Re: Draft document-rendering tiling API to be called from viewer apps

On Wed, Jun 06, 2012 at 06:42:44PM +0100, Michael Meeks wrote:
> Hi guys,
>
> On Wed, 2012-06-06 at 16:33 +0100, Iain Billett wrote:
> > I haven't experimented but I've heard that not using power-of-two
> > lengths is seriously detrimental to performance.
>
>       Must make a mental note to ask a GPU hacker; in fact - lets do that :-)
> Luc - sorry to bother you with a quick question. For all these Android /
> portable 3D chipsets that you deal with - is it really true that we need
> to allocate power-of-two sized, preferably square textures ? [ we're
> working on rendering documents to bitmaps to manipulate them for a
> LibreOffice android viewer ].
>
> >  Considering we'll be using lots of resources to begin I think we
> > should make every reasonable optimisation
>
>       Sure; but say we have a Tablet, mine has 1280x800 resolution, are you
> seriously suggesting rounding 1280 up to 2048 ? and 800 up to 1024 ?
> giving a 2Mpixel texture instead of a 1Mpixel texture ;-) is that really
> going to be more fast/efficient. Presumably having a sane rowstride (eg.
> 1280) makes a ton of sense, but a power of two in each dimension ?
> Anyhow - Luc can give an authoritative answer :-)
>
> > Also, in this arrangement, It would be nice to have the dimensions of
> > the "document" area of the texture. Then if the rest of the bitmap is
> > fully transparent and the plane is too we can render a "page" alone
> > and keep track of dimensions. 
>
>       I guess.
>
> > My main concern with all this is in fact dealing with user interaction
> > i.e. mapping measurements in pixels to OpenGL coordinates. This is
> > more of a problem for editing, though. 
>
>       Yep.
>
> > Also, are we intending to have continuous scroll documents ( with all
> > the pages available via scroll - like most desktop applications ) or
> > would we be happy to have users flick (or otherwise) through pages. I
> > think the latter would make it easier to manage resources for large
> > documents.
>
>       I think we'll want to flick through pages when we have them :-) For
> spreadsheets of course we don't really have that (hence liking doubles
> for positioning the view-pane incidentally).
>
>       Thanks !
>
>               Michael.

Not sure whether it is so detrimental for performance, I guess it 
depends on the hw and driver implementation. And yes, it depends on the 
GL version whether non-power-of-two textures are accepted.

For the record, i am not such a big 3D/GPU buff, most of my experience 
is with display stuff, some 2d accel/video/mpeg, and tons of lowlevel 
things. My actual GPU knowledge is mostly limited to what was shown at 
linuxtag a few weeks ago, where i was, once again, filling in the bottom 
end bits. My knowledge of openGL* is extremely limited, and this 
question is more for someone who has used GL on a variety of drivers and 
hardware, than for someone who fills in the bottom bits :)

Luc Verhaegen.