Turned the X11 mode extension environment variables into hints so the…

…y can be more easily set from applications.

include/SDL_hints.h

@@ -118,7 +118,40 @@ extern "C" {
  *  By default SDL does not sync screen surface updates with vertical refresh.
  */
 #define SDL_HINT_RENDER_VSYNC               "SDL_RENDER_VSYNC"
-
+
+/**
+ *  \brief  A variable controlling whether the X11 VidMode extension should be used.
+ *
+ *  This variable can be set to the following values:
+ *    "0"       - Disable XVidMode
+ *    "1"       - Enable XVidMode
+ *
+ *  By default SDL will use XVidMode if it is available.
+ */
+#define SDL_HINT_VIDEO_X11_XVIDMODE         "SDL_VIDEO_X11_XVIDMODE"
+
+/**
+ *  \brief  A variable controlling whether the X11 Xinerama extension should be used.
+ *
+ *  This variable can be set to the following values:
+ *    "0"       - Disable Xinerama
+ *    "1"       - Enable Xinerama
+ *
+ *  By default SDL will use Xinerama if it is available.
+ */
+#define SDL_HINT_VIDEO_X11_XINERAMA         "SDL_VIDEO_X11_XINERAMA"
+
+/**
+ *  \brief  A variable controlling whether the X11 XRandR extension should be used.
+ *
+ *  This variable can be set to the following values:
+ *    "0"       - Disable XRandR
+ *    "1"       - Enable XRandR
+ *
+ *  By default SDL will use XRandR if it is available.
+ */
+#define SDL_HINT_VIDEO_X11_XRANDR           "SDL_VIDEO_X11_XRANDR"
+
 /**
  *  \brief  A variable controlling whether the idle timer is disabled on iOS.
  *

src/video/x11/SDL_x11modes.c

@@ -22,6 +22,7 @@
 
 #if SDL_VIDEO_DRIVER_X11
 
+#include "SDL_hints.h"
 #include "SDL_x11video.h"
 
 /*#define X11MODES_DEBUG*/
@@ -270,10 +271,10 @@ CheckXinerama(Display * display, int *major, int *minor)
     *major = *minor = 0;
 
     /* Allow environment override */
-    env = getenv("SDL_VIDEO_X11_XINERAMA");
+    env = SDL_GetHint(SDL_HINT_VIDEO_X11_XINERAMA);
     if (env && !SDL_atoi(env)) {
 #ifdef X11MODES_DEBUG
-        printf("Xinerama disabled due to environment variable\n");
+        printf("Xinerama disabled due to hint\n");
 #endif
         return SDL_FALSE;
     }
@@ -311,10 +312,10 @@ CheckXRandR(Display * display, int *major, int *minor)
     *major = *minor = 0;
 
     /* Allow environment override */
-    env = getenv("SDL_VIDEO_X11_XRANDR");
+    env = SDL_GetHint(SDL_HINT_VIDEO_X11_XRANDR);
     if (env && !SDL_atoi(env)) {
 #ifdef X11MODES_DEBUG
-        printf("XRandR disabled due to environment variable\n");
+        printf("XRandR disabled due to hint\n");
 #endif
         return SDL_FALSE;
     }
@@ -350,10 +351,10 @@ CheckVidMode(Display * display, int *major, int *minor)
     *major = *minor = 0;
 
     /* Allow environment override */
-    env = getenv("SDL_VIDEO_X11_XVIDMODE");
+    env = SDL_GetHint(SDL_HINT_VIDEO_X11_XVIDMODE);
     if (env && !SDL_atoi(env)) {
 #ifdef X11MODES_DEBUG
-        printf("XVidMode disabled due to environment variable\n");
+        printf("XVidMode disabled due to hint\n");
 #endif
         return SDL_FALSE;
     }