Disable Xbios video driver if FVDI present, but still allow it to be used when...

Disable Xbios video driver if FVDI present, but still allow it to be used when setting SDL_VIDEODRIVER

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%403227

src/video/xbios/SDL_xbios.c

@@ -53,6 +53,10 @@
 
 #define XBIOS_VID_DRIVER_NAME "xbios"
 
+#ifndef C_fVDI
+#define C_fVDI 0x66564449L
+#endif
+
 /* Debug print info */
 #if 0
 #define DEBUG_PRINT(what) \
@@ -95,6 +99,8 @@ static unsigned long	F30_palette[256];
 static int XBIOS_Available(void)
 {
 	unsigned long cookie_vdo, cookie_mil, cookie_hade, cookie_scpn;
+	unsigned long cookie_fvdi;
+	const char *envr = SDL_getenv("SDL_VIDEODRIVER");
 
 	/* Milan/Hades Atari clones do not have an Atari video chip */
 	if ( (Getcookie(C__MIL, &cookie_mil) == C_FOUND) ||
@@ -102,6 +108,17 @@ static int XBIOS_Available(void)
 		return 0;
 	}
 
+	/* fVDI means graphic card, so no Xbios with it */
+	if (Getcookie(C_fVDI, &cookie_fvdi) == C_FOUND) {
+		if (!envr) {
+			return 0;
+		}
+		if (SDL_strcmp(envr, XBIOS_VID_DRIVER_NAME)!=0) {
+			return 0;
+		}
+		/* Except if we force Xbios usage, through env var */
+	}
+
 	/* Cookie _VDO present ? if not, assume ST machine */
 	if (Getcookie(C__VDO, &cookie_vdo) != C_FOUND) {
 		cookie_vdo = VDO_ST << 16;