Add an isALPHA macro to check if pixel format has alpha channel

git-svn-id: file:///var/local/repositories/mplayer/trunk/libswscale@28747 b3059339-0415-0410-9bf9-f77b7e298cf2

swscale_internal.h

@@ -273,6 +273,13 @@ const char *sws_format_name(int format);
         || (x)==PIX_FMT_MONOBLACK   \
         || (x)==PIX_FMT_MONOWHITE   \
     )
+#define isALPHA(x)      (           \
+           (x)==PIX_FMT_BGR32       \
+        || (x)==PIX_FMT_BGR32_1     \
+        || (x)==PIX_FMT_RGB32       \
+        || (x)==PIX_FMT_RGB32_1     \
+        || (x)==PIX_FMT_YUVA420P    \
+    )
 
 static inline int fmt_depth(int fmt)
 {