On Thu, 22 Jun 2006 13:45:45 +0900 (JST)
Masatake YAMATO <[EMAIL PROTECTED]> wrote:
>After rethinking, I found a case that FT_Err_Unimplemented is not
>enough. With current code, FT_Err_Unimplemented is returned even if a
>bdf face is passed to FT_TrueTypeGX_Validate. From the return value
>the user cannot distinguish (1) a validator is just disabled when building
>libfreetype2 nor (2) a validator service doesn't support the face
>passed as an argument.
>
>With following patch FT_TrueTypeGX_Validate returns
>FT_Err_Unimplemented_Feature
>for the case (1); and FT_Err_Invalid_Argument for the case (2).
>
>Toshiya-san and Werner, do you think this is over kill?
Looking other modules, it seems that yet we have not
decided the policy to follow.
For example, src/base/ftwinfnt.c for WinFNT driver
has function like this:
FT_EXPORT_DEF( FT_Error )
FT_Get_WinFNT_Header( FT_Face face,
FT_WinFNT_HeaderRec *header )
{
FT_Service_WinFnt service;
FT_Error error;
error = FT_Err_Invalid_Argument;
if ( face != NULL )
{
FT_FACE_LOOKUP_SERVICE( face, service, WINFNT );
if ( service != NULL )
{
error = service->get_header( face, header );
}
}
return error;
}
Here, we cannot discriminate between the error is because
"WinFNT support is not builtin" or because "invalid face
(e.g. BDF) is passed to WinFNT driver".
David, Werner and Yamato-san, I think it's time to decide
a policy. I have 2 ideas in following, which is better?
Policy A:
Direct call of FT_XXX() does not return reliable
information about the availability of functionality,
although the interface of excluded module must return
SOME error. The availability should be checked by FT_Get_Module().
Policy B:
Direct call of FT_XXX() returns the information
about the availability of functionality. To discriminate
between "no driver" and "driver exists but unimplemented
feature is requested", FT_Err_Unimplemented_Feature should
not be used to return an error caused by builtin modules.
For example, following usage should be fixed - because
FNT_Size_Request() is built, and the error is caused by
invalid flag.
static FT_Error
FNT_Size_Request( FT_Size size,
FT_Size_Request req )
{
FNT_Face face = (FNT_Face)size->face;
FT_WinFNT_Header header = &face->font->header;
FT_Bitmap_Size* bsize = size->face->available_sizes;
FT_Error error = FNT_Err_Invalid_Pixel_Size;
FT_Long height;
height = FT_REQUEST_HEIGHT( req );
height = ( height + 32 ) >> 6;
switch ( req->type )
{
case FT_SIZE_REQUEST_TYPE_NOMINAL:
if ( height == ( bsize->y_ppem + 32 ) >> 6 )
error = FNT_Err_Ok;
break;
case FT_SIZE_REQUEST_TYPE_REAL_DIM:
if ( height == header->pixel_height )
error = FNT_Err_Ok;
break;
default:
error = FNT_Err_Unimplemented_Feature;
break;
}
if ( error )
return error;
else
return FNT_Size_Select( size );
}
-------------
I think, although policy A is theoretically right, I prefer
policy B. Because, it is easy for LD_PRELOAD trick to rewrite
disabled FT_Get_WinFNT_Header() to working one, but it is
difficult to rewrite FT_Get_Module() with disabled WinFNT.
Yet I've not made such demos, it's just conceive.
Regards,
mpsuzuki
_______________________________________________
Freetype-devel mailing list
Freetype-devel@nongnu.org
http://lists.nongnu.org/mailman/listinfo/freetype-devel
