diff --git a/cogl/cogl-private.h b/cogl/cogl-private.h index b4ff42056..8f2a72e7f 100644 --- a/cogl/cogl-private.h +++ b/cogl/cogl-private.h @@ -75,6 +75,33 @@ _cogl_get_enable_legacy_state (void); int _cogl_pixel_format_get_bytes_per_pixel (CoglPixelFormat format); +/* + * _cogl_pixel_format_has_aligned_components: + * @format: a #CoglPixelFormat + * + * Queries whether the ordering of the components for the given + * @format depend on the endianness of the host CPU or if the + * components can be accessed using bit shifting and bitmasking by + * loading a whole pixel into a word. + * + * XXX: If we ever consider making something like this public we + * should really try to think of a better name and come up with + * much clearer documentation since it really depends on what + * point of view you consider this from whether a format like + * COGL_PIXEL_FORMAT_RGBA_8888 is endian dependent. E.g. If you + * read an RGBA_8888 pixel into a uint32 + * it's endian dependent how you mask out the different channels. + * But If you already have separate color components and you want + * to write them to an RGBA_8888 pixel then the bytes can be + * written sequentially regardless of the endianness. + * + * Return value: %TRUE if you need to consider the host CPU + * endianness when dealing with the given @format + * else %FALSE. + */ +gboolean +_cogl_pixel_format_is_endian_dependant (CoglPixelFormat format); + G_END_DECLS #endif /* __COGL_PRIVATE_H__ */ diff --git a/cogl/cogl.c b/cogl/cogl.c index d22a91faf..82a7f771a 100644 --- a/cogl/cogl.c +++ b/cogl/cogl.c @@ -1024,3 +1024,24 @@ _cogl_pixel_format_get_bytes_per_pixel (CoglPixelFormat format) return bpp_lut [format & 0xf]; } + +/* Note: this also refers to the mapping defined above for + * _cogl_pixel_format_get_bytes_per_pixel() */ +gboolean +_cogl_pixel_format_is_endian_dependant (CoglPixelFormat format) +{ + int aligned_lut[] = { -1, 1, 1, 1, + 0, 0, 0, -1, + 1, 1, -1, -1, + 0, 0, -1, -1}; + int aligned = aligned_lut[format & 0xf]; + + _COGL_RETURN_VAL_IF_FAIL (aligned != -1, FALSE); + + /* NB: currently checking whether the format components are aligned + * or not determines whether the format is endian dependent or not. + * In the future though we might consider adding formats with + * aligned components that are also endian independant. */ + + return aligned; +}