[cairo] Wayland remote rendering: Cairo/Pango as Remote Calls over VNC

Øyvind Kolås pippin at gimp.org
Tue Aug 24 17:01:15 UTC 2021

On Mon, Aug 23, 2021 at 2:20 PM Rick van Rein <rick at openfortress.nl> wrote:
> This gave me the idea that remote procedure calls for Cairo/Pango
> APIs could support remote Wayland.  VNC may be designed for pixels,
> but it is open to extensions and an RPC protocol could be added as
> a pseudo-encoding for pixels.

I am working on and exerpimented with a project that among many other
things is such a remote graphics protocol and renderer:


it is a ANSI standard terminal extended with modern a modern vector
graphics protocol, similar to how terminals used to be graphical with
regis/tektronix graphics. To me it is natural that it is possible to
upgrade a terminal from text mode to graphics mode, just like one can
upgrade the console of ones workstation from text mode to graphics
mode. By using this terminal emulator directly on the framebuffer
device; one gets the potential foundation of a multi-tasking desktop
that uses significantly less RAM than GPU based compositing window
managers allocating a texture per window (the model does support
texture caching of clients - for now the caching happens for sub
regions of the desktop across clients).

All the post script derived imaging models of
direct2d/quartz/pdf/cairo/html canvas are closely related, ctx aligns
more closely with HTML5 Canvas 2D context than cairo; though it is
inspired by both. Ctx also sports features like CMYK, floating point
raster images and ICC color management on top of the base rendering
capabilities.  See https://ctx.graphics/protocol/ for the actual
protocol itself. In ctx' implementation read-back of graphics state is
done locally instead of incurring round trips; if one ignores ability
to read back graphics state really minimal minimal bindings are
possible like this ctx implementation for bash:

Textures are transmitted in-band, this even works for low resolution
video playback locally - but using a different transport or doing
shared memory out-of-band when renderer and client are on the same
machine similar to how the kitty terminal graphics protocol works will
be desired or neccesary.

ctx is fast compared with cairo; especially considering that the only
SIMD support in ctx is from what memcpy provides. In benchmarks of
source-over, source-copy permuted with color, linear, radial, nearest
neighbour and bilinear patterns, the only cases where cairo/pixman is
faster than ctx is for bilinear patterns, for all the other cases the
combination of the faster (sometimes even more accurate) rasterizer
and optimized portable C code of ctx wins. For the most common paint
source, color fills, ctx is currently 1.8-3x faster than cairo, for
gradients fills ctx is sometimes 10x faster.


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