Demo & Debug Windows

Built-in demonstration and debugging windows for Dear ImGui

Dear ImGui provides several built-in windows for demonstration, debugging, and learning. These are invaluable tools for both learning the library and diagnosing issues in your application.

ShowDemoWindow

Displays the comprehensive Dear ImGui demo window showcasing all features.

void ShowDemoWindow(bool* p_open = NULL);

Parameters

p_open · bool* · default: "NULL"

Optional pointer to a boolean controlling window visibility. When the user clicks the close button, this is set to false.

Description

The demo window is the best way to learn Dear ImGui. It demonstrates:

• All widget types and their variants
• Layout and grouping techniques
• Window management features
• Input handling examples
• Tables, trees, and list boxes
• Drag & drop functionality
• Multi-selection patterns
• Custom drawing with ImDrawList
• Performance optimization tips

Example

// Simple usage - always show
ImGui::ShowDemoWindow();

// With close button
bool show_demo = true;
while (running) {
    ImGui::NewFrame();
    
    if (show_demo) {
        ImGui::ShowDemoWindow(&show_demo);
    }
    
    ImGui::Render();
}

With Menu Integration

bool show_demo = false;

if (ImGui::BeginMainMenuBar()) {
    if (ImGui::BeginMenu("Windows")) {
        ImGui::MenuItem("Demo Window", NULL, &show_demo);
        ImGui::EndMenu();
    }
    ImGui::EndMainMenuBar();
}

if (show_demo) {
    ImGui::ShowDemoWindow(&show_demo);
}

The demo window source code (imgui_demo.cpp) is extensively commented and serves as a learning resource. Read through it to understand best practices.

ShowMetricsWindow

Displays the metrics/debugger window showing Dear ImGui internals.

void ShowMetricsWindow(bool* p_open = NULL);

Parameters

p_open · bool* · default: "NULL"

Optional pointer to a boolean controlling window visibility.

Description

The metrics window provides deep insight into Dear ImGui’s internal state:

• Active windows and their properties
• Draw command statistics
• Vertex and index buffer usage
• Memory allocations
• Active ID and hover information
• Font atlas details
• Input state monitoring
• Settings inspection

Example

bool show_metrics = false;

// Toggle with keyboard shortcut
if (ImGui::IsKeyPressed(ImGuiKey_F1)) {
    show_metrics = !show_metrics;
}

if (show_metrics) {
    ImGui::ShowMetricsWindow(&show_metrics);
}

Debugging Window Issues

// When debugging window behavior
ImGui::Begin("My Window");
ImGui::Text("Some content");
ImGui::End();

// Show metrics to inspect window state
ImGui::ShowMetricsWindow();
// Navigate to Windows -> "My Window" to see:
// - Position, Size
// - Flags
// - Draw commands
// - Active/Focused state

Use the metrics window to diagnose performance issues. It shows draw call counts and vertex/index buffer sizes, helping identify rendering bottlenecks.

ShowDebugLogWindow

Displays a simplified log of important Dear ImGui events.

void ShowDebugLogWindow(bool* p_open = NULL);

Parameters

p_open · bool* · default: "NULL"

Optional pointer to a boolean controlling window visibility.

Description

The debug log window records:

• Navigation events
• Focus changes
• Input capture events
• Window creation/destruction
• Table operations
• Multi-select operations
• Other significant state changes

Example

bool show_log = false;

if (ImGui::BeginMainMenuBar()) {
    if (ImGui::BeginMenu("Debug")) {
        ImGui::MenuItem("Debug Log", NULL, &show_log);
        ImGui::EndMenu();
    }
    ImGui::EndMainMenuBar();
}

if (show_log) {
    ImGui::ShowDebugLogWindow(&show_log);
}

Debugging Input Issues

// Enable log when debugging input handling
static bool show_log = true;
ImGui::ShowDebugLogWindow(&show_log);

// Your UI code
if (ImGui::Button("Test Button")) {
    // Check debug log to see:
    // - Whether button received focus
    // - Navigation events
    // - Input routing
}

The debug log is particularly useful when debugging keyboard navigation and focus issues.

ShowAboutWindow

Displays the About window with version, credits, and build information.

void ShowAboutWindow(bool* p_open = NULL);

Parameters

p_open · bool* · default: "NULL"

Optional pointer to a boolean controlling window visibility.

Description

The About window displays:

• Dear ImGui version (e.g., “1.92.7 WIP”)
• Credits and contributors
• Build/system information
• Compiler details
• Configuration flags
• Links to documentation and resources

Example

bool show_about = false;

if (ImGui::BeginMainMenuBar()) {
    if (ImGui::BeginMenu("Help")) {
        if (ImGui::MenuItem("About Dear ImGui")) {
            show_about = true;
        }
        ImGui::EndMenu();
    }
    ImGui::EndMainMenuBar();
}

if (show_about) {
    ImGui::ShowAboutWindow(&show_about);
}

Version Information

// Get version programmatically
const char* version = ImGui::GetVersion();
printf("Using Dear ImGui %s\n", version);

// Show in about window
ImGui::ShowAboutWindow();

Complete Debug UI Example

struct DebugWindows {
    bool show_demo = false;
    bool show_metrics = false;
    bool show_log = false;
    bool show_about = false;
};

static DebugWindows debug;

void RenderDebugMenu() {
    if (ImGui::BeginMainMenuBar()) {
        if (ImGui::BeginMenu("Windows")) {
            ImGui::MenuItem("Demo Window", "F1", &debug.show_demo);
            ImGui::Separator();
            ImGui::MenuItem("Metrics/Debugger", "F2", &debug.show_metrics);
            ImGui::MenuItem("Debug Log", "F3", &debug.show_log);
            ImGui::Separator();
            ImGui::MenuItem("About Dear ImGui", NULL, &debug.show_about);
            ImGui::EndMenu();
        }
        ImGui::EndMainMenuBar();
    }
    
    // Keyboard shortcuts
    if (ImGui::IsKeyPressed(ImGuiKey_F1)) debug.show_demo = !debug.show_demo;
    if (ImGui::IsKeyPressed(ImGuiKey_F2)) debug.show_metrics = !debug.show_metrics;
    if (ImGui::IsKeyPressed(ImGuiKey_F3)) debug.show_log = !debug.show_log;
    
    // Render windows
    if (debug.show_demo) ImGui::ShowDemoWindow(&debug.show_demo);
    if (debug.show_metrics) ImGui::ShowMetricsWindow(&debug.show_metrics);
    if (debug.show_log) ImGui::ShowDebugLogWindow(&debug.show_log);
    if (debug.show_about) ImGui::ShowAboutWindow(&debug.show_about);
}

Keep debug windows disabled in release builds to avoid exposing internal state to end users. Use preprocessor directives:

#ifdef _DEBUG
    ImGui::ShowMetricsWindow();
#endif

Best Practices

Learning the Library

// Always make the demo available during development
#ifdef _DEBUG
    static bool show_demo = true;
    ImGui::ShowDemoWindow(&show_demo);
#endif

Performance Monitoring

// Monitor draw calls and vertex counts
static bool show_metrics = false;
if (ImGui::IsKeyPressed(ImGuiKey_F11)) {
    show_metrics = !show_metrics;
}

if (show_metrics) {
    ImGui::ShowMetricsWindow(&show_metrics);
    // Check "Drawlists" section for performance stats
}

Issue Reporting

// When reporting bugs, include metrics window info
ImGui::ShowMetricsWindow();
// Take a screenshot showing:
// - Window hierarchy
// - Draw command counts
// - Active/Hovered items
// Include in your bug report