flake: import package.nix from nixpkgs

So we can have more control of the build process compared to overriding
the picom derivation.

Also add expressions to cross-compile picom for arm32, arm64, and x86.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

flake.nix

@@ -7,41 +7,22 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
-  outputs = {
-    self,
-    flake-utils,
-    nixpkgs,
-    git-ignore-nix,
-    ...
-  }:
-    flake-utils.lib.eachDefaultSystem (system: let
+  outputs =
+    { self
+    , flake-utils
+    , nixpkgs
+    , git-ignore-nix
+    , ...
+    }:
+    flake-utils.lib.eachDefaultSystem (system:
+    let
       # like lib.lists.remove, but takes a list of elements to remove
       removeFromList = toRemove: list: pkgs.lib.foldl (l: e: pkgs.lib.remove e l) list toRemove;
-      overlay = self: super: {
-        picom = super.picom.overrideAttrs (oldAttrs: rec {
-          version = "11";
-          pname = "picom";
-          nativeBuildInputs = (removeFromList [ self.asciidoc ] oldAttrs.nativeBuildInputs) ++
-            [
-              self.asciidoctor
-            ];
-          buildInputs =
-            [
-              self.pcre2
-              self.xorg.xcbutil
-              self.libepoxy
-            ] ++ (removeFromList [
-              self.xorg.libXinerama
-              self.xorg.libXext
-              self.pcre
-            ]  oldAttrs.buildInputs);
-          src = git-ignore-nix.lib.gitignoreSource ./.;
-        });
-      };
-      python = pkgs.python3.withPackages (ps: with ps; [
-        xcffib pip dbus-next
-      ]);
-
+      picomOverlay = final: prev: { picom = prev.callPackage ./package.nix { }; };
+      overlays = [
+        (final: prev: { inherit git-ignore-nix; })
+        picomOverlay
+      ];
       pkgs = import nixpkgs {
         inherit system overlays;
         config.allowBroken = true;
@@ -60,15 +41,8 @@
         ];
       };
 
-      overlays = [overlay];
       mkDevShell = p: p.overrideAttrs (o: {
-        nativeBuildInputs = o.nativeBuildInputs ++ (with pkgs; [
-          clang-tools_18
-          llvmPackages_18.clang-unwrapped.python
-          llvmPackages_18.libllvm
-          python
-        ]);
-        hardeningDisable = ["fortify"];
+        hardeningDisable = [ "fortify" ];
         shellHook = ''
           # Workaround a NixOS limitation on sanitizers:
           # See: https://github.com/NixOS/nixpkgs/issues/287763
@@ -77,21 +51,32 @@
           export ASAN_OPTIONS="disable_coredump=0:unmap_shadow_on_exit=1:abort_on_error=1"
         '';
       });
-    in rec {
-      inherit
-        overlay
-        overlays
-        ;
+    in
+    rec {
+      overlay = picomOverlay;
       packages = {
+        picom = pkgs.picom;
         default = pkgs.picom;
-      };
-      devShells.default = mkDevShell packages.default;
+      } // (nixpkgs.lib.optionalAttrs (system == "x86_64-linux") rec {
+        picom-cross = {
+          armv7l = pkgs.pkgsCross.armv7l-hf-multiplatform.picom;
+          aarch64 = pkgs.pkgsCross.aarch64-multiplatform.picom;
+          i686 = pkgs.pkgsi686Linux.picom;
+          merged = pkgs.runCommand "picom-merged" {} ''
+            mkdir $out
+            ln -s ${picom-cross.armv7l} $out/armv7l
+            ln -s ${picom-cross.aarch64} $out/aarch64
+            ln -s ${picom-cross.i686} $out/i686
+          '';
+        };
+      });
+      devShells.default = mkDevShell (packages.default.override { devShell = true; });
       devShells.useClang = devShells.default.override {
         inherit (pkgs.llvmPackages_18) stdenv;
       };
       # build picom and all dependencies with frame pointer, making profiling/debugging easier.
       # WARNING! many many rebuilds
-      devShells.useClangProfile = (mkDevShell profilePkgs.picom).override {
+      devShells.useClangProfile = (mkDevShell (profilePkgs.picom.override { devShell = true; })).override {
         stdenv = profilePkgs.withCFlags "-fno-omit-frame-pointer" profilePkgs.llvmPackages_18.stdenv;
       };
     });

package.nix

@@ -0,0 +1,109 @@
+{ asciidoctor
+, dbus
+, docbook_xml_dtd_45
+, docbook_xsl
+, fetchFromGitHub
+, clang-tools_18
+, llvmPackages_18
+, lib
+, libconfig
+, libdrm
+, libev
+, libGL
+, libepoxy
+, libX11
+, libxcb
+, libxdg_basedir
+, libXext
+, libxml2
+, libxslt
+, makeWrapper
+, meson
+, ninja
+, pcre2
+, pixman
+, pkg-config
+, python3
+, stdenv
+, uthash
+, xcbutil
+, xcbutilimage
+, xcbutilrenderutil
+, xorgproto
+, xwininfo
+, withDebug ? false
+, git-ignore-nix
+, devShell ? false
+}:
+
+let
+  versionFromMeson = s: builtins.head (builtins.match "project\\('picom',.*version: *'([0-9.]*)'.*" s);
+in
+stdenv.mkDerivation (finalAttrs: {
+  pname = "picom";
+  version = versionFromMeson (builtins.readFile ./meson.build);
+
+  src = git-ignore-nix.lib.gitignoreSource ./.;
+
+  strictDeps = true;
+
+
+  nativeBuildInputs = [
+    asciidoctor
+    docbook_xml_dtd_45
+    docbook_xsl
+    makeWrapper
+    meson
+    ninja
+    pkg-config
+  ] ++ (lib.optional devShell [
+    clang-tools_18
+    llvmPackages_18.clang-unwrapped.python
+    llvmPackages_18.libllvm
+    (python3.withPackages (ps: with ps; [
+      xcffib pip dbus-next
+    ]))
+  ]);
+
+  buildInputs = [
+    dbus
+    libconfig
+    libdrm
+    libev
+    libGL
+    libepoxy
+    libX11
+    libxcb
+    libxdg_basedir
+    libXext
+    libxml2
+    libxslt
+    pcre2
+    pixman
+    uthash
+    xcbutil
+    xcbutilimage
+    xcbutilrenderutil
+    xorgproto
+  ];
+
+  # Use "debugoptimized" instead of "debug" so perhaps picom works better in
+  # normal usage too, not just temporary debugging.
+  mesonBuildType = if withDebug then "debugoptimized" else "release";
+  dontStrip = withDebug;
+
+  mesonFlags = [
+    "-Dwith_docs=true"
+  ];
+
+  installFlags = [ "PREFIX=$(out)" ];
+
+  # In debug mode, also copy src directory to store. If you then run `gdb picom`
+  # in the bin directory of picom store path, gdb finds the source files.
+  postInstall = ''
+    wrapProgram $out/bin/picom-trans \
+      --prefix PATH : ${lib.makeBinPath [ xwininfo ]}
+  '' + lib.optionalString withDebug ''
+    cp -r ../src $out/
+  '';
+})