On 01-Jun-01 Ben Bridgwater wrote:
> "Nemosoft Unv." wrote:
>
>> On 31-May-01 Ben Bridgwater wrote:
> Not really - just add flags to indicate what processor attributes (MMX
> etc) each converter needs, order the accelerated converters before the
> others, then scan the list for the first matching one suported by the
> actual processor attributes.
>
> I'm open to suggestion.
I would simply replace the function pointer with the most optimized
function during initialization; that way the logic in GetConvertor can be
kept really simple (otherwise, you´d end up with a different GetConvertor on
each platform!).
Some pseudo code might clarify:
library_init()
{
/* All C functions */
register_convertor(YUV420, RGB, yuv420_rgb_C);
register_convertor(RGB, YUV420, rgb_yuv420_C);
register_convertor(YUYV, RGB, yuyv_rgb_C);
/* some assembly functions */
register_convertor(YUV420, RGB, yuv420_rgb_x86);
register_convertor(RGB, YUV420, rbg_yuv420_x86);
/* MMX optimized */
register_convertor(YUV420, RGB, yuv420_rgb_x86_mmx);
}
get_convertor(int from, int to)
{
.. search list for the combination ...
while (conv)
if (conv->from == from && conv->to == to)
return conv->function;
}
register_convertor would replace the function in it´s list, and no additional
logic would need to be present in get_convertor at all. Adding a convertor
would simply be a matter of implementing it, and adding it to the end of
library_init. Simple.
> I guess I *could* delete the "static" ;-)
>
> If you're thinking of converter chains, then better just to guarantee
> converters to/from a couple of intermendiate formats such as RGB24 or
> I420.
I´m rather thinking about a program that´s being confronted with a
combination that´s not available, and wants to select a good alternative.
But we´ll see if this really will be a problem.
> For these formats "to" is useful for X display, and "from" is useful for
> V4L and AVI. You're right that's the way it's implemented - as a bunch
> of individual converters that cover the common XImage formats, but the
> point is that the app can just do a dumb "descriptor.format = PackedRGB,
> descriptor.r/g/b masks = XImage.r/g/b masks", then ask for a converter
> to/from that format.
So you have a ´general purpose´ convertor that can convert to almost
anything (at the price of being slow, presumably)?
- Nemosoft
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