ImGui Drawing the cursor

🖱 Drawing the Cursor on Screen Using ImGui

This guide demonstrates how to draw a simple visual overlay (e.g., a green rectangle around your mouse cursor) using Dear ImGui via the ClickableTransparentOverlay library.

We’ll use ImGui.NET, the official .NET binding for ImGui, and render directly to a fullscreen transparent overlay window that doesn't block mouse input.

💡 What is ImGui?

ImGui (Immediate Mode GUI) is a fast, minimal UI library used for debugging, dev tools, overlays, and custom editors. Unlike traditional retained-mode UI libraries, ImGui redraws everything each frame — making it great for real-time tools like HUDs and debug panels.

📦 Requirements

Make sure you have this NuGet package:

#r "nuget: ClickableTransparentOverlay, 10.2.0"

This package provides a base Overlay class that handles window creation, ImGui setup, and rendering.

✅ Complete Example: Cursor Tracker with ImGui

#r "nuget: ClickableTransparentOverlay, 10.2.0"

using ClickableTransparentOverlay;
using System.Threading.Tasks;
using ImGuiNET;

try
{
    Log.Info("Booting up ImGui OSD");

    using var overlay = new SampleOverlay(cancellationToken);
    await overlay.Run(); // Starts the overlay loop
}
catch (Exception ex)
{
    Log.Error("ImGui OSD encountered an error", ex);
    throw;
}
finally
{
    Log.Info("ImGui OSD was closed");
}

internal class SampleOverlay : Overlay
{
    private readonly CancellationToken cancellationToken;

    public SampleOverlay(CancellationToken cancellationToken)
        : base( // Fullscreen on primary monitor
            System.Windows.Forms.Screen.PrimaryScreen.Bounds.Width,
            System.Windows.Forms.Screen.PrimaryScreen.Bounds.Height)
    {
        this.cancellationToken = cancellationToken;
    }

    // Called every frame
    protected override void Render()
    {
        // Graceful shutdown if requested
        if (cancellationToken.IsCancellationRequested)
        {
            Close();
            return;
        }

        // Get the current ImGui draw list
        var drawList = ImGui.GetBackgroundDrawList();

        // Get the current cursor position (in screen coordinates)
        var cursorPosition = UnsafeNative.GetCursorPosition();

        // Draw a green 10x10 rectangle centered on the cursor
        drawList.AddRect(
            cursorPosition.OffsetBy(-5, -5).ToVector2(),
            cursorPosition.OffsetBy(5, 5).ToVector2(),
            ImGui.GetColorU32(new System.Numerics.Vector4(0f, 1f, 0f, 1f)), // Green
            0f,                    // Corner rounding
            ImDrawFlags.None,     // No flags
            1f                    // Thickness
        );
    }
}

📌 Key Concepts:

ImGui.GetBackgroundDrawList() gives you access to a canvas for drawing in the background layer.
AddRect() draws a rectangle in screen coordinates.
The color is passed as a Vector4 (RGBA) and converted via ImGui.GetColorU32.
OffsetBy(x, y) is assumed to be a helper that returns a new Point offset by given delta.
The Overlay base class runs a frame loop for you and handles transparency.

🎯 Want More?

Add a label or tooltip at the cursor
Draw different shapes depending on state
Detect clicks or interaction with the overlay
Show debug data or game-related visuals in real-time