Move "ImGui's files" from right in the middle, to a dear-imgui/ git subtree

[folays]

Hello,

In this pull request, I have moved the Dear ImGui's files form "in the middle of all AllenDang's files" to a new completely independent and self-contained dear-imgui/ directory.

(this is a step in addition to the split you already done this year, by splitting this repo from https://github.com/AllenDang/giu)

This new dear-imgui/ directory is a git subtree directory, which means that :

• you can super easily pull latest "Dear ImGui" into your dear-imgui/ subdirectory (git subtree pull)
• you can super easily "extract" local modification to "Dear ImGui" code, if you were to propose changes to (C++) Dear ImGui, and thus super easily create a pull request to "Dear ImGui" code.

Hint : I needed that because, indeed, I have some bug in "Dear ImGui" base code (ocornut/imgui#3795) that:

• occurs in a Go program, which uses https://github.com/AllenDang/giu
• I was willing to identify the bug and fix it in "Dear ImGui" imgui.cpp
• I do not wanted to re-create a sample app in C++
• I wanted to fix https://github.com/AllenDang/giu (or rather fix it's dependency), which meant fixing the imgui.cpp code (official "Dear ImGui") in https://github.com/AllenDang/imgui-go
• I wanted to be able to "push upstream" the modification to imgui.cpp, to Dear ImGui (git subtree push)
  • (which mean "git subptree push" the dear-imgui/ folder to my own ocornut/imgui's fork, and create a pull request from there)

So I forked your github.com/AllenDang/imgui-go repo, and created a folays.imgui-v1.85 branch.
Here are the commands that I did to create it :

grep IMGUI_VERSION imgui.h
-> 1.85

git checkout -b folays.imgui-v1.85 # because you are currently based on v1.85

git subtree add  --prefix=dear-imgui https://github.com/ocornut/imgui.git v1.85 --squash
git subtree pull --prefix=dear-imgui https://github.com/ocornut/imgui.git v1.85 --squash # no-op
-> # From ssh://github.com/ocornut/imgui
   #  * tag                 v1.85      -> FETCH_HEAD
   # Subtree is already at commit 55d35d8387c15bf0cfd71861df67af8cfbda7456.

diff -ru dear-imgui/ ./ | grep -r 'Only in dear-imgui/'
-> (standard input):Only in dear-imgui/: .editorconfig
   (standard input):Only in dear-imgui/: .gitattributes
   (standard input):Only in dear-imgui/: .github
   (standard input):Only in dear-imgui/: backends
   (standard input):Only in dear-imgui/: docs
   (standard input):Only in dear-imgui/: examples

diff -ru dear-imgui/ ./ | grep -- ---
-> --- dear-imgui/.gitignore	2021-12-23 08:30:27.000000000 +0100
   --- dear-imgui/imgui.cpp	2021-12-23 08:30:27.000000000 +0100
   --- dear-imgui/imgui.h	2021-12-23 08:30:27.000000000 +0100
   --- dear-imgui/imgui_internal.h	2021-12-23 08:30:27.000000000 +0100
   --- dear-imgui/imgui_widgets.cpp	2021-12-23 08:30:27.000000000 +0100

diff -ru dear-imgui/ ./ | grep -v ^Only > ../PATCH_imgui-go_diff_to_imgui_v1.85.patch

# remove all ROOT/ files which are already in dear-imgui/
( cd dear-imgui/ && find . -type f -print0 ) | xargs -0 -n1 -- git rm

git checkout HEAD LICENSE.txt .gitignore # restore some stuff

# below : do not "symlink" but rather "#include", because Go Modules (go mod download) IGNORE symlinks.
for name in $(cd dear-imgui/ && ls -1f *.{cpp,h}); do printf '#include "dear-imgui/%s"\n' $name > $name ; done
for name in $(cd dear-imgui/ && ls -1f *.{cpp,h}); do git add $name ; done

# re-add local modifications to dear-imgui/ (modifications exclusives to imgui-go)
patch -d ./dear-imgui/ -p1 < ../PATCH_imgui-go_diff_to_imgui_v1.85.patch

git checkout dear-imgui/.gitignore # restore probably no-more-wanted local modifications
git add dear-imgui/

git commit # ...

I also git add a a new file, /git_pull_dear-imgui.sh which you can use to "pull" new Dear ImGui version from upstream.

Here is what I could do if I wanted to update to Dear ImGui v1.86 (released... yesterday?)

git checkout folays.imgui-v1.85 # fetch this very branch from this pull request

git checkout -b folays.imgui-v1.86
sh ./git_pull_dear-imgui.sh v1.86 # "git subtree pull" from Dear ImGui v1.86
    
go clean -cache
go build ./ # check if it compiles

# Hint 1) It does not compile, there is some SMALL changes in ImGui's (`imgui.h`) ImGuiListClipper struct,
#  (1 struct field removed, 2 or 3 added) which need to be reflected in the wrapper ListClipper.{cpp,h},
#  and while I could update those manually, I feel that you have some sort of procedure to update them automatically?

# Hint 2) For whatever reason, it works even if it SHOULD NOT, if you did not "go clean -cache". Dunno why...

# ... Fix ListClipper.{cpp,h} so that it compiles
    
git commit
git push origin folays.imgui-v1.86
# or git tag whatever tagname you use to be compliant w.r.t. Go Modules.

Also, I think that you are substantially derived from inkyblackness/imgui-go, but I could not figure your thought process.
I'm somewhat curious :

• I guess that you expose an API (the Go API thus exposed) probably adapted to https://github.com/AllenDang/giu needs
• Way more curious : You adopted a different way to generate the pure "C++ to C" wrappers ?
  • Full Swig automation ?
  • Swig was used only as a "working base", and then from now on, you do all updates to those wrappers manually ?

Hope you understand that the purpose of this change is to ease :

• pulling from Dear ImGui upstream (which was not really an hassle)
• more importantly : being able to fork your github.com/AllenDang/imgui-go repo, fix imgui.cpp directly, while being able to still track and pull upstream changes, and independently also being able to "extract" local changes (with "git subtree push") to propose patches (via a pull request) to Dear ImGui (ocornut).

Regards,

[folays]

Another example, after that, you could :

git remote add upstream_imgui https://github.com/ocornut/imgui.git

# don't fetch tags (--no-tags), but yes, fetch them, but in a specifc refspec
# (to not clutter your own repos tags, with the tags of a 3rd party repos)
git fetch --no-tags upstream_imgui '+refs/tags/*:refs/tags_upstream_imgui/*'

$ cat .git/refs/tags_upstream_imgui/v1.85
55d35d8387c15bf0cfd71861df67af8cfbda7456 # <- commit of Dear ImGui v1.85

git diff refs/tags_upstream_imgui/v1.85 folays.imgui-v1.85:dear-imgui/
# OR :
# - git diff refs/tags_upstream_imgui/v1.85 HEAD:dear-imgui/ # if your HEAD is "near" v1.85

Which would display ONLY you local changes to officlal Dear ImGui sources.

In this case, the git diff would reveal :

$ git diff refs/tags_upstream_imgui/v1.85 folays.imgui-v1.85:dear-imgui/ |grep -vE '^(---|\+\+\+) ' | cut -c1 | sort | uniq -c
  48
  55 +
   2 -
   8 @
   4 d
   4 i

Your 55 lines added, 2 removed, on 4 files (8 sections) compared from Dear ImGui sources.

Regards,