Crash on play button, after compilation

Unreal ImGui

Unreal ImGui is an Unreal Engine 4 plug-in that integrates Dear ImGui developed by Omar Cornut.

Dear ImGui is an immediate-mode graphical user interface library that is very lightweight and easy to use. It can be very useful when creating debugging tools.

Status

Version: 1.22

ImGui version: 1.74

Supported engine version: 4.26*

* Plugin has been tested and if necessary updated to compile and work with this engine version. As long as possible I will try to maintain backward compatibility of existing features and possibly but not necessarily when adding new features. When it comes to bare-bone ImGui version it should be at least backward compatible with the engine version 4.15. For NetImgui it needs to be determined.

Current work

Currently, I'm a little busy outside of this project so changes come slowly. But here is what to expect in the reasonably near future:

Stability first, so fixes for more critical issues like an invalidation of handles after reloading texture resources will be pushed first. The same goes for merges.
There are a few smaller issues that I'm aware of and that might be not reported but which I want to fix.
ImGui needs to be updated.
Smaller features might be slowly pushed but bigger ones will need to wait. The same goes for merges.
There is a branch with NetImgui which is really good, and which will be eventually merged to master, but first I want to fix a few issues that I know about (some are discussed in thread #28). In the meantime, the NetImgui branch is pretty much ready to use.

About

The main goal of this plugin is to provide a basic integration of the Dear ImGui which will be easy to use from the game code.

My main focus used to be on debugging and for that this plugin should work out of the box. It is possible to use it for different purposes but depending on the use case it may require some adaptations.

To support multi-PIE, each world gets its own ImGui context to which it can draw. All that is managed by the plugin in a way that should be invisible for the game code. I plan to extend it to allow own contexts and widgets but right now I don't have enough time to commit to that.

As of recently, the plugin has the net_imgui branch with an integration of the NetImgui developed by Sammyfreg. This is still experimental, but it is possible to already download and use it. Many thanks for the library and for the initial integration.

Key features

Multi-PIE support with each world getting its own ImGui context.
Automatic switching between different ImGui contexts.
Delegates for functions with ImGui content.
Support for Unreal textures.

How to Set up

To use this plug-in, you will need a C++ Unreal project.

Installation

Content of this repository needs to be placed in the Plugins directory under the project root: [Project Root]/Plugins/ImGui/. After you compile and run you should notice that ImGui module is now available.

Note that plugins can be also placed in the engine directory [UE4 Root]/Engine/Plugins/ but I didn't try it with this project.

If you want to use NetImgui, instead of please look at the How to Set up NetImgui.

Setting module type

The ImGui module type is set to Developer, what means that if it is not referenced by other runtime modules, it can be automatically excluded from shipping builds. This is convenient when using this plugging for debugging but if you want to change it to other type, you can do it in module description section in ImGui.uplugin file.

Developer type was depreciated in UE 4.24. I keep it for backward compatibility while I can, but if you get a UBT warning about module type, simply change it to DeveloperTool or Runtime.

Setting up module dependencies

To use ImGui in other modules you need to add it as a private or public dependency in their Build.cs files:

PrivateDependencyModuleNames.Add("ImGui");

or

PublicDependencyModuleNames.Add("ImGui");

You might also want to use ImGui only in certain builds:

if (Target.Configuration != UnrealTargetConfiguration.Shipping)
{
	PrivateDependencyModuleNames.Add("ImGui");
}

Conditional compilation

You can conditionally compile ImGui code by checking IMGUI_API:

#ifded IMGUI_API
#include <imgui.h>
#endif

// ... somewhere in your code
#ifded IMGUI_API
// ImGui code
#endif

Above code is fine but it requires wrapping include directives and does not follow the usual pattern used in Unreal. To improve that, you can add the following code to one of your headers (or a precompiled header, if you use one):

// ImGuiCommon.h
#pragma once

#ifdef IMGUI_API
#define WITH_IMGUI 1
#else
#define WITH_IMGUI 0
#endif // IMGUI_API

#if WITH_IMGUI
#include <imgui.h>
#endif // WITH_IMGUI

And then use it like this:

#include "ImGuiCommon.h"

// ... somewhere in your code
#if WITH_IMGUI
// ImGui code
#endif

How to Set up NetImgui

To use NetImgui, use content of the net_imgui branch in place of master. This will be gradually merged into the master but until then you need to use that experimental branch.

