Add sdl-renderer flag to protect against older SDL versions that do n…

…ot have SDL_RenderGeometry

dear-imgui.cabal

@@ -94,6 +94,15 @@ flag sdl
   manual:
     True
 
+flag sdl-renderer
+  description:
+    Enable SDL Renderer backend (requires the SDL_RenderGeometry function available in SDL 2.0.18+).
+    The sdl configuration flag must also be enabled when using this flag.
+  default:
+    False
+  manual:
+    True
+
 flag glfw
   description:
     Enable GLFW backend.
@@ -240,12 +249,10 @@ library
   if flag(sdl)
     exposed-modules:
       DearImGui.SDL
-      DearImGui.SDL.Renderer
     build-depends:
       sdl2
     cxx-sources:
       imgui/backends/imgui_impl_sdl2.cpp
-      imgui/backends/imgui_impl_sdlrenderer2.cpp
 
     if os(windows) || os(darwin)
       extra-libraries:
@@ -262,6 +269,12 @@ library
       exposed-modules:
         DearImGui.SDL.Vulkan
 
+    if flag(sdl-renderer)
+      exposed-modules:
+        DearImGui.SDL.Renderer
+      cxx-sources:
+        imgui/backends/imgui_impl_sdlrenderer2.cpp
+
   if flag(glfw)
     exposed-modules:
       DearImGui.GLFW
@@ -365,7 +378,7 @@ executable sdlrenderer
   main-is: Renderer.hs
   hs-source-dirs: examples/sdl
   build-depends: sdl2, dear-imgui, managed, text
-  if (!flag(examples) || !flag(sdl))
+  if (!flag(examples) || !flag(sdl) || !flag(sdl-renderer))
     buildable: False
 
 executable vulkan