consolidate SDL icon changing code

stepmania/src/SDL_utils.cpp

@@ -510,3 +510,22 @@ bool SDL_GetEvent(SDL_Event &event, int mask)
 }
 
 
+#include "SDL_image.h"	// for setting icon
+#include "SDL_rotozoom.h"	// for setting icon
+
+void mySDL_WM_SetIcon( CString sIconFile )
+{
+	SDL_Surface *srf = IMG_Load(sIconFile);
+	SDL_SetColorKey( srf, SDL_SRCCOLORKEY, SDL_MapRGB(srf->format, 0xFF, 0, 0xFF));
+
+	/* Windows icons are 32x32 and SDL can't resize them for us, which
+	 * causes mask corruption.  (Actually, the above icon *is* 32x32;
+	 * this is here just in case it changes.) */
+	ConvertSDLSurface(srf, srf->w, srf->h,
+		32, 0xFF000000, 0x00FF0000, 0x0000FF00, 0x000000FF);
+	zoomSurface(srf, 32, 32);
+
+	SDL_SetAlpha( srf, SDL_SRCALPHA, SDL_ALPHA_OPAQUE );
+	SDL_WM_SetIcon(srf, NULL /* derive from alpha */);
+	SDL_FreeSurface(srf);
+}