Similarly like ImGui, NetImgui is built as part of the UnrealImGui plugin and no other integration steps are required.

To be able to connect to the Unreal editor or application that use NetImgui, you need to run a server (netImguiServer). Please, see the NetImgui page for instructions how to get it.

After launching the server for the first time, you need to add two client configurations, for ports 8889 and 8890. After that, you can either initialise connection from the server or set it to autoconnection mode. More info will be added later.

Once you establish connection, you can use a top bar to switch between contexts and modes. In standalone game it should be one context and in the editor one editor context, plus one for each PIE instance. Please, note that all those features are experimental and might evolve. Any input is welcomed.

How to use it

Using ImGui in code

ImGui can be used from functions registered as ImGui delegates or directly in game code. However, if code is running outside of the game thread or is executed outside of the world update scope, delegates are a better choice.

Delegates have an additional advantage that their content will work also when game is paused.

ImGui Delegates

To use ImGui delegates, include ImGuiDelegates.h.

There are two major types of ImGui delegates: world and multi-context. First are created on demand for every world and are cleared once that world becomes invalid. They are designed to be used primarily by worlds objects. In opposition, multi-context delegates are called for every updated world, so the same code can be called multiple times per frame but in different contexts.

Delegates are called typically during world post actor tick event but they have alternative versions called during world tick start. In engine versions that does not support world post actor tick, that is below 4.18, all delegates are called during world tick start.

Delegates are called in order that allows multi-context delegates to add content before and after world objects:

multi-context early debug
world early debug
world update
world debug
multi-context debug.

FImGuiModule has delegates interface but it is depreciated and will be removed soon. Major issue with that interface is that it needs a module instance, what can be a problem when trying to register static objects. Additional issue is a requirement to always unregister with a handle.

Multi-context

In multi-PIE sessions each world gets its own ImGui context which is selected at the beginning of the world update. All that happens in the background and should allow debug code to stay context agnostic.

If your content is rendered in the wrong context, try using one of the ImGui delegates that should be always called after the right context is already set in ImGui.

Using Unreal textures

Unreal ImGui allows to register textures in order to use them in ImGui. To do that, include ImGuiModule.h and use FImGuiModule interface.

After registration you will get a texture handle, declared in ImGuiTextureHandle.h, that you need to pass to the ImGui API.

// Texture handle defined like this
FImGuiTextureHandle TextureHandle;

// Registration and update
TextureHandle = FImGuiModule::Get().RegisterTexture("TextureName", Texture);

// Release
FImGuiModule::Get().ReleaseTexture(TextureHandle);

// Find by name
TextureHandle = FImGuiModule::Get().FindTextureHandle("TextureName");

// Example of usage (it is implicitly converted to ImTextureID)
ImGui::Image(TextureHandle, Size);

Input mode

Right after the start ImGui will work in render-only mode. To interact with it, you need to activate input mode either by changing Input Enabled property from code, using ImGui.ToggleInput command or with a keyboard shortcut.

Sharing input

It is possible to enable input sharing features to pass keyboard, gamepad or mouse events to the game. Note, that the original design assumed that plugin should consume all input to isolate debug from game. While sharing keyboard or gamepad is pretty straightforward and works by passing input events to the viewport, mouse sharing works in a bit different way. Since the ImGui widget overlays the whole viewport, widget needs to switch hit visibility and update position in the background. It might be possible to generate a custom collision geometry matching ImGui and simplifying working with mouse and touch inputs, but I don't plan to work on this right now.

The default behaviour can be configured in input settings and changed during runtime by modifying Keyboard Input Shared, Gamepad Input Shared and Mouse Input Shared properties or ImGui.ToggleKeyboardInputSharing, ImGui.ToggleGamepadInputSharing and ImGui.ToggleMouseInputSharing commands.

