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Exporting concise SVG by melwyncarlo · Pull Request #30598 · matplotlib/matplotlib · GitHub

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Exporting concise SVG #30598

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f36876c
Issue 17424 Preliminary Solution
melwyncarlo Sep 25, 2025
3b86436
Merge branch 'matplotlib:main' into issue_17424
melwyncarlo Sep 25, 2025
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4 changes: 4 additions & 0 deletions lib/matplotlib/backends/backend_mixed.py
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,10 @@ def __getattr__(self, attr):
# to the underlying C implementation).
return getattr(self._renderer, attr)

def is_svg_renderer(self):
from matplotlib.backends.backend_svg import RendererSVG
return isinstance(self._renderer, RendererSVG)

def start_rasterizing(self):
"""
Enter "raster" mode. All subsequent drawing commands (until
Expand Down
206 changes: 203 additions & 3 deletions lib/matplotlib/backends/backend_svg.py
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Expand Up @@ -590,12 +590,18 @@ def _get_style_dict(self, gc, rgbFace):
attrib['stroke'] = rgb2hex(rgb)
if not forced_alpha and rgb[3] != 1.0:
attrib['stroke-opacity'] = _short_float_fmt(rgb[3])
if linewidth != 1.0:
attrib['stroke-width'] = _short_float_fmt(linewidth)
# Reference: https://www.w3.org/TR/SVG11/coords.html#Units
# The below formula, apart from linewidth, can be stored
# pre-calculated.
attrib['stroke-width'] = _short_float_fmt(
linewidth * 100.0 * np.sqrt(2) / \
np.sqrt(self.width*self.width+self.height*self.height)
) + '%'
if gc.get_joinstyle() != 'round':
attrib['stroke-linejoin'] = gc.get_joinstyle()
if gc.get_capstyle() != 'butt':
attrib['stroke-linecap'] = _capstyle_d[gc.get_capstyle()]
attrib['vector-effect'] = 'non-scaling-stroke'

return attrib

Expand Down Expand Up @@ -664,6 +670,201 @@ def option_image_nocomposite(self):
# docstring inherited
return not mpl.rcParams['image.composite_image']

def _draw_shape_prefix(self, gc):
if gc.get_url() is not None:
self.writer.start('a', {'xlink:href': gc.get_url()})
clip_attrs = self._get_clip_attrs(gc)
if clip_attrs:
self.writer.start('g', **clip_attrs)
return True
return False

def _draw_shape_content(self, tag, gc, baseTransform, rgbFace, **kwargs):
def to_svg_string(transform_matrix):
return ('matrix('
f'{transform_matrix[0, 0]}, {transform_matrix[1, 0]}, '
f'{transform_matrix[0, 1]}, {transform_matrix[1, 1]}, '
f'{transform_matrix[0, 2]}, {transform_matrix[1, 2]}'
')')
# Option-1: (preferred alternative; currently in use over here)
# Set attrib['vector-effects'] = 'non-scaling-stroke'
# in _get_style_dict()
# Issue:
# Part of SVG Tiny 1.2 and SVG 2 (active development)
# Supported on modern browsers but not all image editors
# Does not scale stroke-width on scaling/zooming,
# though it zooms well on browsers while viewing.
# Does not directly scale stroke-width when exporting to
# higher resolution raster images (PNG); requires first
# manually scaling the SVG by:
# 1. scaling the SVG width, height, and viewbox
# e.g.: current width = 480.0, height = 345.6
# viewbox = 0 0 480.0 345.6
# To obtain 4800px x 3456px image, set
# new width = 4800.0, height = 3456.0
# viewbox = 0 0 4800.0 3456.0
# 2. Applying transform scale() to the figure
# e.g.: (cont'd) scale factor = 4800 / 480 = 10
# so, change: <g id="figure_1"> to:
# <g id="figure_1" transform="scale(10)">
# Option-2:
# gc.set_linewidth(gc.get_linewidth() / transform_scale_factor)
# Issue:
# Works well if tranform_matrix consists only of
# uniform scaling and translation, i.e.,
# transform_scale_factor = abs(transform_matrix[0, 0])
# Otherwise, it requires an advanced affine matrix
# decomposition algorithm (SVD or Polar) to compute the
# transform_scale_factor.
# Still does not correct non-uniform stroke-width
# caused by shearing/skewing.
# Option-3: (currently in use in main branch)
# Convert all shapes to path, apply transformations to path,
# and then draw path. This basically avoids all the above
# mentioned pitfalls.
trans_and_flip_matrix =\
self._make_flip_transform(baseTransform).get_matrix()
transmat_string = to_svg_string(trans_and_flip_matrix)
kwargs['transform'] = (transmat_string + ' ' + kwargs['transform']) if\
'transform' in kwargs else transmat_string
kwargs['style'] = self._get_style(gc, rgbFace)
self.writer.element(tag, **kwargs)

def _draw_shape_suffix(self, gc, clip_attrs_exist):
if clip_attrs_exist:
self.writer.end('g')
if gc.get_url() is not None:
self.writer.end('a')

def _draw_shape(self, tag, gc, baseTransform, rgbFace, **kwargs):
clip_attrs_exist = self._draw_shape_prefix(gc)
self._draw_shape_content(tag, gc, baseTransform, rgbFace, **kwargs)
self._draw_shape_suffix(gc, clip_attrs_exist)

