Add a macro for querying the byte order of SkPMColor.

R=reed@google.com

Author: bsalomon@google.com

Reviewed By: reed@google.com,epoger@google.com

Review URL: https://chromiumcodereview.appspot.com/12771010

git-svn-id: http://skia.googlecode.com/svn/trunk@8219 2bbb7eff-a529-9590-31e7-b0007b416f81

include/core/SkPostConfig.h

@@ -187,6 +187,28 @@
     #endif
 #endif
 
+/**
+ * SK_PMCOLOR_BYTE_ORDER can be used to query the byte order of SkPMColor at compile time. The
+ * relationship between the byte order and shift values depends on machine endianness. If the shift
+ * order is R=0, G=8, B=16, A=24 then ((char*)&pmcolor)[0] will produce the R channel on a little
+ * endian machine and the A channel on a big endian machine. Thus, given those shifts values,
+ * SK_PMCOLOR_BYTE_ORDER(R,G,B,A) will be true on a little endian machine and
+ * SK_PMCOLOR_BYTE_ORDER(A,B,G,R) will be true on a big endian machine.
+ */
+#ifdef SK_CPU_BENDIAN
+    #define SK_PMCOLOR_BYTE_ORDER(C0, C1, C2, C3)     \
+        (SK_ ## C3 ## 32_SHIFT == 0  &&             \
+         SK_ ## C2 ## 32_SHIFT == 8  &&             \
+         SK_ ## C1 ## 32_SHIFT == 16 &&             \
+         SK_ ## C0 ## 32_SHIFT == 24)
+#else
+    #define SK_PMCOLOR_BYTE_ORDER(C0, C1, C2, C3)     \
+        (SK_ ## C0 ## 32_SHIFT == 0  &&             \
+         SK_ ## C1 ## 32_SHIFT == 8  &&             \
+         SK_ ## C2 ## 32_SHIFT == 16 &&             \
+         SK_ ## C3 ## 32_SHIFT == 24)
+#endif
+
 //  stdlib macros
 
 #if 0

include/gpu/GrTypes.h

@@ -291,11 +291,9 @@ enum GrPixelConfig {
 #ifndef SK_CPU_LENDIAN
     #error "Skia gpu currently assumes little endian"
 #endif
-#if 24 == SK_A32_SHIFT && 16 == SK_R32_SHIFT && \
-     8 == SK_G32_SHIFT &&  0 == SK_B32_SHIFT
+#if SK_PMCOLOR_BYTE_ORDER(B,G,R,A)
     static const GrPixelConfig kSkia8888_GrPixelConfig = kBGRA_8888_GrPixelConfig;
-#elif 24 == SK_A32_SHIFT && 16 == SK_B32_SHIFT && \
-       8 == SK_G32_SHIFT &&  0 == SK_R32_SHIFT
+#elif SK_PMCOLOR_BYTE_ORDER(R,G,B,A)
     static const GrPixelConfig kSkia8888_GrPixelConfig = kRGBA_8888_GrPixelConfig;
 #else
     #error "SK_*32_SHIFT values must correspond to GL_BGRA or GL_RGBA format."