[osg-submissions] Bug in MRT and FBO

[Robert Osfield]

Thanks Art, changes now merged and submitted to SVN.

On Tue, Jul 15, 2008 at 1:34 PM, Art Tevs <stud_info2 at yahoo.de> wrote:
> Hi Robert, J.P.
>
>
> Ok, Robert, I think you ahve to remove the ambiguosity of using GLenum then form the source code. In my application I now just do write something like this:
>
>                    fbo->setAttachment(osg::Camera::BufferComponent(osg::Camera::COLOR_BUFFER0 + i), ...)
>
> which do the work. I am not a friend of non-clean c-code, however I can live with that solution. (I see that it is also often used in osg sources, hence who cares ;) )
>
> I have attached the patche FrameBufferObject files, to remove the ambiguosity of using GLenum. now user have no possibility to use GLenums anymore. Check it out.
>
>
> Best regards,
> Art
>
> --- Robert Osfield <robert.osfield at gmail.com> schrieb am Di, 15.7.2008:
>
>> Von: Robert Osfield <robert.osfield at gmail.com>
>> Betreff: Re: [osg-submissions] Bug in MRT and FBO
>> An: stud_info2 at yahoo.de
>> Datum: Dienstag, 15. Juli 2008, 13:37
>> Hi Art,
>>
>> On Tue, Jul 15, 2008 at 12:15 PM, Art Tevs
>> <stud_info2 at yahoo.de> wrote:
>> > for (int i=0; i < 4; i++)
>> >   fbo->setAttachment(GL_COLOR_BUFFER0_EXT + i,
>> ...);
>> > , which is correct in respect to OpenGL
>> specificatiosn, since GL_COLOR_BUFFERn_EXT =
>> GL_COLOR_BUFFER0_EXT + n.
>> >
>> >
>> > If you remove the GLenum then one has to write
>> something like this:
>> >
>> > for (int i=0; i < 4; i++)
>> >
>> fbo->setAttachment(Camera::BufferAttachment(int(Camera::COLOR_BUFFER0)
>> + i), ...);
>> >
>> > which ends up in a lot of casts, which is not so nice
>> code style (one can not add integer value to an enum
>> value).
>>
>> Perhaps allow ints, but no GLenum would allow you to avoid
>> the
>> casting.   Another perspective is that it wouldn't
>> expect most users
>> ever to directly use FBO's so this isn't a big
>> issue to for most
>> users.
>>
>> > Hence I would propose to let the GLenum in there or to
>> work out a new API interface to solve that problem.
>>
>> More API isn't really solving a problem, its just
>> creating more
>> potential problems in usage/maintenance and understanding.
>> I would
>> like to simplify things and avoid gotcha's like
>> you've come across.
>>
>>
>> > P.S. Sorry, I do not remember the discussion about the
>> using of COLOR_BUFFER!=COLOR_BUFFER0. I can not see any
>> issue which might be introduced by setting
>> COLOR_BUFFER=COLOR_BUFFER0. Could you explain me in few
>> words why?
>>
>> The discussion will be in the archives.  The upshot is that
>> with MRT
>> you really need to explicitly select it, rather than
>> implicitly
>> setting it as was done previously.  The rule now is the if
>> you want to
>> use MRT you have to use COLOR_BUFFER0 rather than
>> COLOR_BUFFER, as
>> COLOR_BUFFER is the non MRT FBO path.  This clears up any
>> ambiguity of
>> whether you need to enable MRT or not.  The problem case
>> before was
>> when you had only have COLOR_BUFFER and FBO would then not
>> know
>> whether to enable MRT or not, this caused bugs.
>>
>> Robert.
>>
>> Robert.
>
>
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