Internals: Added ImChunkStream, used by window settings. (more generic followup to 4c13807, the class will be used more extensively by Tables)

imgui.cpp

@@ -2525,7 +2525,7 @@ ImGuiWindow::ImGuiWindow(ImGuiContext* context, const char* name)
     LastTimeActive = -1.0f;
     ItemWidthDefault = 0.0f;
     FontWindowScale = 1.0f;
-    SettingsIdx = -1;
+    SettingsOffset = -1;
 
     DrawList = &DrawListInst;
     DrawList->_OwnerName = Name;
@@ -3818,7 +3818,6 @@ void ImGui::Shutdown(ImGuiContext* context)
     g.PrivateClipboard.clear();
     g.InputTextState.ClearFreeMemory();
 
-    g.SettingsWindowsNames.clear();
     g.SettingsWindows.clear();
     g.SettingsHandlers.clear();
 
@@ -4704,7 +4703,7 @@ static ImGuiWindow* CreateNewWindow(const char* name, ImVec2 size, ImGuiWindowFl
         if (ImGuiWindowSettings* settings = ImGui::FindWindowSettings(window->ID))
         {
             // Retrieve settings from .ini file
-            window->SettingsIdx = g.SettingsWindows.index_from_ptr(settings);
+            window->SettingsOffset = g.SettingsWindows.offset_from_ptr(settings);
             SetWindowConditionAllowFlags(window, ImGuiCond_FirstUseEver, false);
             window->Pos = ImVec2(settings->Pos.x, settings->Pos.y);
             window->Collapsed = settings->Collapsed;
@@ -9205,27 +9204,31 @@ void ImGui::MarkIniSettingsDirty(ImGuiWindow* window)
 ImGuiWindowSettings* ImGui::CreateNewWindowSettings(const char* name)
 {
     ImGuiContext& g = *GImGui;
-    g.SettingsWindows.push_back(ImGuiWindowSettings());
-    ImGuiWindowSettings* settings = &g.SettingsWindows.back();
+
 #if !IMGUI_DEBUG_INI_SETTINGS
     // Skip to the "###" marker if any. We don't skip past to match the behavior of GetID()
     // Preserve the full string when IMGUI_DEBUG_INI_SETTINGS is set to make .ini inspection easier.
     if (const char* p = strstr(name, "###"))
         name = p;
 #endif
-    size_t name_len = strlen(name);
-    settings->NameOffset = g.SettingsWindowsNames.size();
-    g.SettingsWindowsNames.append(name, name + name_len + 1); // Append with zero terminator
+    const size_t name_len = strlen(name);
+
+    // Allocate chunk
+    const size_t chunk_size = sizeof(ImGuiWindowSettings) + name_len + 1;
+    ImGuiWindowSettings* settings = g.SettingsWindows.alloc_chunk(chunk_size);
+    IM_PLACEMENT_NEW(settings) ImGuiWindowSettings();
     settings->ID = ImHashStr(name, name_len);
+    memcpy(settings->GetName(), name, name_len + 1);   // Store with zero terminator
+
     return settings;
 }
 
 ImGuiWindowSettings* ImGui::FindWindowSettings(ImGuiID id)
 {
     ImGuiContext& g = *GImGui;
-    for (int i = 0; i != g.SettingsWindows.Size; i++)
-        if (g.SettingsWindows[i].ID == id)
-            return &g.SettingsWindows[i];
+    for (ImGuiWindowSettings* settings = g.SettingsWindows.begin(); settings != NULL; settings = g.SettingsWindows.next_chunk(settings))
+        if (settings->ID == id)
+            return settings;
     return NULL;
 }
 
@@ -9380,11 +9383,11 @@ static void WindowSettingsHandler_WriteAll(ImGuiContext* ctx, ImGuiSettingsHandl
         if (window->Flags & ImGuiWindowFlags_NoSavedSettings)
             continue;
 
-        ImGuiWindowSettings* settings = (window->SettingsIdx != -1) ? &g.SettingsWindows[window->SettingsIdx] : ImGui::FindWindowSettings(window->ID);
+        ImGuiWindowSettings* settings = (window->SettingsOffset != -1) ? g.SettingsWindows.ptr_from_offset(window->SettingsOffset) : ImGui::FindWindowSettings(window->ID);
         if (!settings)
         {
             settings = ImGui::CreateNewWindowSettings(window->Name);
-            window->SettingsIdx = g.SettingsWindows.index_from_ptr(settings);
+            window->SettingsOffset = g.SettingsWindows.offset_from_ptr(settings);
         }
         IM_ASSERT(settings->ID == window->ID);
         settings->Pos = ImVec2ih((short)window->Pos.x, (short)window->Pos.y);
@@ -9393,11 +9396,10 @@ static void WindowSettingsHandler_WriteAll(ImGuiContext* ctx, ImGuiSettingsHandl
     }
 
     // Write to text buffer
-    buf->reserve(buf->size() + g.SettingsWindows.Size * 96); // ballpark reserve
-    for (int i = 0; i != g.SettingsWindows.Size; i++)
+    buf->reserve(buf->size() + g.SettingsWindows.size() * 6); // ballpark reserve
+    for (ImGuiWindowSettings* settings = g.SettingsWindows.begin(); settings != NULL; settings = g.SettingsWindows.next_chunk(settings))
     {
-        const ImGuiWindowSettings* settings = &g.SettingsWindows[i];
-        const char* settings_name = g.SettingsWindowsNames.c_str() + settings->NameOffset;
+        const char* settings_name = settings->GetName();
         buf->appendf("[%s][%s]\n", handler->TypeName, settings_name);
         buf->appendf("Pos=%d,%d\n", settings->Pos.x, settings->Pos.y);
         buf->appendf("Size=%d,%d\n", settings->Size.x, settings->Size.y);

imgui_internal.h

@@ -88,7 +88,6 @@ struct ImGuiTabItem;                // Storage for a tab item (within a tab bar)
 struct ImGuiWindow;                 // Storage for one window
 struct ImGuiWindowTempData;         // Temporary storage for one window (that's the data which in theory we could ditch at the end of the frame)
 struct ImGuiWindowSettings;         // Storage for a window .ini settings (we keep one of those even if the actual window wasn't instanced during this session)
-template<typename T> struct ImPool; // Basic keyed storage for contiguous instances, slow/amortized insertion, O(1) indexable, O(Log N) queries by ID
 
