Since Graphics::loadThumbnail can return successfully when a thumbnail is skipped
the caller may want to check to the see that the thumbnail is not null before using
it. Setting it to null is just defensive in case the caller didn't do so.
If the user tries to use the thumbnail in setThumbnail then it will just
show a black screen for the thumbnail rather than crashing if they have
not set the thumbnail to null.
This commit introduces the following changes:
1. Graphics::loadThumbnail()
Now returns a boolean and takes a new argument skipThumbnail which
defaults to false. In case of true, loadThumbnail() reads past the
thumbnail data in the input stream instead of actually loading the
thumbnail. This simplifies savegame handling where, up until now,
many engines always read the whole savegame metadata (including
the thumbnail) and then threw away the thumbnail when not needed
(which is in almost all cases, the most common exception being
MetaEngine::querySaveMetaInfos() which is responsible for loading
savegame metadata for displaying it in the GUI launcher.
2. readSavegameHeader()
Engines which already implement such a method (name varies) now take
a new argument skipThumbnail (default: true) which is passed
through to loadThumbnail(). This means that the default case for
readSavegameHeader() is now _not_ loading the thumbnail from a
savegame and just reading past it. In those cases, e.g.
querySaveMetaInfos(), where we actually are interested in loading
the thumbnail readSavegameHeader() needs to explicitely be called
with skipThumbnail == false.
Engines whose readSavegameHeader() (name varies) already takes an
argument loadThumbnail have been adapted to have a similar
prototype and semantics.
I.e. readSaveHeader(in, loadThumbnail, header) now is
readSaveHeader(in, header, skipThumbnail).
3. Error handling
Engines which previously did not check the return value of
readSavegameHeader() (name varies) now do so ensuring that possibly
broken savegames (be it a broken thumbnail or something else) don't
make it into the GUI launcher list in the first place.
This fixes future issues like bug #3614654:
"ALL: ScummVM 1.5.0 can't read newer saved games".
There are a few behavior changes introduced with this commit:
- checkThumbnailHeader will now also report the presence of
unsupported/broken (but skippable) headers.
- skipThumbnail will also try to skip the data for broken/unsupported
thumbnail data.
- loadThumbnail will skip over broken/unsupported thumbnail data but still
return 0 in this case.
This allows any 2Bpp/4Bpp Surfaces to be written via saveThumbnail
and loadThumbnail now. It furthermore will preserve the loaded Surface
in loadThumbnail.
MKID_BE relied on unspecified behavior of the C++ compiler,
and as such was always a bit unsafe. The new MKTAG macro
is slightly less elegant, but does no longer depend on the
behavior of the compiler.
Inspired by FFmpeg, which has an almost identical macro.
- Extended SCUMM engine to support savegames without thumbnail header. (Increased savegame version to prevent saves to be loaded from older ScummVM versions)
- Fixed KYRA to properly support savegames without thumbnail header.
svn-id: r34054
