[MPlayer-dev-eng] [PATCH] A new ASS renderer

[wm4]

On Sun, 23 Sep 2012 16:37:20 +0200
Reimar Döffinger <Reimar.Doeffinger at gmx.de> wrote:

> I am afraid that will depend on a lot of things.
> For example how fast the driver is at creating a new texture vs.
> just updating one.
> Some drivers for example also have huge issues with memory
> fragmentation when allocating and freeing huge textures of different
> sizes all the time.
> Then there's also a question whether it's a subtitle where things
> change all the time or one where 90% stays the same and a small thing
> changes (in which case I suspect your approach would waste a good bit
> of memory bandwidth? Here integrated vs. dedicated GPU can make a lot
> of difference if that's a problem).
> Lastly, if the driver decides to use a host-memory backing texture,
> the glTexSubImage calls can be almost as fast as a memcpy, but that
> relies heavily on driver details.

The number of people who tested my changes is probably rather low, but
I haven't heard of any negative reports yet. It seems to be an overall
improvement.

I was thinking a relatively easy way to improve upon this would be
making libass export cache info (like assigning each sub-image a unique
ID), and then using a ringbuffer of textures: on each frame, you'd
upload a frame's new sub-images to a texture. Images that are already
uploaded to an old texture could be reused. If the current texture is
full, go to the next one in the ringbuffer, flush all old images, and
reupload all what's needed.

Just a random idea. Didn't bother with it, because again, it would
probably be a useless optimization.

In general, with libass, you have two types of frames: 1. practically
static and rather small, and 2. *Everything* changes, can happen with
all sizes. What's the often cited case where only a "small" thing
changes, but there's a significant amount of other images that are
still static? Or in other words, a case where a clever caching scheme
would actually help a lot.

And again, most time is spent in libass, not uploading or rendering the
sub-images. Or does anyone have different experiences? I'd like to hear
of it. Maybe I'm missing something.