We can ensure that we always produce a clip region when possible by using
the rectilinear tessellator to convert complex, device-aligned polygons to
regions. Prior to using the tessellator, we relied on pixman's region code
which could only handle a union of rectangles.
For the frequent cases where we know in advance that we are dealing with a
rectilinear path, but can not use the simple region code, implement a
variant of the Bentley-Ottmann tessellator. The advantages here are that
edge comparison is very simple (we only have vertical edges) and there are
no intersection, though possible overlaps. The idea is the same, maintain
a y-x sorted queue of start/stop events that demarcate traps and sweep
through the active edges at each event, looking for completed traps.
The motivation for this was noticing a performance regression in
box-fill-outline with the self-intersection work:
1.9.2 to HEAD^: 3.66x slowdown
HEAD^ to HEAD: 5.38x speedup
1.9.2 to HEAD: 1.57x speedup
The cause of which was choosing to use spans instead of the region handling
code, as the complex polygon was no longer being tessellated.
The active edge list is typically short, and the skiplist adds significant
overhead that far outweigh the benefit of the O(n lg n) sort. Instead we
track the position of the last insertion edge, knowing that the start
events are lexicographically sorted, and begin a linear search from there.
We refactor the surface fallbacks to convert full strokes and fills to the
intermediate polygon representation (as opposed to before where we
returned the trapezoidal representation). This allow greater flexibility
to choose how then to rasterize the polygon. Where possible we use the
local spans rasteriser for its increased performance, but still have the
option to use the tessellator instead (for example, with the current
Render protocol which does not yet have a polygon image).
In order to accommodate this, the spans interface is tweaked to accept
whole polygons instead of a path and the tessellator is tweaked for speed.
Performance Impact
==================
...
Still measuring, expecting some severe regressions.
...
Cairo should include the contents of subwindows when using a Window as a
source but will clip to subwindows when using a Window as a destination.
This can be set using the GC's subwindow_mode.
XCopyArea and XFillRectangle can however only use one GC for both source
and destination. Cairo's mode is set to (the default) ClipByChildren.
This means that copying from a Window is broken, so we only allow the
optimization when we know that the source is a Pixmap.
The performance impact of this change has not been tested. It should be
small, as the code will use XRender otherwise.
If it turns out to be a bigger impact, the optimizations could be
improved by doing a two-step copy process:
1) Copy to an intermediate Pixmap with IncludeInferiors
2) Copy to the destination with ClipByChildren
(potentially omitting one one of the steps if source or destination are
known to be Pixmaps).
references:
commit 0c5d28a4e5https://bugs.freedesktop.org/show_bug.cgi?id=12996
Enabling 'FAST CLIP' appears to trigger an infinite loop so disable.
Enabling 'FAST FILL' has limited effect on performance, so disable whilst
the basic QT surface is improved.
Behdad pointed out that fprintf() returns a value so that we could simply
use the comma operator to return the correct value instead of the
expression-block gcc-ism.
As the associated is now explicitly the font-face used to create the font
by the user, whereas what we require is the current implementation
(quartz) font.
If a subsequent PATH_OP is just a continuation of the previous line, i.e.
it has the same gradient, then just replace the end-point of the previous
line with the new point rather than adding a new operation. Surprisingly
this occurs in the wild, but the main motivation is a future optimisation
to reduce the number of intersections during stroke-to-path.
Use hypot() instead of open-coding sqrt(x*x + y*y). In theory, the
compiler could emit highly efficient code. In practice it's slower, but
more likely to be more accurate -- but the difference over a bare sqrt()
is likely not to be perceptible.
Bug 23067 -- using clear drawing operator crashes printing
http://bugs.freedesktop.org/show_bug.cgi?id=23067
Here we were hitting an assert within the paginated surface after creating
a zero sized fallback image, due to the paginated surface being created
with an x fallback resolution of 0 dpi (by
_gtk_printer_create_cairo_surface(), gtk/gtkprinter.c:924).
Avoid the bug by guarding against bad input to
cairo_surface_set_fallback_resolution() which also allows us to identity
the invalid caller.
