Context: Removed allocator parameters from CreateContext(), they are now setup with SetMemoryAllocators() and shared by all contexts. (#1565, #586, #992, #1007, #1558)

imgui.cpp

@@ -213,6 +213,7 @@
  Here is a change-log of API breaking changes, if you are using one of the functions listed, expect to have to fix some code.
  Also read releases logs https://github.com/ocornut/imgui/releases for more details.
 
+ - 2018/01/20 (1.XX) - removed allocator parameters from CreateContext(), they are now setup with SetMemoryAllocators() and shared by all contexts.
  - 2018/01/11 (1.54) - obsoleted IsAnyWindowHovered() in favor of IsWindowHovered(ImGuiHoveredFlags_AnyWindow). Kept redirection function (will obsolete).
  - 2018/01/11 (1.54) - obsoleted IsAnyWindowFocused() in favor of IsWindowFocused(ImGuiFocusedFlags_AnyWindow). Kept redirection function (will obsolete).
  - 2018/01/03 (1.54) - renamed ImGuiSizeConstraintCallback to ImGuiSizeCallback, ImGuiSizeConstraintCallbackData to ImGuiSizeCallbackData.
@@ -709,6 +710,17 @@ static ImGuiContext     GImDefaultContext;
 ImGuiContext*           GImGui = &GImDefaultContext;
 #endif
 
+// Memory Allocator Functions. Use SetMemoryAllocators() to change them.
+// If you use DLL hotreloading you might need to call SetMemoryAllocators() after reloading code from this file. 
+// Otherwise, you probably don't want to modify them mid-program, and if you use global/static e.g. ImVector<> instances you may need to keep them accessible during program destruction.
+static void*   MallocWrapper(size_t size, void* user_data)    { (void)user_data; return malloc(size); }
+static void    FreeWrapper(void* ptr, void* user_data)        { (void)user_data; free(ptr); }
+
+static void*  (*GImAllocatorAllocFunc)(size_t size, void* user_data) = MallocWrapper;
+static void   (*GImAllocatorFreeFunc)(void* ptr, void* user_data) = FreeWrapper;
+static void*    GImAllocatorUserData = NULL;
+static size_t   GImAllocatorActiveCount = 0;
+
 //-----------------------------------------------------------------------------
 // User facing structures
 //-----------------------------------------------------------------------------
@@ -807,8 +819,6 @@ ImGuiIO::ImGuiIO()
                                 
     // Settings (User Functions)
     RenderDrawListsFn = NULL;
-    MemAllocFn = malloc;
-    MemFreeFn = free;
     GetClipboardTextFn = GetClipboardTextFn_DefaultImpl;   // Platform dependent default implementations
     SetClipboardTextFn = SetClipboardTextFn_DefaultImpl;
     ClipboardUserData = NULL;
@@ -2173,14 +2183,14 @@ float ImGui::CalcWrapWidthForPos(const ImVec2& pos, float wrap_pos_x)
 
 void* ImGui::MemAlloc(size_t sz)
 {
-    GImGui->IO.MetricsAllocs++;
+    GImAllocatorActiveCount++;
-    return GImGui->IO.MemAllocFn(sz);
+    return GImAllocatorAllocFunc(sz, GImAllocatorUserData);
 }
 
 void ImGui::MemFree(void* ptr)
 {
-    if (ptr) GImGui->IO.MetricsAllocs--;
+    if (ptr) GImAllocatorActiveCount--;
-    return GImGui->IO.MemFreeFn(ptr);
+    return GImAllocatorFreeFunc(ptr, GImAllocatorUserData);
 }
 
 const char* ImGui::GetClipboardText()
@@ -2215,23 +2225,24 @@ void ImGui::SetCurrentContext(ImGuiContext* ctx)
 #endif
 }
 
