Use a symbolic constant for the default thread count.

src/Main/Config.hpp

@@ -16,12 +16,20 @@
 
 #define PERF_HUD 0       // Display time spent on vertex, setup and pixel processing for each thread
 #define PERF_PROFILE 0   // Profile various pipeline stages and display the timing in SwiftConfig
+
 #if defined(_WIN32)
 #define S3TC_SUPPORT 1
 #else
 #define S3TC_SUPPORT 0
 #endif
 
+// Worker thread count when not set by SwiftConfig
+// 0 = process affinity count (recommended)
+// 1 = rendering on main thread (no worker threads), useful for debugging
+#ifndef DEFAULT_THREAD_COUNT
+#define DEFAULT_THREAD_COUNT 0
+#endif
+
 enum
 {
 	PERF_PIXEL,

src/Main/SwiftConfig.cpp

@@ -726,7 +726,7 @@ namespace sw
 		config.perspectiveCorrection = ini.getBoolean("Quality", "PerspectiveCorrection", true);
 		config.transcendentalPrecision = ini.getInteger("Quality", "TranscendentalPrecision", 2);
 		config.transparencyAntialiasing = ini.getInteger("Quality", "TransparencyAntialiasing", 0);
-		config.threadCount = ini.getInteger("Processor", "ThreadCount", 0);
+		config.threadCount = ini.getInteger("Processor", "ThreadCount", DEFAULT_THREAD_COUNT);
 		config.enableSSE = ini.getBoolean("Processor", "EnableSSE", true);
 		config.enableSSE2 = ini.getBoolean("Processor", "EnableSSE2", true);
 		config.enableSSE3 = ini.getBoolean("Processor", "EnableSSE3", true);