 // Use your programming IDE "Go to definition" facility on the names of the center columns to find the actual flags/enum lists.
 typedef int ImGuiLayoutType;            // -> enum ImGuiLayoutType_         // Enum: Horizontal or vertical
@@ -145,6 +144,7 @@ extern IMGUI_API ImGuiContext* GImGui;  // Current implicit context pointer
 // - Helpers: Maths
 // - Helper: ImBoolVector
 // - Helper: ImPool<>
+// - Helper: ImChunkStream<>
 //-----------------------------------------------------------------------------
 
 // Macros
@@ -326,6 +326,28 @@ struct IMGUI_API ImPool
     int         GetSize() const                     { return Buf.Size; }
 };
 
+// Helper: ImChunkStream<>
+// Build and iterate a contiguous stream of variable-sized structures.
+// This is used by Settings to store persistent data while reducing allocation count.
+// We store the chunk size first, and align the final size on 4 bytes boundaries (this what the '(X + 3) & ~3' statement is for)
+// The tedious/zealous amount of casting is to avoid -Wcast-align warnings.
+template<typename T>
+struct IMGUI_API ImChunkStream
+{
+    ImVector<char>  Buf;
+
+    void    clear()                     { Buf.clear(); }
+    bool    empty() const               { return Buf.Size == 0; }
+    int     size() const                { return Buf.Size; }
+    T*      alloc_chunk(size_t sz)      { size_t HDR_SZ = 4; sz = ((HDR_SZ + sz) + 3u) & ~3u; int off = Buf.Size; Buf.resize(off + (int)sz); ((int*)(void*)(Buf.Data + off))[0] = (int)sz; return (T*)(void*)(Buf.Data + off + (int)HDR_SZ); }
+    T*      begin()                     { size_t HDR_SZ = 4; if (!Buf.Data) return NULL; return (T*)(void*)(Buf.Data + HDR_SZ); }
+    T*      next_chunk(T* p)            { size_t HDR_SZ = 4; IM_ASSERT(p >= begin() && p < end()); p = (T*)(void*)((char*)(void*)p + chunk_size(p)); if (p == (T*)(void*)((char*)end() + HDR_SZ)) return (T*)0; IM_ASSERT(p < end()); return p; }
+    int     chunk_size(const T* p)      { return ((const int*)p)[-1]; }
+    T*      end()                       { return (T*)(void*)(Buf.Data + Buf.Size); }
+    int     offset_from_ptr(const T* p) { IM_ASSERT(p >= begin() && p < end()); const ptrdiff_t off = (const char*)p - Buf.Data; return (int)off; }
+    T*      ptr_from_offset(int off)    { IM_ASSERT(off >= 4 && off < Buf.Size); return (T*)(void*)(Buf.Data + off); }
+};
+
 //-----------------------------------------------------------------------------
 // Misc data structures
 //-----------------------------------------------------------------------------
@@ -681,15 +703,16 @@ struct IMGUI_API ImGuiInputTextState
 
 // Windows data saved in imgui.ini file
 // Because we never destroy or rename ImGuiWindowSettings, we can store the names in a separate buffer easily.
+// (this is designed to be stored in a ImChunkStream buffer, with the variable-length Name following our structure)
 struct ImGuiWindowSettings
 {
-    int         NameOffset;     // Offset into SettingsWindowNames[]
     ImGuiID     ID;
     ImVec2ih    Pos;
     ImVec2ih    Size;
     bool        Collapsed;
 
-    ImGuiWindowSettings()       { NameOffset = -1; ID = 0; Pos = Size = ImVec2ih(0, 0); Collapsed = false; }
+    ImGuiWindowSettings()       { ID = 0; Pos = Size = ImVec2ih(0, 0); Collapsed = false; }
+    char* GetName()             { return (char*)(this + 1); }
 };
 
 struct ImGuiSettingsHandler
@@ -1057,8 +1080,7 @@ struct ImGuiContext
     float                   SettingsDirtyTimer;                 // Save .ini Settings to memory when time reaches zero
     ImGuiTextBuffer         SettingsIniData;                    // In memory .ini settings
     ImVector<ImGuiSettingsHandler>      SettingsHandlers;       // List of .ini settings handlers
-    ImVector<ImGuiWindowSettings>  SettingsWindows;             // ImGuiWindow .ini settings entries (parsed from the last loaded .ini file and maintained on saving)
-    ImGuiTextBuffer                SettingsWindowsNames;        // Names for SettingsWindows
+    ImChunkStream<ImGuiWindowSettings>  SettingsWindows;        // ImGuiWindow .ini settings entries
 
     // Logging
     bool                    LogEnabled;
@@ -1369,7 +1391,7 @@ struct IMGUI_API ImGuiWindow
     ImGuiStorage            StateStorage;
     ImVector<ImGuiColumns>  ColumnsStorage;
     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)
+    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)
     ImDrawList              DrawListInst;