[cairo] Writing Surface to PNG based on Window Context: POSSIBLE?

[Gerdus van Zyl]

Well it works for me! Below is the code I use:
tsurf = ctx.get_target()
tsurf.write_to_png("screenshot.png")

This is code that works on MS Windows. According to the API docs it
should work for any pixel based surface. But as suggested if you
structure your code to be able to render to any cairo context that
would of course be better in the long term.

~Gerdus

On Sat, Mar 21, 2009 at 3:22 AM, Neil Mayhew
<neil_mayhew at users.sourceforge.net> wrote:
> On 20/03/09 04:31 PM darethehair wrote:
>> How does one invoke the 'write_to_png' in that situation? The reason I
>> ask this is that I would like to be able to draw on the 'screen', but
>> also re-direct to a PNG (or whatever) file if I want to.
>
> You can't write a window to a PNG (not with cairo, anyway). However, you
> can refactor your program into two parts: one that takes a cairo.Context
> as a parameter and generates the desired graphics, and another one that
> sets up the destination surface and context and calls the other
> (drawing) part.
>
> I've done this for one program I have been writing. It uses gtkmm and
> cairomm rather than PyCairo, but the principle is the same. Depending on
> the command-line arguments it either opens up a window and hooks the
> pure-cairo drawing function to the expose event, or it creates a
> pure-cairo surface, calls the drawing function on that, and then writes
> it out. However, you could instead have a File -> Export menu item that
> does the same thing.
>
> In case it's helpful, I've included the code I am using. It's in C++,
> but hopefully you can translate.
>
> --Neil
>
> void export(std::string filename, int size_x, int size_y)
> {
>    std::string suffix = filename.substr(filename.rfind('.') + 1);
>
>    Cairo::RefPtr<Cairo::Surface> surface;
>
>    if (suffix == "pdf")
>        surface = Cairo::PdfSurface::create(filename, size_x, size_y);
>    else if (suffix == "svg")
>        surface = Cairo::SvgSurface::create(filename, size_x, size_y);
>    else if (suffix == "ps")
>        surface = Cairo::PsSurface::create(filename, size_x, size_y);
>    else if (suffix == "png")
>        surface = Cairo::ImageSurface::create(Cairo::FORMAT_RGB24, \
>            size_x, size_y);
>    else
>        throw std::runtime_error("Unknown filename suffix");
>
>    Cairo::RefPtr<Cairo::Context> context = \
>        Cairo::Context::create(surface);
>
>    if (suffix == "png")
>    {
>        context->set_source_rgb(1.0, 1.0, 1.0);
>        context->paint();
>    }
>
>    render(context, size_x, size_y);
>
>    if (suffix == "png")
>        surface->write_to_png(filename);
> }
>
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