-ImGuiContext* ImGui::CreateContext(void* (*malloc_fn)(size_t), void (*free_fn)(void*))
+void ImGui::SetMemoryAllocators(void* (*alloc_fn)(size_t sz, void* user_data), void(*free_fn)(void* ptr, void* user_data), void* user_data)
 {
-    if (!malloc_fn) malloc_fn = malloc;
+    GImAllocatorAllocFunc = alloc_fn;
-    ImGuiContext* ctx = (ImGuiContext*)malloc_fn(sizeof(ImGuiContext));
+    GImAllocatorFreeFunc = free_fn;
-    IM_PLACEMENT_NEW(ctx) ImGuiContext();
+    GImAllocatorUserData = user_data;
-    ctx->IO.MemAllocFn = malloc_fn;
+}
-    ctx->IO.MemFreeFn = free_fn ? free_fn : free;
+
+ImGuiContext* ImGui::CreateContext()
+{
+    ImGuiContext* ctx = IM_NEW(ImGuiContext)();
     return ctx;
 }
 
 void ImGui::DestroyContext(ImGuiContext* ctx)
 {
-    void (*free_fn)(void*) = ctx->IO.MemFreeFn;
-    ctx->~ImGuiContext();
-    free_fn(ctx);
     if (GImGui == ctx)
         SetCurrentContext(NULL);
+    IM_DELETE(ctx);
 }
 
 ImGuiIO& ImGui::GetIO()
@@ -11668,7 +11679,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
         ImGui::Text("Dear ImGui %s", ImGui::GetVersion());
         ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
         ImGui::Text("%d vertices, %d indices (%d triangles)", ImGui::GetIO().MetricsRenderVertices, ImGui::GetIO().MetricsRenderIndices, ImGui::GetIO().MetricsRenderIndices / 3);
-        ImGui::Text("%d allocations", ImGui::GetIO().MetricsAllocs);
+        ImGui::Text("%d allocations", GImAllocatorActiveCount);
         static bool show_clip_rects = true;
         ImGui::Checkbox("Show clipping rectangles when hovering an ImDrawCmd", &show_clip_rects);
         ImGui::Separator();

imgui.h

@@ -509,10 +509,12 @@ namespace ImGui
     IMGUI_API const char*   GetClipboardText();
     IMGUI_API void          SetClipboardText(const char* text);
 
-    // Internal context access - if you want to use multiple context, share context between modules (e.g. DLL). There is a default context created and active by default.
+    // Context creation and access, if you want to use multiple context, share context between modules (e.g. DLL). There is a default context created and active by default.
     // All contexts share a same ImFontAtlas by default. If you want different font atlas, you can new() them and overwrite the GetIO().Fonts variable of an ImGui context.
+    // All those functions are not reliant on the current context.
     IMGUI_API const char*   GetVersion();
-    IMGUI_API ImGuiContext* CreateContext(void* (*malloc_fn)(size_t) = NULL, void (*free_fn)(void*) = NULL);
+    IMGUI_API void          SetMemoryAllocators(void* (*alloc_fn)(size_t sz, void* user_data), void(*free_fn)(void* ptr, void* user_data), void* user_data = NULL);
+    IMGUI_API ImGuiContext* CreateContext();
     IMGUI_API void          DestroyContext(ImGuiContext* ctx);
     IMGUI_API ImGuiContext* GetCurrentContext();
     IMGUI_API void          SetCurrentContext(ImGuiContext* ctx);
@@ -914,11 +916,6 @@ struct ImGuiIO
     void        (*SetClipboardTextFn)(void* user_data, const char* text);
     void*       ClipboardUserData;
 
-    // Optional: override memory allocations. MemFreeFn() may be called with a NULL pointer.
-    // (default to posix malloc/free)
-    void*       (*MemAllocFn)(size_t sz);
-    void        (*MemFreeFn)(void* ptr);
-
     // Optional: notify OS Input Method Editor of the screen position of your cursor for text input position (e.g. when using Japanese/Chinese IME in Windows)
     // (default to use native imm32 api on Windows)
     void        (*ImeSetInputScreenPosFn)(int x, int y);
@@ -954,7 +951,6 @@ struct ImGuiIO
     bool        WantTextInput;              // Mobile/console: when io.WantTextInput is true, you may display an on-screen keyboard. This is set by ImGui when it wants textual keyboard input to happen (e.g. when a InputText widget is active).
     bool        WantMoveMouse;              // [BETA-NAV] MousePos has been altered, back-end should reposition mouse on next frame. Set only when 'NavMovesMouse=true'.
     float       Framerate;                  // Application framerate estimation, in frame per second. Solely for convenience. Rolling average estimation based on IO.DeltaTime over 120 frames
-    int         MetricsAllocs;              // Number of active memory allocations
     int         MetricsRenderVertices;      // Vertices output during last call to Render()
     int         MetricsRenderIndices;       // Indices output during last call to Render() = number of triangles * 3
     int         MetricsActiveWindows;       // Number of visible root windows (exclude child windows)