Fixed bug 3273 - Fix for slow video subsystem initialization when using XRandR.

Mart?n Golini

I'm having a very slow initialization of the video subsystem that locks the window creation for about 500 ms ( tested in at least 4 different systems ). What i found is that X11_InitModes_XRandR is using XRRGetScreenResources, that explicitly ask to poll the hardware for changes. This is not really necessary since if the data is already available you can use XRRGetScreenResourcesCurrent.
I attached a tentative patch that fix this issue. With the patch there's no lock when the subsystem is initialized and the window creation is instant in my applications. The patch only uses XRRGetScreenResourcesCurrent in X11_InitModes_XRandR but it could be potentially used in X11_GetDisplayModes and X11_SetDisplayMode.

src/video/x11/SDL_x11modes.c

@@ -396,9 +396,16 @@ X11_InitModes_XRandR(_THIS)
                 X11_XFree(pixmapformats);
             }
 
-            res = X11_XRRGetScreenResources(dpy, RootWindow(dpy, screen));
-            if (!res) {
-                continue;
+            res = X11_XRRGetScreenResourcesCurrent(dpy, RootWindow(dpy, screen));
+            if (!res || res->noutput == 0) {
+                if (res) {
+                    X11_XRRFreeScreenResources(res);
+                }
+
+                res = X11_XRRGetScreenResources(dpy, RootWindow(dpy, screen));
+                if (!res) {
+                    continue;
+                }
             }
 
             for (output = 0; output < res->noutput; output++) {

src/video/x11/SDL_x11sym.h

@@ -292,6 +292,7 @@ SDL_X11_SYM(void,XRRFreeScreenConfigInfo,(XRRScreenConfiguration *config),(confi
 SDL_X11_SYM(void,XRRSetScreenSize,(Display *dpy, Window window,int width, int height,int mmWidth, int mmHeight),(dpy,window,width,height,mmWidth,mmHeight),)
 SDL_X11_SYM(Status,XRRGetScreenSizeRange,(Display *dpy, Window window,int *minWidth, int *minHeight, int *maxWidth, int *maxHeight),(dpy,window,minWidth,minHeight,maxWidth,maxHeight),return)
 SDL_X11_SYM(XRRScreenResources *,XRRGetScreenResources,(Display *dpy, Window window),(dpy, window),return)
+SDL_X11_SYM(XRRScreenResources *,XRRGetScreenResourcesCurrent,(Display *dpy, Window window),(dpy, window),return)
 SDL_X11_SYM(void,XRRFreeScreenResources,(XRRScreenResources *resources),(resources),)
 SDL_X11_SYM(XRROutputInfo *,XRRGetOutputInfo,(Display *dpy, XRRScreenResources *resources, RROutput output),(dpy,resources,output),return)
 SDL_X11_SYM(void,XRRFreeOutputInfo,(XRROutputInfo *outputInfo),(outputInfo),)