[cairo] Using the span renderer to push spans to an FPGA?

Jeff Muizelaar jeff at infidigm.net
Sat Jun 13 16:21:04 PDT 2009

On Sat, Jun 13, 2009 at 11:04:50PM +0200, Leon Woestenberg wrote:
> Hello Jeff,
> On Thu, Jun 4, 2009 at 9:53 PM, Jeff Muizelaar<jeff at infidigm.net> wrote:
> > On Wed, Jun 03, 2009 at 11:58:01PM +0200, Leon Woestenberg wrote:
> >> my current cairo backend is the image backend, which copies images
> >> line-by-line to an FPGA for display.
> >>
> >> As we have control over the FPGA, I wondered if the span renderer be
> >> exploited to send spans to the FPGA, instead of the raw image data?
> >
> > This would certainly be possible. The following tree draws spans directly using gl.
> > http://cgit.freedesktop.org/~anholt/cairo/log/?h=gl-span-renderer
> >
> Thanks for the pointer.
> I had already been looking at this tree, but I could not find at what
> point in the code the spans can be handed off to a device for
> rendering.
> Could you give me an additional, more fine grained, pointer?

_cairo_gl_surface_span_renderer_render_row() accumulates the spans for
the row().

and _cairo_gl_surface_span_renderer_finish() flushes them out to the
hardware by calling _cairo_gl_span_renderer_flush()

> How did this tree branch off? You started with the image back-end and
> then adapted it?

I didn't write this backend, but yes I believe the image back-end was
the starting place and it was adapted from there.


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