[cairo] Drawing into a memory block

[Jonathan Roewen]

> That's the right function to tell cairo to draw to a memory buffer
> based at gfx_info->video_base. One significant issue is whether your
> framebuffer supports an image format compatible with one of the
> cairo_format_t values.
> 
> Are you not seeing any data being written to the buffer you pass in to
> this function? You should be.

Even if the data format is incorrect, I should get some graphical
garbage, but it's just completely black. And I wondered about the
format thing, so I made a loop to draw correctly (which I know works).

I had to modify cairo sources so I could build without font support.
Only two files: cairo_gstate.c, line 2287, and cairo-font.c... I just
set the pointer to NULL, but still returned CAIRO_STATUS_SUCCESS.
Perhaps I might need to create a dummy font-engine that just ignores
everything?

At the moment, I don't have enough of a base to support font-config,
which is why I don't have font support, but is that why it won't draw?
The render loop does finish... so I suspect the code should've died
before then otherwise.

Jonathan