backends: add SDL1.2 Compat backend

Added the SDL12-Compat backend, using a shim library which implements the `sdl1.2` API over SDL2.

The new `sdl12-compat` backend should be used for SDL1 applications when:
 * the platform doesn't have `dispmanx` anymore (e.g. `rpi` platforms with RaspiOS Bullseye and later)
 * `sdl2` has a working accelerated video & rendering drivers
 * not running under `x11` (i.e. KMS)

Note: for SDL1+Videocore specific applications, which use directly the dispmanx/legacy GL stack (e.g. `pcsx-rearmed`, `advmame-1.4`, etc.), the backend will not help.

Author: cmitu

scriptmodules/supplementary/backends.sh

@@ -18,6 +18,9 @@ function _list_backends() {
     local id="$1"
     backends=()
 
+    # skip the 'depends' packages
+    [[ ${__mod_info[$id/section]} == "depends" ]] && return 1
+
     local flags="${__mod_info[$id/flags]}"
     local sdl
     if isPlatform "videocore" && hasFlag "$flags" "sdl1-videocore"; then
@@ -35,6 +38,7 @@ function _list_backends() {
     if [[ "$sdl" == "sdl1" ]]; then
         backends["default"]="SDL1 Framebuffer driver"
         isPlatform "dispmanx" && backends["dispmanx"]="SDL1 DispmanX driver"
+        isPlatform "kms" && ! isPlatform "dispmanx" && backends["sdl12-compat"]="SDL1 Compat driver"
     elif [[ "$sdl" == "sdl2" ]]; then
         if isPlatform "videocore"; then
             default="SDL2 videocore driver"
@@ -109,6 +113,9 @@ function gui_configure_backends() {
                     continue
                 fi
             fi
+            if [[ "$choice" == "sdl12-compat" ]] && ! rp_isInstalled "sdl12-compat"; then
+                rp_callModule "sdl12-compat" _auto_
+            fi
             local func="_backend_set_$id"
             if fnExists "$func"; then
                 rp_callModule "$id" _backend_set "$choice" 1

scriptmodules/supplementary/runcommand/runcommand.sh

@@ -1062,6 +1062,9 @@ function config_backend() {
                 fi
                 COMMAND="SDL1_VIDEODRIVER=dispmanx $COMMAND"
                 ;;
+            sdl12-compat)
+                COMMAND="LD_PRELOAD=\"$ROOTDIR/supplementary/sdl12-compat/libSDL-1.2.so.0\" $COMMAND"
+                ;;
             x11)
                 XINIT=1
                 XINIT_WM=1

scriptmodules/supplementary/sdl1.sh

@@ -11,9 +11,9 @@
 
 rp_module_id="sdl1"
 rp_module_desc="SDL 1.2.15 with rpi fixes and dispmanx"
-rp_module_licence="GPL2 https://hg.libsdl.org/SDL/raw-file/7676476631ce/COPYING"
+rp_module_licence="GPL2 https://raw.githubusercontent.com/libsdl-org/SDL-1.2/main/COPYING"
 rp_module_section="depends"
-rp_module_flags="!all rpi"
+rp_module_flags="!all rpi dispmanx"
 
 function get_pkg_ver_sdl1() {
     local basever

scriptmodules/supplementary/sdl12-compat.sh

@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+
+# This file is part of The RetroPie Project
+#
+# The RetroPie Project is the legal property of its developers, whose names are
+# too numerous to list here. Please refer to the COPYRIGHT.md file distributed with this source.
+#
+# See the LICENSE.md file at the top-level directory of this distribution and
+# at https://raw.githubusercontent.com/RetroPie/RetroPie-Setup/master/LICENSE.md
+#
+
+rp_module_id="sdl12-compat"
+rp_module_desc="SDL1.2 compatibility layer that uses SDL2 under the hood"
+rp_module_help="Provides a binary and source compatible API for programs written against SDL 1.2, but it uses SDL 2.0 behind the scenes"
+rp_module_licence="ZLIB https://raw.githubusercontent.com/libsdl-org/sdl12-compat/main/LICENSE.txt"
+rp_module_repo="git https://github.com/libsdl-org/sdl12-compat :_version_sdl12-compat"
+rp_module_section="depends"
+rp_module_flags="!x11"
+
+function _version_sdl12-compat() {
+    local ver="1.2.68"
+    if [[ "$1" == "short" ]]; then
+        echo $ver
+    else
+        echo "release-$ver"
+    fi
+}
+function depend_sdl12-compat() {
+    getDepends libsdl2-dev cmake
+}
+
+function sources_sdl12-compat() {
+    gitPullOrClone
+}
+
+function build_sdl12-compat() {
+    cmake -DSDL12TESTS=OFF -DSDL12DEVEL=OFF .
+    make
+    md_ret_require="$md_build/libSDL-1.2.so.$(_version_sdl12-compat short)"
+}
+
+function install_sdl12-compat() {
+    md_ret_files=(
+        libSDL-1.2.so."$(_version_sdl12-compat short)"
+        README.md
+        LICENSE.txt
+    )
+}
+
+function configure_sdl12-compat() {
+    ldconfig -nN "$md_inst"
+}