Improve libsdl package (#394)

* Improve libsdl package

* libsdl: Fix possible link order error with use_sdlmain

* libsdl: Fix on_load override

* libsdl: improve on_fetch adding SDL2main (now that on_load works)

* libsdl: Add pic support, improve find_package and remove manual semver check

* Fix a mistake

packages/l/libsdl/xmake.lua

@@ -23,9 +23,74 @@ package("libsdl")
     elseif is_plat("windows", "mingw") then
         add_syslinks("gdi32", "user32", "winmm", "shell32")
     end
-    add_links("SDL2main", "SDL2")
     add_includedirs("include", "include/SDL2")
 
+    add_configs("use_sdlmain", {description = "Use SDL_main entry", default = true, type = "boolean"})
+
+    on_load(function (package)
+        if package:config("use_sdlmain") then
+            package:add("links", "SDL2main", "SDL2")
+        else
+            package:add("links", "SDL2")
+            package:add("defines", "SDL_MAIN_HANDLED")
+        end
+
+        if package:is_plat("macosx") and package:version():ge("2.0.14") then
+            package:add("frameworks", "CoreHaptics", "GameController")
+        end
+    end)
+
+    on_fetch("linux", "macosx", function (package, opt)
+        if opt.system then
+            -- use sdl2-config
+            local sdl2conf = try {function() return os.iorunv("sdl2-config", {"--version", "--cflags", "--libs"}) end}
+            if sdl2conf then
+                sdl2conf = os.argv(sdl2conf)
+                local sdl2ver = table.remove(sdl2conf, 1)
+
+                local result = {}
+                result.version = sdl2ver
+
+                for _, flag in ipairs(sdl2conf) do
+                    if flag:startswith("-L") and #flag > 2 then
+                        -- get linkdirs
+                        local linkdir = flag:sub(3)
+                        if linkdir and os.isdir(linkdir) then
+                            result.linkdirs = result.linkdirs or {}
+                            table.insert(result.linkdirs, linkdir)
+                        end
+                    elseif flag:startswith("-I") and #flag > 2 then
+                        -- get includedirs
+                        local includedir = flag:sub(3)
+                        if includedir and os.isdir(includedir) then
+                            result.includedirs = result.includedirs or {}
+                            table.insert(result.includedirs, includedir)
+                        end
+                    elseif flag:startswith("-l") and #flag > 2 then
+                        -- get links
+                        local link = flag:sub(3)
+                        result.links = result.links or {}
+                        table.insert(result.links, link)
+                    elseif flag:startswith("-D") and #flag > 2 then
+                        -- get defines
+                        local define = flag:sub(3)
+                        result.defines = result.defines or {}
+                        table.insert(result.defines, define)
+                    end
+                end
+
+                return result
+            end
+
+            -- finding using sdl2-config didn't work, fallback on pkgconfig
+            if package.find_package then
+                return package:find_package("pkgconfig::sdl2", opt)
+            else
+                return find_package("pkgconfig::sdl2", opt)
+            end
+        end
+    end)
+
     on_install("windows", "mingw", function (package)
         local arch = package:arch()
         if package:is_plat("mingw") then
@@ -43,13 +108,10 @@ package("libsdl")
         else
             table.insert(configs, "--enable-shared=no")
         end
-        import("package.tools.autoconf").install(package, configs)
-    end)
-
-    on_load(function (package)
-        if package:is_plat("macosx") and package:version():ge("2.0.14") then
-            package:add("frameworks", "CoreHaptics", "GameController")
+        if package:is_plat("linux") and package:config("pic") ~= false then
+            table.insert(configs, "--with-pic")
         end
+        import("package.tools.autoconf").install(package, configs)
     end)
 
     on_test(function (package)