[Ipe-discuss] Transparency/background color and iperender -png

[Otfried Cheong]

>> If you can recompile iperender, you can easily achieve this by changing
>> the line
>>
>>        *p++ = 0xffffffff;
>>
>> in iperender.cpp to:
>>
>>        *p++ = 0x00ffffff;
>
> Thank you very much for this pointer!
>
> I think the correct value to use is 0x00000000 since cairo uses
> pre-multiplied alpha:
> http://cairographics.org/manual/cairo-Image-Surfaces.html#cairo-format-t
>
> Using 0x0000000 works perfectly for me, while using 0x00ffffff gives a
> transparent background, but still some white in antialiased pixels.

That's right - thanks.

Otfried