crystal-imgui
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"):
- crystal-imgui-sfml - backend using SFML (assumed through CrSFML).
Please refer to its instructions primarily, as it takes over large parts of the installation.
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:
- Functions are lowercased:
ImGui::InputFloat3()
becomesImGui.input_float3
. - Types are all in the module as well:
ImGuiIO
becomesImGui::ImGuiIO
.- But you're welcome to "unpack" those as an opt-in, by running
include ImGui::TopLevel
.
- But you're welcome to "unpack" those as an opt-in, by running
- Enums are namespaced.
- Important: To faithfully preserve the APIs of ImGui where its functions accept pointers that are used both for input and output (and for lack of an obvious alternative), crystal-imgui also requires pointers to be passed to it in the same way.
- However, since Crystal requires very prohibitive circumstances to be able to take an actual pointer, crystal-imgui actually wraps these functions into macros, for which
pointerof(foo.bar)
is just a fake syntax that will be transformed into a call tofoo.bar
for reading and a call tofoo.bar=(value)
for writing. As another example,pointerof(arr[0])
also works - rewritten asarr[0] = value
. - If the input kind expects N values, then a
Slice
of N values should be passed directly instead. - For editable strings, one should pass an
ImGui::TextBuffer
instead.
- However, since Crystal requires very prohibitive circumstances to be able to take an actual pointer, crystal-imgui actually wraps these functions into macros, for which
- String buffers (particularly begin+end pairs) are abstracted as
Slice
orImGui::TextBuffer
.- For the latter, crystal-imgui even takes the liberty to implement the buffer resize callback for unbounded text inputs.
ImVector
is discouraged. Usually you can just work withArray
orSlice
.ImColor
is even more discouraged, in favor ofImVec4
. See some color helper functions in src/imgui.cr.
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:
- Uses
generate_demo.cr
to perform the initial translation from the ImGui demo to Crystal code - Merges changes into
src/demo.cr
so that existing work is not lost
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.
crystal-imgui
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MIT License
Sun, 22 Dec 2024 09:58:26 GMT