A surface will have the chance to use span rendering at cairo_fill()
time by creating a renderer for a specific combination of
pattern/dst/op before the path is scan converted. The protocol is to
first call check_span_renderer() to see if the surface wants to render
with spans and then later call create_span_renderer() to create the
renderer for real once the extents of the path are known.
No backends have an implementation yet.
When computing the bounds of the clip path, we care more for a fast result
than absolute precision as the extents are only used as a guide to trim
the future operations. So computing the extents of the path suffices.
To be able to provide the extents of each operation to the backend
during the render phase the meta-surface needs to store the extents
computed by the analysis surface during the analysis phase.
The extents argument is either a pointer to the extents of the operation
stored in the meta-surface or NULL. During analysis the analysis surface
writes the extents to the meta-surface. During the render phase the extents
is made available to paginated surface backends.
Add a "cairo_rectangle_int_t *extents" argument to to the following
backend functions:
paint
mask,
stroke
fill
show_glyphs
show_text_glyphs
This will be used to pass the extents of each operation computed by
the analysis surface to the backend. This is required for implementing
EXTEND_PAD.
Only copy the pattern if we need to modify it, e.g. preserve a copy in a
snapshot or a soft-mask, or to modify the matrix. Otherwise we can
continue to use the original pattern and mark it as const in order to
generate compiler warnings if we do attempt to write to it.
Adrian Johnson discovered cases where we mistakenly compared the result
of unsigned arithmetic where we need signed quantities. Look for similar
cases in the users of cairo_rectangle_int_t.
Since there is an implicit precedence in the ranking of the analysis
return codes, provide a function to centralize the logic within the
analysis surface and isolate the backends from the complexity.
The primary bug here was some missing braces. The code was conditionally
assigning to backend_status, but then unconditionally checking for the
value assigned. The result was the leaking of an internal status value
(CAIRO_INT_STATUS_ANALYZE_META_SURFACE) which finally resulted in
an incomplete PDF file in the mask-transformed-similar test case.
While fixing this, also avoid re-using the backend_status variable so
much so that the code is more readable.
Since these functions are static we don't really need the full
name. And these two functions were both so long that they were
causing some serious line-wrap issues.
Use the utility functions _cairo_box_from_rectangle and
_cairo_box_round_to_rectangle() instead of open-coding. Simultaneously
tweak the whitespace so that all users of traps look similar.
Chris rightfully complained that having a boolean function argument is
new in cairo_show_text_glyphs, and indeed avoiding them has been one
of the API design criteria for cairo. Trying to come up with alternatives,
Owen suggested using a flag type which nicely solves the problem AND
future-proofs such a complex API.
Please welcome _flags_t APIs to cairo.h
We added cairo_has_show_text_glyphs() before. Since this is really a
surface property, should have the surface method too. Like we added
cairo_surface_show_page()...
This is needed because analysis-surface takes any UNSUPPORTED returns
as a signal for using image fallbacks. So the fallback mechanism in
_cairo_surface_show_text_glyphs() is not enough. Reported by Adrian
Johnson.
Originally reported here:
http://lists.cairographics.org/archives/cairo/2008-May/014032.html
and analyized later in the thread.
Change (font and surface) backend show_glyphs() API to take a
int *remaining_glyphs argument. It's used to communicate to the caller,
by way of setting remaining_glyphs and returning INT_STATUS_UNSUPPORTED,
that some of the glyphs were shown but not the others. The xlib backend
now correctly uses this to handle failure to upload a glyph to the server.
So the large-font test passes now.
An alternative approach could be to add some public value for glyphs
indices that are not shown. -1 perhaps (the xlib backend already uses
that value internally). Then instead of remaining_glyphs, a backend
could simply set glyph indices of glyphs shown to that -1 value.
It creates a surface that does nothing. This can be used with
cairo-analysis-surface, to compute bounds of cairo drawings without doing any
actual drawings.
If during analysis the bounding box of an operation or the number of
traps is 0, the operation is marked as natively supported. The problem
here is if the operation is unsupported by the backend, we get an
assertion when the operation is replayed during
CAIRO_PAGINATED_MODE_RENDER.
This bug was found in Inkscape when printing to the
win32_printing_surface a page that has been layed out as landscape but
landscape paper had not been selected in the print dialog.
Fix this by being careful not to mark unsupported operations as
supported during analysis even they may not be visible on the page.
I was wrong in my assertion that the call to
_cairo_path_fixed_interpret_flat() could not possibly fail with the
given _cairo_path_bounder_* callbacks - as I had missed the implicit
spline decomposition. (An interesting exercise would be to avoid the
spline allocation...) As a result we do have to check and propagate the
status return through the call stack.
The surface size and clip needs to be saved before and restored after
replaying meta surface patterns back to the analysis surface. The clip
is reset and the correct surface size is set before replaying the meta
surface.
cairo_rectangle_int16_t was being used in a number of places instead
of cairo_rectangle_int_t, which led to memory corruption when cairo was
using a fixed point format with a bigger space than 16.16 (such as 24.8).
_cairo_path_fixed_bounds can use the new _interpret_flat mechanism; this
results in tighter bounds; previously the bounds followed the control
points of the beziers, whereas now they are the bounds of the curve.
This was failing with more than one level of push/pop group. The
problem was that the meta surface replay in PS/PDF emit_meta_surface
was replaying all the meta surface commands insteads of only the
natively supported commands. The analysis surface has also been
changed to replay meta surface patterns back to the one analysis
surface instead of creating a separate analysis surface for each
pattern. The analysis surface now transforms bounding boxes with the
meta surface pattern matrix so that fallback regions are correctly
tracked.
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.
The analysis surface will calculated the tight bounding box for each
page. A new paginated-surface backend function set_bounding_box() has
been added for passing the page bounding box to the target surface at
the end of the analysis phase.
The changes to the PS file when EPS is enabled are:
- Add EPS header
- Use tight bounding box instead of page size
- Use save/restore to ensure PS interpreter is left in the same state
This reverts commit 919bea6dbb.
Sadly as Behdad points out some backends do modify the glyph array and,
for example cairo-xlib-surface, hide this from the compiler with some
evil casts.
Skip the memory duplication of the incoming glyphs if we do not need
to transform them into the backend coordinate system.
As a consequence we need to constify the glyphs passed to the backend
functions.
The analysis surface now keeps track of two regions: supported
operations, and unsupported operations. If the target surface returns
CAIRO_INT_STATUS_FLATTEN_TRANSPARENCY, the analysis surface will check
if any previous operation intersects with this operation. If there is
nothing previously drawn under the operation, the status is changed to
supported.
The meta surface has two new functions:
_cairo_meta_surface_replay_region()
_cairo_meta_surface_replay_and_create_regions()
During the analysis stage, the paginated surface replays the meta
surface using _cairo_meta_surface_replay_and_create_regions(). The
return status from each analyzed operation is saved in the meta
surface. The _cairo_meta_surface_replay_region() function allows only
operations from either the supported or unsupported region to be
replayed. This allows the paginated surface to replay only the
supported operations before emitting a fallback image for each
rectangle in the unsupported region.
