Avoid the overhead of sorting the rectangle in
_cairo_traps_tessellate_convex_quad() by constructing the trap directly
from the line segment. This also has secondary effects in only passing
the non-degenerate trap to _cairo_traps_add_trap().
For rectilinear Hilbert curves this makes the rectilinear stoker over 4x
faster.
The rectilinear stroke finalized the cairo_traps_t passed to it - which
was then subsequently used without re-initialized. So instead of
finalizing the structure, just remove any traps that we may have added
(leaving the limits and memory intact).
These two functions were hiding away some important details
about strictness of inequalities. Also, the callers differ
on the strictness they need. Everything is cleaner and more
flexible by making the callers just call _cairo_slope_compare
directly.
The optimization to avoid sqrt() for horizontal/vertical lines in
_compute_normalized_device_slope was causing us to return a negative
magnitude with a positive slope for left-to-right and bottom-to-top
lines, instead of always returning a positive magnitude and a slope
with an appropriate sign.
The original test for wild miters would only work with a square transform
(and, in fact, the original code required an identity transform). Instead of
fixing that, I replaced it with a more obvious test which makes sure the
miter corner lies between the two faces and not out in space somewhere.
This fixes the current failure get-path-extents, which is a
demonstration of the following bug:
cairo_stroke_extents() gives wrong result for arcs in some cases
https://bugs.freedesktop.org/show_bug.cgi?id=7245
Many thanks to Michael Urman whose review of early versions of
this work found a fatal mistake in my algebra.
Every time we assign or return a hard-coded error status wrap that value
with a call to _cairo_error(). So the idiom becomes:
status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
or
return _cairo_error (CAIRO_STATUS_INVALID_DASH);
This ensures that a breakpoint placed on _cairo_error() will trigger
immediately cairo detects the error.
Now, the functions to add new data to a polygon all become void,
and there's a new _cairo_polygon_status call to query the status
at the end of a sequence of operations.
With this change, we fix many callerswhich were previously not
checking the return values of _cairo_polygon functions by adding
only a single call to _cairo_polygon_status rathern than several
new checks.
Adds some state, 'dash_starts_on', to keep track of whether a dashed path
starts with dash_on or not. This fixes the 'leaky-dash' bug (#4863) and
some other degenerate cases. The new version is, in my opinion,
considerably cleaner and more understandable than the old code.
Finally, the rewrite changes the behaviour of dashing to add degenerate
caps around corners that start at the same place as a dash begins. This
matches the behaviour seen in acroread.
This rewrite is based on an initial rewrite done by Jeff Smith.
has_initial_sub_path more accurately describes the condition we want to
track. This flag is used to indicate when an initial sub_path needs capping
but has no associated slope and thus no associated faces.
This custom stroking code allows backends to use optimized region-based
drawing operations for rectilinear strokes. This results in a 5-25x
performance improvement when drawing rectilinear shapes:
image-rgb box-outline-stroke-100 0.18 -> 0.01: 25.58x speedup
████████████████████████▋
image-rgba box-outline-stroke-100 0.18 -> 0.01: 25.57x speedup
████████████████████████▋
xlib-rgb box-outline-stroke-100 0.49 -> 0.06: 8.67x speedup
███████▋
xlib-rgba box-outline-stroke-100 0.22 -> 0.04: 5.39x speedup
████▍
In other words, using cairo_stroke instead of cairo_fill to draw the
same shape was 5-15x slower before, but is 1.2-2x faster now.
This follows the PDF and SVG specifications which only draw degenerate paths when
round caps are in effect.
With this commit, the degenerate-path test passes with the image, xlib, and pdf
backends, (but still fails with ps and svg backends).
This patch was produced with the following (GNU) sed script:
sed -i -r -e '/^[ \t]*\/?\*/ s/[ \t]+$//'
run on all *.[ch] files within cairo, (though I manually excluded
src/cairo-atsui-font.c which has a code line that appears as a comment
to this script).
