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Re: AGG Drawing on Planar Buffer

by Stephan Assmus :: Rate this Message:

On 2009-06-18 at 16:25:50 [+0200], NickMtl <valerianmusic@...> wrote:

> I'm trying to use AGG to draw on a image buffer where the RGB values are
> stored as:
>
> "r1,r2,r3, g1,g2,g3, b1,b2,b3, ..." (Planar)
>
> instead of:
>
> "r1,g1,b1, r2,g2,b2, ..." (Interleaved).
>
> I remember reading a while back that AGG could be made to do this using
> grayscale formats, but I can't find any details on this.
>
> Anyone can give me an idea how to do this?

IIRC, the RGB blending operations indeed rely on interleaved image data.
All the code I have seen gets a pointer to a pixel at a certain offset and
then assumes interleaved data, offsets depend on ordertype. So you have two
options:

1) Use three individual buffers of "agg::pixfmt_alpha_blend_gray" with
"Step" and "Offset" according to your needs (I guess at least Step will
remain 1). And then do any rendering three times. You would probably also
have to separate the input colors accordingly. :-\

2) Duplicate the RGB pixel format implementation that matches the features
you need, and change all the code that refers to order_type and accesses
color channels using that, and make these places use offsets which are
settable members of the object. The increments for pixels will also be
different (i.e. just 1 instead of 4 and so on). Another option is to change
the code so that it uses three or four different agg::rendering_buffers for
each channel.

I think option 2 will be much better, since you should be able to use
everything else as before, except for image filters/accessors, I would
guess.

Best regards,
-Stephan

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