vlc_es: add a function to get the mask for RGB chromas

Even if we don't keep masks internally, some system still need to
set RGB(A) masks. We can handle all our RGB chroma as we know
the proper component position.

include/vlc_es.h

@@ -783,4 +783,71 @@ vlc_es_id_GetStrId(vlc_es_id_t *id);
 VLC_API enum es_format_category_e
 vlc_es_id_GetCat(vlc_es_id_t *id);
 
+/**
+ * Get the native endianness mask for a RGB fourcc
+ *
+ * @note the alpha mask is 0 when the chroma doesn't contain an alpha component.
+ *
+ * @return VLC_SUCCESS if the mask values were filled
+ */
+static inline int vlc_RGBChromaToMask( vlc_fourcc_t fcc, uint32_t *rmask,
+                                       uint32_t *gmask, uint32_t *bmask,
+                                       uint32_t *amask )
+{
+    switch(fcc)
+    {
+        case VLC_CODEC_BGRA:
+            *bmask = 0xff000000;
+            *gmask = 0x00ff0000;
+            *rmask = 0x0000ff00;
+            *amask = 0x000000ff;
+            break;
+        case VLC_CODEC_BGRX:
+            *bmask = 0xff000000;
+            *gmask = 0x00ff0000;
+            *rmask = 0x0000ff00;
+            *amask = 0;
+            break;
+        case VLC_CODEC_RGBA:
+            *rmask = 0xff000000;
+            *gmask = 0x00ff0000;
+            *bmask = 0x0000ff00;
+            *amask = 0x000000ff;
+            break;
+        case VLC_CODEC_RGBX:
+            *rmask = 0xff000000;
+            *gmask = 0x00ff0000;
+            *bmask = 0x0000ff00;
+            *amask = 0;
+            break;
+        case VLC_CODEC_ABGR:
+            *amask = 0xff000000;
+            *bmask = 0x00ff0000;
+            *gmask = 0x0000ff00;
+            *rmask = 0x000000ff;
+            break;
+        case VLC_CODEC_XBGR:
+            *amask = 0;
+            *bmask = 0x00ff0000;
+            *gmask = 0x0000ff00;
+            *rmask = 0x000000ff;
+            break;
+        case VLC_CODEC_ARGB:
+            *amask = 0xff000000;
+            *rmask = 0x00ff0000;
+            *gmask = 0x0000ff00;
+            *bmask = 0x000000ff;
+            break;
+        case VLC_CODEC_XRGB:
+            *amask = 0;
+            *rmask = 0x00ff0000;
+            *gmask = 0x0000ff00;
+            *bmask = 0x000000ff;
+            break;
+        default:
+            return VLC_EINVAL;
+    }
+    return VLC_SUCCESS;
+}
+
 #endif