[cairo] how to copy a part from one surface to another ?

[Carl Worth]

On Wed, 27 Jun 2007 11:57:31 +0200, wrote:
> destSurface->set_source(srcSurface, xDest, yDest, xSrc, ySrc, widthSrc, heightSrc)

I'll write in C, and hopefully you can trivially translate to your
language of interest. Given cr that's targeting dest_surface you can
do:

	cairo_set_source_surface (cr, src_surface, x_dest - x_src, y_dest - y_src);
	cairo_rectangle (cr, x_dest, y_dest, width, height);
	cairo_fill (cr);

If your source surface has any alpha, that will blend it over the
destination. If you want to copy the alpha directly, you'll want to
use the SOURCE operator something like this:

	cairo_save (cr);
	cairo_rectangle (cr, ...);
	cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
	cairo_fill (cr);
	cairo_restore (cr);

If your source surface has no alpha then you can use either one---it
doesn't matter.

And do notice that cairo isn't providing a "copy surface" primitive
here, but instead that you're simply drawing something and using a
surface as the source pattern. So you can similarly draw anything,
(complex polygons, text, etc.), and have it be patterned with the
surface.

Have fun with cairo,

-Carl
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