Keyboard and gamepad navigation

When using ImGui on consoles you most probably need to enable keyboard and/or gamepad navigaiton. Both are ImGui features that allow to use it without mouse. See ImGui documentation for more details.

You can toggle those features by changing Keyboard Navigation and Gamepad Navigation properties or using ImGui.ToggleKeyboardNavigationand ImGui.ToggleGamepadNavigation commands.

Navigating around ImGui canvas

Most of the time ImGui canvas will be larger from the viewport. When ImGui is in the input mode, it is possible to change which part of the canvas should be visible on the screen. To do that press and hold Left Shift + Left Alt and use mouse to adjust.

Mouse Wheel - Zoom in or out.
Right Mouse Button - Drag canvas with ImGui content.
Middle Mouse Button - Drag frame representing which part of the canvas will be visible after ending the navigation mode.

The orange rectangle represents a scaled viewport and the area that will be visible on the screen after releasing keys. Zooming will scale that box and dragging with the middle mouse button will move everything.

The black rectangle represents a canvas border. You can drag canvas using the right mouse button. Dragging canvas will add a render offset between ImGui content and the viewport.

Image(s) needed.

Properties

ImGui module has a set of properties that allow to modify its behaviour:

Input Enabled - Whether ImGui should receive input. It is possible to assign a keyboard shortcut to toggle this property.
Keyboard Navigation- Whether ImGui keyboard navigation feature is enabled.
Gamepad Navigation - Whether ImGui gamepad navigation feature is enabled.
Keyboard Input Shared - Whether keyboard input should be shared with the game. Default behaviour can be configured in input settings.
Gamepad Input Shared - Whether gamepad input should be shared with the game. Default behaviour can be configured in input settings.
Mouse Input Shared - Whether mouse input should be shared with the game. Default behaviour can be configured in input settings.
Show Demo - Whether to show ImGui demo.

All properties can be changed by corresponding console commands or from code.

You can get properties interface through the module instance:

FImGuiModule::Get().GetProperties();

Console commands

ImGui.ToggleInput - Toggle ImGui input mode. It is possible to assign a keyboard shortcut to this command.
ImGui.ToggleKeyboardNavigation - Toggle ImGui keyboard navigation.
ImGui.ToggleGamepadNavigation - Toggle ImGui gamepad navigation.
ImGui.ToggleKeyboardInputSharing - Toggle ImGui keyboard input sharing.
ImGui.ToggleGamepadInputSharing - Toggle ImGui gamepad input sharing.
ImGui.ToggleMouseInputSharing - Toggle ImGui mouse input sharing.
ImGui.ToggleDemo - Toggle ImGui demo.

Console debug variables

There is a self-debug functionality build into this plugin. This is hidden by default as it is hardly useful outside of this pluguin. To enable it, go to ImGuiModuleDebug.h and change IMGUI_MODULE_DEVELOPER.

ImGui.Debug.Widget - Show debug for SImGuiWidget.
ImGui.Debug.Input - Show debug for input state.

Settings

Plugin settings can be found in Project Settings/Plugins/ImGui panel. There is a bunch of properties allowing to tweak input handling, keyboard shortcuts (one for now), canvas size and DPI scale.

Extensions

ImGui Input Handler Class - Path to own implementation of ImGui Input Handler that allows limited customization of the input handling. If not set, then the default implementation is used.

If you decide to implement an own handler, please keep in mind that I'm thinking about replacing it.

Input

Share Keyboard Input - Whether by default, ImGui should share with game keyboard input.
Share Gamepad Input - Whether by default, ImGui should share with game gamepad input.
Share Mouse Input - Whether by default, ImGui should share with game mouse input.
Use Software Cursor - Whether ImGui should draw its own cursor in place of the hardware one.

Keyboard shortcuts

Toggle Input - Allows to define a shortcut key to a command that toggles the input mode. Note that this is using DebugExecBindings which is not available in shipping builds.

License

Unreal ImGui is licensed under the MIT License, see LICENSE for more information.

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