A problem that does not present itself whilst using spans to intermediate
masks is that the tor-span-convertor did not emit the empty rows. When
compositing directly using spans with an unbounded operator this was
causing rendering artefacts, for overlapping-glyphs and the gl backend.
Prior to introduction of the buggy members to the surface, we obviously
cannot set them. However, the boilerplate code is meant to compile against
older revisions of the library so we need to check for the existence prior
to use.
We can offload creation of gradients to server that support RENDER 0.10
and later. This greatly reduces the amount of traffic we need to send over
our display connection as the gradient patterns are much smaller than the
full image. Even if the server fallbacks to using pixman, performance
should be improved by the reduced transport overhead. Furthermore this is a
requisite to enable hardware accelerated gradients with the xlib backend.
Running cairo-perf-trace on tiny, Celeron/i915:
before: firefox-20090601 211.585
after: firefox-20090601 270.939
and on tiger, CoreDuo/nvidia:
before: firefox-20090601 70.143
after: firefox-20090601 87.326
where linear gradients are used extensively throughout the GTK+ theme.
Not quite the result I was expecting!
In particular, looking at tiny:
xlib-rgba paint-with-alpha_linear-rgba_over-512 47.11 (47.16 0.05%) -> 123.42 (123.72 0.13%): 2.62x slowdown
█▋
xlib-rgba paint-with-alpha_linear3-rgba_over-512 47.27 (47.32 0.04%) -> 123.78 (124.04 0.13%): 2.62x slowdown
█▋
xlib-rgba paint-with-alpha_linear-rgb_over-512 47.19 (47.21 0.02%) -> 123.37 (123.70 0.13%): 2.61x slowdown
█▋
xlib-rgba paint-with-alpha_linear3-rgb_over-512 47.30 (47.31 0.04%) -> 123.52 (123.62 0.09%): 2.61x slowdown
█▋
xlib-rgba paint_linear3-rgb_over-512 47.29 (47.32 0.05%) -> 118.95 (119.60 0.29%): 2.52x slowdown
█▌
xlib-rgba paint_linear-rgba_over-512 47.14 (47.17 0.06%) -> 116.76 (117.06 0.16%): 2.48x slowdown
█▌
xlib-rgba paint_linear3-rgba_over-512 47.32 (47.34 0.04%) -> 116.85 (116.98 0.05%): 2.47x slowdown
█▌
xlib-rgba paint_linear-rgb_over-512 47.15 (47.19 0.03%) -> 114.08 (114.55 0.20%): 2.42x slowdown
█▍
xlib-rgba paint-with-alpha_radial-rgb_over-512 117.25 (119.43 1.21%) -> 194.36 (194.73 0.09%): 1.66x slowdown
▋
xlib-rgba paint-with-alpha_radial-rgba_over-512 117.22 (117.26 0.02%) -> 193.81 (194.17 0.11%): 1.65x slowdown
▋
xlib-rgba paint_radial-rgba_over-512 117.23 (117.26 0.02%) -> 186.35 (186.41 0.03%): 1.59x slowdown
▋
xlib-rgba paint_radial-rgb_over-512 117.23 (117.27 0.02%) -> 184.14 (184.62 1.51%): 1.57x slowdown
▋
Before 1.10, we may choose to disable server-side gradients for the
current crop of Xorg servers, similar to the extended repeat modes.
[Updated by Chris Wilson. All bugs are his.]
The extended repeat modes were only introduced in RENDER 0.10, so disable
them if the server reports an earlier version. This is in addition to
disabling the repeat modes if we know (guess!) the server to have a buggy
implementation.
There are many common scenarios, mostly involving overlapping glyphs,
for which to guarantee correct rendering we have to composite the glyphs
via an explicit mask. That is instead of just blending the glyphs on to
the destination, we have to add the glyphs to a mask, and then composite
that mask+source with the destination.
By performing the check on whether the operator is supported prior to
acquiring the context, we do not need to handle the error part way
through the context setup. This makes the code much cleaner, and save
some work for the unsupported cases.
