[cairo] PNG and transparent background

[Uli Schlachter]

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Am 29.01.2011 20:54, Петрищенко Анатолий wrote:
> 
> Hello,
> I have a very simple problem. I'm using cairo to draw some text and save it to png format file,using cairo_surface_write_to_png. But, I can't make background transparent. I  think, I simply don't get an idea of doing that.
[...]
> cairo_save(m_cr);
> 	cairo_set_operator(m_cr,CAIRO_OPERATOR_SOURCE);
> 	cairo_set_source_rgba(m_cr,1.0,1.0,1.0,0.0);
> 	cairo_paint(m_cr);
> 	cairo_restore(m_cr);
> In all cases, all I've got is a white opaque background. What can be used to perform this trick?

Hi,

no idea what you might be doing wrong, but attached is a small app which
generates a file "out.png" with a transparent background using the operations
you gave above.

I hope this helps you figuring your problem out.

Cheers,
Uli
- -- 
"Do you know that books smell like nutmeg or some spice from a foreign land?"
                                                  -- Faber in Fahrenheit 451
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