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cairo: remove the append_path() fast path #13042

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Dec 29, 2018
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cairo: remove the append_path() fast path #13042

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101 changes: 15 additions & 86 deletions lib/matplotlib/backends/backend_cairo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -71,93 +71,22 @@ def buffer_info(self):
return (self.__data, self.__size)


# Mapping from Matplotlib Path codes to cairo path codes.
_MPL_TO_CAIRO_PATH_TYPE = np.zeros(80, dtype=int) # CLOSEPOLY = 79.
_MPL_TO_CAIRO_PATH_TYPE[Path.MOVETO] = cairo.PATH_MOVE_TO
_MPL_TO_CAIRO_PATH_TYPE[Path.LINETO] = cairo.PATH_LINE_TO
_MPL_TO_CAIRO_PATH_TYPE[Path.CURVE4] = cairo.PATH_CURVE_TO
_MPL_TO_CAIRO_PATH_TYPE[Path.CLOSEPOLY] = cairo.PATH_CLOSE_PATH
# Sizes in cairo_path_data_t of each cairo path element.
_CAIRO_PATH_TYPE_SIZES = np.zeros(4, dtype=int)
_CAIRO_PATH_TYPE_SIZES[cairo.PATH_MOVE_TO] = 2
_CAIRO_PATH_TYPE_SIZES[cairo.PATH_LINE_TO] = 2
_CAIRO_PATH_TYPE_SIZES[cairo.PATH_CURVE_TO] = 4
_CAIRO_PATH_TYPE_SIZES[cairo.PATH_CLOSE_PATH] = 1


def _append_paths_slow(ctx, paths, transforms, clip=None):
for path, transform in zip(paths, transforms):
for points, code in path.iter_segments(
transform, remove_nans=True, clip=clip):
if code == Path.MOVETO:
ctx.move_to(*points)
elif code == Path.CLOSEPOLY:
ctx.close_path()
elif code == Path.LINETO:
ctx.line_to(*points)
elif code == Path.CURVE3:
cur = np.asarray(ctx.get_current_point())
a = points[:2]
b = points[-2:]
ctx.curve_to(*(cur / 3 + a * 2 / 3), *(a * 2 / 3 + b / 3), *b)
elif code == Path.CURVE4:
ctx.curve_to(*points)


def _append_paths_fast(ctx, paths, transforms, clip=None):
# We directly convert to the internal representation used by cairo, for
# which ABI compatibility is guaranteed. The layout for each item is
# --CODE(4)-- -LENGTH(4)- ---------PAD(8)---------
# ----------X(8)---------- ----------Y(8)----------
# with the size in bytes in parentheses, and (X, Y) repeated as many times
# as there are points for the current code.
ffi = cairo.ffi

# Convert curves to segment, so that 1. we don't have to handle
# variable-sized CURVE-n codes, and 2. we don't have to implement degree
# elevation for quadratic Beziers.
cleaneds = [path.cleaned(transform, remove_nans=True, clip=clip)
for path, transform in zip(paths, transforms)]
vertices = np.concatenate([cleaned.vertices for cleaned in cleaneds])
codes = np.concatenate([cleaned.codes for cleaned in cleaneds])

# Remove unused vertices and convert to cairo codes. Note that unlike
# cairo_close_path, we do not explicitly insert an extraneous MOVE_TO after
# CLOSE_PATH, so our resulting buffer may be smaller.
vertices = vertices[(codes != Path.STOP) & (codes != Path.CLOSEPOLY)]
codes = codes[codes != Path.STOP]
codes = _MPL_TO_CAIRO_PATH_TYPE[codes]

# Where are the headers of each cairo portions?
cairo_type_sizes = _CAIRO_PATH_TYPE_SIZES[codes]
cairo_type_positions = np.insert(np.cumsum(cairo_type_sizes), 0, 0)
cairo_num_data = cairo_type_positions[-1]
cairo_type_positions = cairo_type_positions[:-1]

# Fill the buffer.
buf = np.empty(cairo_num_data * 16, np.uint8)
as_int = np.frombuffer(buf.data, np.int32)
as_int[::4][cairo_type_positions] = codes
as_int[1::4][cairo_type_positions] = cairo_type_sizes
as_float = np.frombuffer(buf.data, np.float64)
mask = np.ones_like(as_float, bool)
mask[::2][cairo_type_positions] = mask[1::2][cairo_type_positions] = False
as_float[mask] = vertices.ravel()

# Construct the cairo_path_t, and pass it to the context.
ptr = ffi.new("cairo_path_t *")
ptr.status = cairo.STATUS_SUCCESS
ptr.data = ffi.cast("cairo_path_data_t *", ffi.from_buffer(buf))
ptr.num_data = cairo_num_data
cairo.cairo.cairo_append_path(ctx._pointer, ptr)


_append_paths = (_append_paths_fast if cairo.__name__ == "cairocffi"
else _append_paths_slow)


def _append_path(ctx, path, transform, clip=None):
return _append_paths(ctx, [path], [transform], clip)
for points, code in path.iter_segments(
transform, remove_nans=True, clip=clip):
if code == Path.MOVETO:
ctx.move_to(*points)
elif code == Path.CLOSEPOLY:
ctx.close_path()
elif code == Path.LINETO:
ctx.line_to(*points)
elif code == Path.CURVE3:
cur = np.asarray(ctx.get_current_point())
a = points[:2]
b = points[-2:]
ctx.curve_to(*(cur / 3 + a * 2 / 3), *(a * 2 / 3 + b / 3), *b)
elif code == Path.CURVE4:
ctx.curve_to(*points)


class RendererCairo(RendererBase):
Expand Down