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crystal-imgui

Crystal bindings to Dear ImGui, through cimgui

Introduction

This library lets you use Dear ImGui with the Crystal programming language.

Dear ImGui is an immediate-mode library for programming and rendering graphical user interfaces. But note that just by itself it won't directly let you do those things, it needs to be wired up to code that actually handles rendering and input. You can write these yourself or use a library ("backend"):

Documentation

API documentation is currently missing any actual descriptions, but it cross-links to the well-commented imgui.h header file.

For guidance specific to Crystal and crystal-imgui, see Usage.

Examples of most possible usages of the library are covered in the extensive src/demo.cr (entry point examples/demo_sfml.cr; note that it requires crystal-imgui-sfml).

There's also a small self-contained example from crystal-imgui-sfml.

Installation

Following the installation process of crystal-imgui-sfml is recommended instead (it even provides libcimgui.so automatically), but continue here if you want an alternate route.

Repeat: do not follow these instructions if you're using crystal-imgui-sfml (which in the current state of things you probably are).

crystal-imgui actually binds to the cimgui library. The supported version is bundled as a submodule (for other versions you can try your luck by re-generating sources). This repository needs to have been cloned with submodules:

git clone --recursive https://github.com/oprypin/crystal-imgui

Then you can build cimgui:

cd cimgui
cmake -DCMAKE_CXX_FLAGS='-DIMGUI_USE_WCHAR32' .
cmake --build .
ln -s cimgui.so libcimgui.so  # or .dylib on macOS

Yes, the flag is required (just makes the library play much nicely with Unicode and Crystal), and the symlink is also required, because the library ends up as cimgui.so but somehow is referred by both that name and libcimgui.so.

Building a project

Try the example from inside the folder of crystal-imgui:

crystal run examples/test.cr

Prior to that you'll need to add cimgui to the library search path:

export LD_LIBRARY_PATH="$(pwd)/cimgui"
export LIBRARY_PATH="$(pwd)/cimgui"

For your own project, crystal-imgui will be in a subdirectory, so adjust this accordingly.

Usage

Using crystal-imgui is agnostic of the backend for the most part, you invoke those just at the beginning of a frame, to process inputs, and at the end, to do the actual rendering (generally imgui just builds up the things to be drawn until the end).

The API surface follows Dear ImGui itself very closely. Main differences are:

Contributing

Note that most source files of crystal-imgui are auto-generated from outputs of cimgui.

If you're editing files, make sure they wouldn't be overwritten by generate.cr - in that case that is the file that you should be editing instead. In general, to generate the source code, run this:

crystal generate.cr  # assumes cimgui/ is populated, writes to src/
crystal tool format src

The process to update the ImGui demo is fairly manual. First, run the update tool:

crystal tools/update.cr

The update tool does two things:

Beyond this point, the additional translation must be done manually. As always, please ensure to use the Crystal format tool to format the demo code, otherwise it will fail the build.

Credits

crystal-imgui was made by Oleh Prypin. It uses and is based on Dear ImGui and cimgui.

crystal-imgui is licensed under the terms and conditions of the MIT license.