video: Don't use texture framebuffer on Windows Subsystem for Linux.

Reference Issue #6333.

src/video/SDL_video.c

@@ -56,6 +56,13 @@
 #include <emscripten.h>
 #endif
 
+#ifdef __LINUX__
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#endif
+
+
 /* Available video drivers */
 static VideoBootStrap *bootstrap[] = {
 #if SDL_VIDEO_DRIVER_COCOA
@@ -2640,6 +2647,15 @@ SDL_CreateWindowFramebuffer(SDL_Window * window)
             attempt_texture_framebuffer = SDL_FALSE;
         }
 
+#if defined(__LINUX__)
+        /* On WSL, direct X11 is faster than using OpenGL for window framebuffers, so try to detect WSL and avoid texture framebuffer. */
+        else if ((_this->CreateWindowFramebuffer != NULL) && (SDL_strcmp(_this->name, "x11") == 0)) {
+            struct stat sb;
+            if ((stat("/proc/sys/fs/binfmt_misc/WSLInterop", &sb) == 0) || (stat("/run/WSL", &sb) == 0)) { /* if either of these exist, we're on WSL. */
+                attempt_texture_framebuffer = SDL_FALSE;
+            }
+        }
+#endif
 #if defined(__WIN32__) || defined(__WINGDK__) /* GDI BitBlt() is way faster than Direct3D dynamic textures right now. (!!! FIXME: is this still true?) */
         else if ((_this->CreateWindowFramebuffer != NULL) && (SDL_strcmp(_this->name, "windows") == 0)) {
             attempt_texture_framebuffer = SDL_FALSE;