Automatically switch to variant engine supports

When XBoard is started with an engine that announces variants, but does
not lists normal or FRC amongst them, it switches to the first variant
that the engine announced (if not starting in a mode that involves other
engines or ICS). This will even take into account size overrides.

diff --git a/backend.c b/backend.c
index 839b44f..b440060 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -1564,6 +1564,23 @@ InitBackEnd3 P((void))
     char buf[MSG_SIZ];
     int err, len;
 
+    if(!appData.icsActive && !appData.noChessProgram && !appData.matchMode &&                         // mode involves only first engine
+       !strcmp(appData.variant, "normal") &&                                                          // no explicit variant request
+        appData.NrRanks == -1 && appData.NrFiles == -1 && appData.holdingsSize == -1 &&               // no size overrides requested
+       !SupportedVariant(first.variants, VariantNormal, 8, 8, 0, first.protocolVersion, "") &&        // but 'normal' won't work with engine
+       !SupportedVariant(first.variants, VariantFischeRandom, 8, 8, 0, first.protocolVersion, "") ) { // nor will Chess960
+       char c, *q = first.variants, *p = strchr(q, ',');
+       if(p) *p = NULLCHAR;
+       if(StringToVariant(q) != VariantUnknown) { // the engine can play a recognized variant, however
+           int w, h, s;
+           if(sscanf(q, "%dx%d+%d_%c", &w, &h, &s, &c) == 4) // get size overrides the engine needs with it (if any)
+               appData.NrFiles = w, appData.NrRanks = h, appData.holdingsSize = s, q = strchr(q, '_') + 1;
+           ASSIGN(appData.variant, q); // fake user requested the first variant played by the engine
+           Reset(TRUE, FALSE);         // and re-initialize
+       }
+       if(p) *p = ',';
+    }
+
     InitChessProgram(&first, startedFromSetupPosition);
 
     if(!appData.noChessProgram) {  /* [HGM] tidy: redo program version to use name from myname feature */