JUCE-imgui

imgui platform backend for JUCE
This needs to be used along with the OpenGL 3 Renderer (imgui_impl_opengl3) as JUCE uses OpenGL
https://github.com/ocornut/imgui
https://github.com/juce-framework/JUCE
https://github.com/ocornut/imgui/wiki/Bindings#frameworkengine-backends

Usage

Download and add imgui_impl_juce.h, imgui_impl_juce.cpp, imgui_impl_juce_config.h to your projects source code
This needs to be used along with the OpenGL 3 Renderer (imgui_impl_opengl3) as Juce supports OpenGL
E.g. ImGui_ImplOpenGL3_Init(juce::OpenGLHelpers::getGLSLVersionString().toUTF8()) Integrate in a project using imgui and JUCE
See the provided example
Follow steps: "Required JUCE v7 openGL rendering scale fix"
Follow steps: "Required Juce ImGui MouseCursor Extensions"

Required JUCE v7 openGL rendering scale fix

Please read the following if this is required for your JUCE project:
Juce_openGL_RenderingScale_Fix/README_Juce_openGL_renderingScale_fix.md

Required Juce ImGui MouseCursor Extensions

Please read the following if this is required for your JUCE project:
Juce_ImGuiMouseCursor_Extensions/README_Juce_ImGuiMouseCursor_Extensions.md
Otherwise disable in imgui_impl_juce_config.h
#define Juce_ImGuiMouseCursor_Extensions 0

Implemented Features

• Platform: Mouse support. Can discriminate Mouse/TouchScreen/Pen.
• Platform: Mouse cursor shape and visibility. Disable with 'io.ConfigFlags |= ImGuiConfigFlags_NoMouseCursorChange'.
• Platform: Juce Mouse cursor extensions. See imgui_impl_juce_config.h
• Platform: Override Mouse wheel scroll sensitivity.
• Platform: Keyboard support.
• Platform: Clipboard support.
• Platform: Multiple ImGuiContexts support. Use case: multiple plugin instances within a DAW.
  (Implementations must follow thread_local guidance in imconfig.h / imgui_impl_juce_config.h)

Unsupported Features

• Gamepad input.
• Certain key presses: Details see ImGui_ImplJuce_KeyPress_ToImGuiKey().

Notable existing juce backend implementations

https://github.com/Krasjet/imgui_juce

Differences:

1. Lock-free implementation
2. No patch required to edit the imconfig.h source
   -> imgui now provides user config.h functionality for thread_local imguiContexts
   -> this is now handled within source/imgui_impl_juce_config.h
3. Fixes MacOS alert sound playing when keys are pressed
4. Fixes MacOS missing text input support for:
   -> command key support
   -> cut (Command+X)
   -> copy (Command+C)
   -> paste (Command+V)
   -> undo (Command+Z)
   -> redo (Shift+Command+Z)
   -> move the insertion point to the beginning of the document (Command+UpArrow)
   -> move the insertion point to the end of the document (Command+DownArrow)
   -> move the insertion point to the beginning of the current line (Command+LeftArrow)
   -> move the insertion point to the end of the current line (Command+RightArrow)
   -> select all (Command+A)
   -> select the text between the insertion point and the beginning of the document (Shift+Command+UpArrow)
   -> select the text between the insertion point and the end of the document (Shift+Command+DownArrow)
   -> select the text between the insertion point and the beginning of the current line (Shift+Command+LeftArrow)
   -> select the text between the insertion point and the end of the current line (Shift+Command+RightArrow)
   -> delete line (Command+delete/backspace)
   -> Additional command functionality and any user functionality using the command key
5. Fixes clipboard functions on MacOS
   -> Which required command key support for copy and paste to and from clipboard
6. Extra mouse wheel scroll sensitivity
   -> Allow user to speed up or slow down the mouse wheel scroll
7. Supports Juce MouseCursor Extensions

Testing

• imgui master branch https://github.com/ocornut/imgui
• imgui docking branch https://github.com/ocornut/imgui/tree/docking
• JUCE version 7.0.9
• Platform: MacOS Silicon (Arm64 architecture)
• Platform: Windows 10 (x86_64 architecture)

Why use this JUCE imgui platform backend over existing dedicated platform backends e.g. osx/win32?

MacOS

• JUCE renders openGL on it's own background render thread (not the main thread)
  • The imgui_impl_osx.mm file has NS (appkit) function calls which are only safe to execute on the main thread
  • From testing this can lead to crashes, bugs and other undefined behaviour
  • Related imgui issues with Mac and the main thread can be found here:
    • "Can only use ImGui OSX backend from main thread #6527"
    • ocornut/imgui#6527
    • https://github.com/ocornut/imgui/compare/master...marzent:imgui:osx-threading-issue#diff-75678f5ba3b98ce72c6b9051d86e452a653fccb131cce2ed305dda38daaee24f
  • The proposed fix is to use dispatch_sync() to ensure NS calls execute on the main thread...
  • BUT this can deadlock with JUCE's message thread
• When an audio plugin is destructed (e.g. plugin deleted from DAW track)...we call ImGui::DestroyContext()
  • When the plugin destruction is completed, JUCE informs the NS system to update (run) which calls onApplicationBecomeInactive():
  • Where the call to ImGui::GetIO() can fail and crash since the context has already been destroyed

Platforms in general

• JUCE handles platform responsibilities like mouse/keyboard input
• So leveraging this allows for one single cross-platform backend rather than multiple platform backends
• Therefore do NOT use this with other platform backends (e.g. win32, osx)