+// FIXME: The "rect-cut" aspect of this could be formalized into a lower-level helper (rect-cut: https://halt.software/dead-simple-layouts)
+bool ImGui::BeginViewportSideBar(const char* name, ImGuiViewport* viewport_p, ImGuiDir dir, float axis_size, ImGuiWindowFlags window_flags)
+{
+    IM_ASSERT(dir != ImGuiDir_None);
+
+    ImGuiWindow* bar_window = FindWindowByName(name);
+    if (bar_window == NULL || bar_window->BeginCount == 0)
+    {
+        // Calculate and set window size/position
+        ImGuiViewportP* viewport = (ImGuiViewportP*)(void*)(viewport_p ? viewport_p : GetMainViewport());
+        ImRect avail_rect = viewport->GetBuildWorkRect();
+        ImGuiAxis axis = (dir == ImGuiDir_Up || dir == ImGuiDir_Down) ? ImGuiAxis_Y : ImGuiAxis_X;
+        ImVec2 pos = avail_rect.Min;
+        if (dir == ImGuiDir_Right || dir == ImGuiDir_Down)
+            pos[axis] = avail_rect.Max[axis] - axis_size;
+        ImVec2 size = avail_rect.GetSize();
+        size[axis] = axis_size;
+        SetNextWindowPos(pos);
+        SetNextWindowSize(size);
 
-    // Get our rectangle at the top of the work area
-    if (menu_bar_window == NULL || menu_bar_window->BeginCount == 0)
-    {
-        // Set window position
-        // We don't attempt to calculate our height ahead, as it depends on the per-viewport font size.
-        // However menu-bar will affect the minimum window size so we'll get the right height.
-        ImVec2 menu_bar_pos = viewport->Pos + viewport->CurrWorkOffsetMin;
-        ImVec2 menu_bar_size = ImVec2(viewport->Size.x - viewport->CurrWorkOffsetMin.x + viewport->CurrWorkOffsetMax.x, 1.0f);
-        SetNextWindowPos(menu_bar_pos);
-        SetNextWindowSize(menu_bar_size);
+        // Report our size into work area (for next frame) using actual window size
+        if (dir == ImGuiDir_Up || dir == ImGuiDir_Left)
+            viewport->BuildWorkOffsetMin[axis] += axis_size;
+        else if (dir == ImGuiDir_Down || dir == ImGuiDir_Right)
+            viewport->BuildWorkOffsetMax[axis] -= axis_size;
     }
 
-    // Create window
+    window_flags |= ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove;
     PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
-    PushStyleVar(ImGuiStyleVar_WindowMinSize, ImVec2(0, 0)); // Lift normal size constraint, however the presence of a menu-bar will give us the minimum height we want.
-    ImGuiWindowFlags window_flags = ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_MenuBar;
-    bool is_open = Begin("##MainMenuBar", NULL, window_flags) && BeginMenuBar();
+    PushStyleVar(ImGuiStyleVar_WindowMinSize, ImVec2(0, 0)); // Lift normal size constraint
+    bool is_open = Begin(name, NULL, window_flags);
     PopStyleVar(2);
 
-    // Report our size into work area (for next frame) using actual window size
-    menu_bar_window = GetCurrentWindow();
-    if (menu_bar_window->BeginCount == 1)
-        viewport->CurrWorkOffsetMin.y += menu_bar_window->Size.y;
+    return is_open;
+}
 
+bool ImGui::BeginMainMenuBar()
+{
+    ImGuiContext& g = *GImGui;
+    ImGuiViewportP* viewport = (ImGuiViewportP*)(void*)GetMainViewport();
+
+    // For the main menu bar, which cannot be moved, we honor g.Style.DisplaySafeAreaPadding to ensure text can be visible on a TV set.
+    // FIXME: This could be generalized as an opt-in way to clamp window->DC.CursorStartPos to avoid SafeArea?
+    // FIXME: Consider removing support for safe area down the line... it's messy. Nowadays consoles have support for TV calibration in OS settings.
+    g.NextWindowData.MenuBarOffsetMinVal = ImVec2(g.Style.DisplaySafeAreaPadding.x, ImMax(g.Style.DisplaySafeAreaPadding.y - g.Style.FramePadding.y, 0.0f));
+    ImGuiWindowFlags window_flags = ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_MenuBar;
+    float height = GetFrameHeight();
+    bool is_open = BeginViewportSideBar("##MainMenuBar", viewport, ImGuiDir_Up, height, window_flags);
     g.NextWindowData.MenuBarOffsetMinVal = ImVec2(0.0f, 0.0f);
-    if (!is_open)
-    {
+
+    if (is_open)
+        BeginMenuBar();
+    else
         End();
-        return false;
-    }
-    return true; //-V1020
+    return is_open;
 }
 
 void ImGui::EndMainMenuBar()