GDIPlus - add a webp image decoder ?

[R.Wieser]

Hello all,

Some time ago I stumbled over a few webp images. After some some
websearching I found a dll which could decode them into a raw byte arrays,
and with help of GDI+ I was able to save that into a native format (jpg,
png, etc), allowing me to view the resulting images.


While doing the above I was (again) made aware that GDI+ has(?) installable
image decoders & encoders. So, I thought it would be an idea to see if I
could write-and-install a webp decoder to that list.

The thing is, I can't seem to find anything of worth regarding native GDI+
installable image decoders, and only very little about a WIC type of
decoder. At least not enough to be able to get a complete picture about
what needs to be done.


So, I'm wondering if anyone here knows anything about how to create,
preferrably, a native GDI+ decoder - though information about how to create
WIC type of decoder is quite welcome too. (I'm an Assembly programmer, which
is why I rather work with the former than the latter)

Regards,
Rudy Wieser

[JJ]

You can learn from examples, such as below PGM WIC codec.

https://github.com/vbaderks/netpbm-wic-codec

[R.Wieser]

JJ,

>> So, I'm wondering if anyone here knows anything about how to create,
>> preferrably, a native GDI+ decoder - though information about how to
>> create
>> WIC type of decoder is quite welcome too. (I'm an Assembly programmer,
>> which
>> is why I rather work with the former than the latter)

> You can learn from examples, such as below PGM WIC codec.
>
> https://github.com/vbaderks/netpbm-wic-codec

Thanks for the link.

Thoug part of the problem with the WIC style approach is that I would need
to figure out what the methods and properties of each of the used objects is
(in vtable order!) - which is normally not something thats part of such an
example.

(I've had to do similar often enough to know its a hit-or-miss kind of thing
trying to google for it ...)

Nonetheless, its more than I had before. :-)

Regards,
Rudy Wieser

[JJ]

On Mon, 27 Nov 2023 08:08:45 +0100, R.Wieser wrote:
>
> Thanks for the link.
>
> Thoug part of the problem with the WIC style approach is that I would need
> to figure out what the methods and properties of each of the used objects is
> (in vtable order!) - which is normally not something thats part of such an
> example.
>
> (I've had to do similar often enough to know its a hit-or-miss kind of thing
> trying to google for it ...)
>
> Nonetheless, its more than I had before. :-)

AFAIK, in the reference part of Microsoft SDK documentations, the list of
methods of an interface is always in VTable order. You can still check the
relevant C header file if you have doubts.

[R.Wieser]

JJ,

> AFAIK, in the reference part of Microsoft SDK documentations, the
> list of methods of an interface is always in VTable order. You can
> still check the relevant C header file if you have doubts.

As mentioned, I've googled quite a bit in search of how to "talk to"
objects. And it always was a problem finding the vtbale information, even
for common MS objects.

But if you know where I can find on-line Microsoft SDK documentation I would
be much obliged.

Currently the most pertinent information I can find is learn.microsoft.com,
but even that one has its problems. Just yesterday I was having a problem
with a standard GDI+ function, GdipCreateBitmapFromScan0 . Try to find some
MS documentation about it (and its sibblings) and you get nowhere fast. :-(

Regards,
Rudy Wieser