When transforming the incoming paths, the goal is to transform them from
user space onto the target coordinate system. Currently for relative
paths we used user_to_device_distance as we presumed that there was no
backend scale factor. However, Alex Larsson noticed that these then
broke when playing around with such a device transform...
Reported-by: Alexander Larsson <alexl@redhat.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
This adds a new GPU accelerated backend for Cairo based on the Cogl 3D
graphics API.
This backend aims to support Cairo in a way that translates as naturally
as possible to using a GPU, it does not strive to compete with the
anti-aliasing quality of the image backend if it can't be done
efficiently using the GPU - raw performance isn't the only metric of
concern, so is power usage.
As an overview of how the backend works:
- fills are handled by tessellating paths into triangles
- the backend has an extra fill_rectangle drawing operation so we have
a fast-path for drawing rectangles which are so common.
- strokes are also tessellated into triangles.
- stroke and fill tessellations are cached to avoid the cpu overhead
of tessellation and cost of upload given that its common for apps to
re-draw the same path multiple times. The tessellations can survive
translations and rotations increasing the probability that they can be
re-used.
- sources and masks are handled using multi-texturing.
- clipping is handled with a scissor and the stencil buffer which
we're careful to only update when they really change.
- linear gradients are rendered to a 1d texture using a triangle
strip + interpolating color attributes. All cairo extend modes
are handled by corresponding texture sampler wrap modes without
needing programmable fragment processing.
- antialiasing should be handled using Cogl's multisampling API
XXX: This is a work in progress!!
TODO:
- handle at least basic radial gradients (No need to handle full
pdf semantics, since css, svg and canvas only allow radial gradients
defined as one circle + a point that must lie within the first
circle.) - currently we fall back to pixman for radial gradients.
- support glyph rendering with a decent glyph cache design. The
current plan is a per scaled-font growable cache texture + a
scratch cache for one-shot/short-lived glyphs.
- decide how to handle npot textures when lacking hardware support.
Current plan is to add a transparent border to npot textures and use
CLAMP_TO_EDGE for the default EXTEND_NONE semantics. For anything else
we can allocate a shadow npot texture and scale the original to fit
that so we can map extend modes to texture sampler modes.
Having spent the last dev cycle looking at how we could specialize the
compositors for various backends, we once again look for the
commonalities in order to reduce the duplication. In part this is
motivated by the idea that spans is a good interface for both the
existent GL backend and pixman, and so they deserve a dedicated
compositor. xcb/xlib target an identical rendering system and so they
should be using the same compositor, and it should be possible to run
that same compositor locally against pixman to generate reference tests.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
P.S. This brings massive upheaval (read breakage) I've tried delaying in
order to fix as many things as possible but now this one patch does far,
far, far too much. Apologies in advance for breaking your favourite
backend, but trust me in that the end result will be much better. :)
The brackets defined by push/pop and save/restore are independent ad
should match properly.
This means that cairo_push()-ed gstates cannot be cairo_restore()-d
and cairo_save()-d gstates cannot be cairo_pop()-ed.
Fixes group-state.
Step 1, fix the failings sighted recently by tracking clip-boxes as an
explicit property of the clipping and of composition.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
In order for custom context to automatically track when a pattern is
modify after being set on the context (and before it is used in an
operator), we need for there to be a callback when the pattern is
modified.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Allow a backend to completely reimplement the Cairo API as it wants. The
goal is to pass operations to the native backends such as Quartz,
Direct2D, Qt, Skia, OpenVG with no overhead. And to permit complete
logging contexts, and whatever else the imagination holds. Perhaps to
experiment with double-paths?
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
