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[Gnash-dev] Renderer transparency

From: Benjamin Wolsey
Subject: [Gnash-dev] Renderer transparency
Date: Fri, 29 Aug 2008 08:22:26 +0200

> revno: 9648
> committer: Benjamin Wolsey <address@hidden>
> branch nick: trunk
> timestamp: Thu 2008-08-28 21:59:28 +0200
> message:
>   Convert VP6A video to image::ImageRGBA. This only succeeds with SwScale,
>   not with older versions of ffmpeg.
>   Make renderers accept but ignore RGBA data. It is easy to get agg to render
>   the RGBA images, slightly harder to get it to handle both RGB and RGBA, and
>   so far I don't see how to get it to handle transparency correctly.

Can anyone sort out renderer transparency handling? There are now lots
of occasions when transparency is needed and displaying it either isn't
implemented or often looks rubbish. At the moment, most of the code for
reading and using transparent images is there in the core, but the
renderers can't handle it.

With video, RGBA images will display if, in
render_handler_agg::drawVideoFrame(), you change line 453,

    typedef agg::pixfmt_rgb24_pre baseformat;

    typedef agg::pixfmt_rgba32_pre baseformat;

But they are solid, and obviously it ruins display of rgb images. I
can't be sure that the transparency information is read correctly by
ffmpeg, but I can be sure that changing the alpha element makes no
difference to the display.

Display of transparent bitmap characters (e.g. dynamically loaded PNG)
is still waiting to be corrected too. This works but is faulty. Again,
it might be the way the alpha data is read and not the fault of the
renderer (though I don't think so), but until someone familiar with the
renderer code looks at it, I won't know. I assumed that being able to
load PNG images directly, as is possible since a couple of weeks ago,
would make testing and debugging easier.

There are various open bug items related to this.

It is necessary to have a version of ffmpeg with swscale for decoding
VP6A video to RGBA.

I can provide useful SWFs for testing, ming source code and videos if
anyone is interested in doing it. It would be very good to have it for
the next release.


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