gnu: Add imgui.

* gnu/packages/toolkits.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Register it.

gnu/local.mk

@@ -582,6 +582,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/packages/time.scm				\
   %D%/packages/tls.scm				\
   %D%/packages/tmux.scm				\
+  %D%/packages/toolkits.scm			\
   %D%/packages/tor.scm				\
   %D%/packages/tv.scm				\
   %D%/packages/uglifyjs.scm			\

gnu/packages/toolkits.scm

@@ -0,0 +1,104 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2022 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu packages toolkits)
+  #:use-module (gnu packages gl)
+  #:use-module (gnu packages sdl)
+  #:use-module ((guix licenses) #:prefix license:)
+  #:use-module (guix packages)
+  #:use-module (guix utils)
+  #:use-module (guix build-system gnu)
+  #:use-module (guix git-download))
+
+(define-public imgui
+  (package
+    (name "imgui")
+    (version "1.86")
+    (source (origin
+              (method git-fetch)
+              (uri (git-reference
+                    (url "https://github.com/ocornut/imgui")
+                    (commit (string-append "v" version))))
+              (file-name (git-file-name name version))
+              (sha256
+               (base32
+                "02a7b05zrka20jhzag2jb4jl624i1m456bsv69jb9zgys2p9dv1n"))
+              (modules '((guix build utils)))
+              (snippet
+               '(begin
+                  ;; Contains fonts and other unneeded files.
+                  (delete-file-recursively "misc")))))
+    (outputs '("out" "doc"))
+    (build-system gnu-build-system)
+    (arguments
+     `(#:tests? #f                      ;no test suite
+       #:modules ((guix build gnu-build-system)
+                  (guix build utils)
+                  (ice-9 ftw)
+                  (srfi srfi-26))
+       #:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'adjust-includes
+           (lambda _
+             (substitute* (find-files "." "(\\.cpp|\\.mm)$")
+               (("#include <SDL")
+                "#include <SDL2/SDL"))))
+         (delete 'configure)
+         (replace 'build
+           (lambda _
+             ;; Build main library.
+             (invoke ,(cc-for-target) "-I" (getcwd)
+                     "-g" "-O2" "-fPIC" "-shared"
+                     "-lGL" "-lSDL2" "-lglfw"
+                     "-o" "libimgui.so"
+                     "imgui.cpp"
+                     "imgui_draw.cpp"
+                     ;; Include the supported backends.
+                     "backends/imgui_impl_glfw.cpp"
+                     "backends/imgui_impl_sdl.cpp"
+                     "backends/imgui_impl_opengl2.cpp"
+                     "backends/imgui_impl_opengl3.cpp")))
+         (replace 'install
+           (lambda* (#:key outputs #:allow-other-keys)
+             (let* ((out (assoc-ref outputs "out"))
+                    (doc (assoc-ref outputs "doc"))
+                    (header? (cut string-suffix? ".h" <>))
+                    (imgui-headers (scandir "." header?))
+                    (backend-headers (find-files
+                                      "backends"
+                                      "(glfw|opengl|sdl|vulkan).*\\.h$")))
+               (install-file "libimgui.so" (string-append out "/lib"))
+               ;; Install headers.
+               (for-each (lambda (f)
+                           (install-file f (string-append out "/include/imgui")))
+                         imgui-headers)
+               (for-each (lambda (f)
+                           (install-file f (string-append
+                                            out "/include/imgui/backends")))
+                         backend-headers)
+               ;; Install examples.
+               (copy-recursively
+                "examples" (string-append
+                            doc "/share/imgui/examples"))))))))
+    (inputs (list glfw mesa sdl2))
+    (home-page "https://github.com/ocornut/imgui")
+    (synopsis "Graphical user interface library for C++")
+    (description "@code{dear imgui} (also know as ImGui) is a graphical user
+interface library for C++.  It outputs vertex buffers that can be rendered in
+a 3D application.  It is fast, renderer agnostic and self-contained.")
+    (license license:expat)))