Context Management

Functions for creating and managing Dear ImGui contexts

Context management functions allow you to create, destroy, and switch between multiple Dear ImGui contexts. Each context maintains its own state, including font atlas, style, and window data.

Each context creates its own ImFontAtlas by default. You can share a font atlas between contexts by passing it to CreateContext().

CreateContext

Creates a new Dear ImGui context.

ImGuiContext* CreateContext(ImFontAtlas* shared_font_atlas = NULL);

Parameters

shared_font_atlas · ImFontAtlas* · default: "NULL"

Optional font atlas to share between contexts. If NULL, a new font atlas will be created.

Returns

return · ImGuiContext*

Pointer to the newly created context.

Example

// Create a context with its own font atlas
ImGuiContext* ctx1 = ImGui::CreateContext();

// Create a context that shares the font atlas
ImFontAtlas* shared_atlas = new ImFontAtlas();
ImGuiContext* ctx2 = ImGui::CreateContext(shared_atlas);
ImGuiContext* ctx3 = ImGui::CreateContext(shared_atlas);

For DLL users: heaps and globals are not shared across DLL boundaries. You must call SetCurrentContext() + SetAllocatorFunctions() for each static/DLL boundary.

DestroyContext

Destroys a Dear ImGui context and frees all associated resources.

void DestroyContext(ImGuiContext* ctx = NULL);

Parameters

ctx · ImGuiContext* · default: "NULL"

The context to destroy. If NULL, destroys the current context.

Example

// Destroy a specific context
ImGuiContext* ctx = ImGui::CreateContext();
ImGui::DestroyContext(ctx);

// Destroy the current context
ImGui::DestroyContext();

Always destroy contexts before application shutdown to prevent memory leaks.

GetCurrentContext

Retrieves the currently active Dear ImGui context.

ImGuiContext* GetCurrentContext();

Returns

return · ImGuiContext*

Pointer to the current context, or NULL if no context is set.

Example

ImGuiContext* current = ImGui::GetCurrentContext();
if (current != nullptr) {
    // Context is active
}

SetCurrentContext

Sets the active Dear ImGui context. All subsequent ImGui calls will operate on this context.

void SetCurrentContext(ImGuiContext* ctx);

Parameters

ctx · ImGuiContext* · required

The context to make active.

Example

// Create two contexts for different windows
ImGuiContext* ctx_main = ImGui::CreateContext();
ImGuiContext* ctx_overlay = ImGui::CreateContext();

// Render main window
ImGui::SetCurrentContext(ctx_main);
ImGui::NewFrame();
ImGui::Begin("Main Window");
// ... main window content ...
ImGui::End();
ImGui::Render();

// Render overlay window
ImGui::SetCurrentContext(ctx_overlay);
ImGui::NewFrame();
ImGui::Begin("Overlay");
// ... overlay content ...
ImGui::End();
ImGui::Render();

When switching contexts, make sure to complete the frame (call Render() or EndFrame()) before switching to avoid state corruption.

Multi-Context Usage Pattern

// Initialization
ImFontAtlas* shared_atlas = new ImFontAtlas();
ImGuiContext* ctx1 = ImGui::CreateContext(shared_atlas);
ImGuiContext* ctx2 = ImGui::CreateContext(shared_atlas);

// Per-frame rendering
void RenderFrame() {
    // Render first context
    ImGui::SetCurrentContext(ctx1);
    ImGui::NewFrame();
    ImGui::Begin("Window 1");
    ImGui::Text("First context");
    ImGui::End();
    ImGui::Render();
    ImGui_ImplXXX_RenderDrawData(ImGui::GetDrawData());
    
    // Render second context
    ImGui::SetCurrentContext(ctx2);
    ImGui::NewFrame();
    ImGui::Begin("Window 2");
    ImGui::Text("Second context");
    ImGui::End();
    ImGui::Render();
    ImGui_ImplXXX_RenderDrawData(ImGui::GetDrawData());
}

// Cleanup
ImGui::DestroyContext(ctx1);
ImGui::DestroyContext(ctx2);
delete shared_atlas;