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These functions form the backbone of the Dear ImGui render loop. Call them in sequence each frame to process input, build your UI, and generate draw commands for rendering.

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Frame Lifecycle

The typical Dear ImGui frame consists of:
  1. NewFrame() - Start a new frame, process input
  2. UI Code - Build your user interface
  3. Render() - Finalize draw data
  4. GetDrawData() - Retrieve draw commands
  5. Backend Rendering - Submit to graphics API
while (running) {
    ImGui::NewFrame();
    
    // Your UI code here
    ImGui::Begin("My Window");
    ImGui::Text("Hello, world!");
    ImGui::End();
    
    ImGui::Render();
    ImGui_ImplXXX_RenderDrawData(ImGui::GetDrawData());
}

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NewFrame

Starts a new Dear ImGui frame. Call this at the beginning of each frame before submitting any UI commands. 
void NewFrame();

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Description

This function:
  • Processes input from ImGuiIO (mouse, keyboard, gamepad)
  • Updates internal state and timing
  • Prepares for new UI commands
  • Clears the previous frame’s data

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Example

void GameLoop() {
    while (!glfwWindowShouldClose(window)) {
        // Poll events and update ImGui backends
        glfwPollEvents();
        ImGui_ImplGlfw_NewFrame();
        ImGui_ImplOpenGL3_NewFrame();
        
        // Start Dear ImGui frame
        ImGui::NewFrame();
        
        // Build UI
        ImGui::ShowDemoWindow();
        
        // Render
        ImGui::Render();
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
        glfwSwapBuffers(window);
    }
}
Always call your backend’s NewFrame() functions (e.g., ImGui_ImplGlfw_NewFrame()) before calling ImGui::NewFrame().

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EndFrame

Ends the Dear ImGui frame. Automatically called by Render(), but can be called manually if you want to skip rendering. 
void EndFrame();

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Description

This function:
  • Finalizes the current frame’s state
  • Updates window positions and sizes
  • Handles end-of-frame operations
If you call EndFrame() without rendering, you’ll waste CPU cycles. It’s better to not create any windows and skip NewFrame() entirely if you don’t need to render.

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Example

// Skip rendering when window is minimized
if (isMinimized) {
    ImGui::NewFrame();
    ImGui::EndFrame();
    // Don't call Render() or GetDrawData()
} else {
    ImGui::NewFrame();
    // ... UI code ...
    ImGui::Render();
    ImGui_ImplXXX_RenderDrawData(ImGui::GetDrawData());
}

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Render

Ends the Dear ImGui frame and finalizes draw data. Call this after submitting all UI commands. 
void Render();

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Description

This function:
  • Calls EndFrame() internally
  • Finalizes all draw lists
  • Prepares ImDrawData for rendering
  • Sorts draw commands by texture and layer

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Example

ImGui::NewFrame();

// Build your UI
ImGui::Begin("Control Panel");
ImGui::Button("Click Me");
ImGui::End();

ImGui::Begin("Debug Info");
ImGui::Text("FPS: %.1f", ImGui::GetIO().Framerate);
ImGui::End();

// Finalize frame
ImGui::Render();

// Now you can retrieve draw data
ImDrawData* draw_data = ImGui::GetDrawData();
You must call Render() before calling GetDrawData(). The draw data is only valid after finalization.

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GetDrawData

Retrieves the draw data generated by the current frame. Pass this to your rendering backend. 
ImDrawData* GetDrawData();

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Returns

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return
ImDrawData*
Pointer to the draw data structure containing all draw commands for the frame. Returns NULL if Render() hasn’t been called yet.

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Description

The returned ImDrawData contains:
  • All draw commands organized by command lists
  • Vertex and index buffers
  • Texture bindings
  • Clipping rectangles
  • Display position and size

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Example

// After calling Render()
ImDrawData* draw_data = ImGui::GetDrawData();

if (draw_data != nullptr) {
    // Pass to your rendering backend
    ImGui_ImplOpenGL3_RenderDrawData(draw_data);
    // or
    ImGui_ImplDX11_RenderDrawData(draw_data);
    // or
    ImGui_ImplVulkan_RenderDrawData(draw_data);
}

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Validation

ImDrawData* draw_data = ImGui::GetDrawData();

if (draw_data && draw_data->Valid) {
    printf("Total draw commands: %d\n", draw_data->TotalVtxCount);
    printf("Display size: %.0fx%.0f\n", 
           draw_data->DisplaySize.x, 
           draw_data->DisplaySize.y);
    
    for (int n = 0; n < draw_data->CmdListsCount; n++) {
        const ImDrawList* cmd_list = draw_data->CmdLists[n];
        printf("Command list %d: %d vertices, %d indices\n",
               n, cmd_list->VtxBuffer.Size, cmd_list->IdxBuffer.Size);
    }
}
The draw data is only valid until the next call to NewFrame(). Don’t cache this pointer across frames.

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Complete Example

#include "imgui.h"
#include "imgui_impl_glfw.h"
#include "imgui_impl_opengl3.h"
#include <GLFW/glfw3.h>

int main() {
    // Initialize GLFW and OpenGL
    glfwInit();
    GLFWwindow* window = glfwCreateWindow(1280, 720, "ImGui Example", NULL, NULL);
    glfwMakeContextCurrent(window);
    glfwSwapInterval(1);
    
    // Setup Dear ImGui context
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO();
    
    // Setup backends
    ImGui_ImplGlfw_InitForOpenGL(window, true);
    ImGui_ImplOpenGL3_Init("#version 130");
    
    // Main loop
    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();
        
        // Start ImGui frame
        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplGlfw_NewFrame();
        ImGui::NewFrame();
        
        // Build UI
        ImGui::Begin("Hello, ImGui!");
        ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 
                    1000.0f / io.Framerate, io.Framerate);
        ImGui::End();
        
        // Render
        ImGui::Render();
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
        glClearColor(0.45f, 0.55f, 0.60f, 1.00f);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
        
        glfwSwapBuffers(window);
    }
    
    // Cleanup
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplGlfw_Shutdown();
    ImGui::DestroyContext();
    glfwDestroyWindow(window);
    glfwTerminate();
    
    return 0;
}

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