def draw_ellipse(self, gc, baseTransform, rgbFace, cxy, semi_major,
semi_minor, angle):
self._draw_shape('ellipse', gc, baseTransform, rgbFace, cx=str(cxy[0]),
cy=str(cxy[1]), rx=str(semi_major), ry=str(semi_minor),
transform=(f'rotate({angle}, {cxy[0]}, {cxy[1]})' if\
angle else ''))

def draw_circle(self, gc, baseTransform, rgbFace, cxy, radius):
self._draw_shape('circle', gc, baseTransform, rgbFace,
cx=str(cxy[0]), cy=str(cxy[1]), r=str(radius))

def draw_annulus(self, gc, baseTransform, rgbFace, cxy,
semi_major_outer, semi_minor_outer, width, angle):
clip_attrs_exist = self._draw_shape_prefix(gc)
self.writer.start('defs')
outer_shape_id = self._make_id('', '')
if semi_major_outer == semi_minor_outer:
self.writer.element('circle', id=outer_shape_id, cx=str(cxy[0]),
cy=str(cxy[1]), r=str(semi_major_outer))
else:
self.writer.element('ellipse', id=outer_shape_id, cx=str(cxy[0]),
cy=str(cxy[1]), rx=str(semi_major_outer),
ry=str(semi_minor_outer))
mask_id = self._make_id('', '')
self.writer.start('mask', {'id': mask_id})
self.writer.element('use', href=f'#{outer_shape_id}', fill='white')
semi_major_inner = semi_major_outer - width
if semi_major_outer == semi_minor_outer:
self.writer.element('circle', cx=str(cxy[0]), cy=str(cxy[1]),
r=str(semi_major_inner), fill='black')
else:
semi_minor_inner = semi_minor_outer - width
self.writer.element('ellipse', id=outer_shape_id, cx=str(cxy[0]),
cy=str(cxy[1]), rx=str(semi_major_inner),
ry=str(semi_minor_inner))
self.writer.end('mask')
self.writer.end('defs')
self._draw_shape_content('use', gc, baseTransform, rgbFace,
href=f'#{outer_shape_id}', mask=f'url(#{mask_id})',
transform=(f'rotate({angle}, {cxy[0]}, {cxy[1]})' if\
angle else ''))
self._draw_shape_suffix(gc, clip_attrs_exist)

def _get_arc_data(self, cxy, semi_major, semi_minor,
angle, theta1, theta2):
# Reference: https://www.w3.org/TR/SVG/implnote.html#ArcImplementationNotes
delta_theta = theta2 - theta1
angle = np.radians(angle)
theta1 = np.radians(theta1)
theta2 = np.radians(theta2)
sin_phi = np.sin(angle)
cos_phi = np.cos(angle)
sin_theta1 = np.sin(theta1)
cos_theta1 = np.cos(theta1)
sin_theta2 = np.sin(theta2)
cos_theta2 = np.cos(theta2)
rx_cos_theta1 = semi_major * cos_theta1
ry_sin_theta1 = semi_minor * sin_theta1
rx_cos_theta2 = semi_major * cos_theta2
ry_sin_theta2 = semi_minor * sin_theta2
x1 = cos_phi*rx_cos_theta1 - sin_phi*ry_sin_theta1 + cxy[0]
y1 = sin_phi*rx_cos_theta1 + cos_phi*ry_sin_theta1 + cxy[1]
x2 = cos_phi*rx_cos_theta2 - sin_phi*ry_sin_theta2 + cxy[0]
y2 = sin_phi*rx_cos_theta2 + cos_phi*ry_sin_theta2 + cxy[1]
fA = 1 if abs(delta_theta) > 180 else 0
fS = 1 if delta_theta > 0 else 0
return (x1, y1), (x2, y2), fA, fS

def draw_arc(self, gc, baseTransform, rgbFace, cxy, semi_major, semi_minor,
angle, theta1, theta2):
xy1, xy2, fA, fS = self._get_arc_data(cxy, semi_major, semi_minor,
angle, theta1, theta2)
arc_path_data = f'M {xy1[0]} {xy1[1]} A {semi_major} {semi_minor} '\
f'{angle} {fA} {fS} {xy2[0]} {xy2[1]}'
self._draw_shape('path', gc, baseTransform, rgbFace, d=arc_path_data)

def draw_rectangle(self, gc, baseTransform, rgbFace, xy, cxy,
width, height, angle, rotation_point):
self._draw_shape('rect', gc, baseTransform, rgbFace,
x=str(xy[0]), y=str(xy[1]), width=str(width), height=str(height),
transform=(f'rotate({angle}, {rotation_point[0]}, '\
f'{rotation_point[1]})' if angle else ''))

def draw_wedge(self, gc, baseTransform, rgbFace, cxy, outer_radius,
theta1, theta2, width):
xy1_outer, xy2_outer, fA_outer, fS_outer = self._get_arc_data(
cxy, outer_radius, outer_radius, 0, theta2, theta1
)
if width:
inner_radius = outer_radius - width
xy1_inner, xy2_inner, fA_inner, fS_inner = self._get_arc_data(
cxy, inner_radius, inner_radius, 0, theta1, theta2
)
wedge_path_data = f'M {xy1_inner[0]} {xy1_inner[1]} '\
f'A {inner_radius} {inner_radius} 0 {fA_inner} {fS_inner} '\
f'{xy2_inner[0]} {xy2_inner[1]} '\
f'L {xy1_outer[0]} {xy1_outer[1]} '\
f'A {outer_radius} {outer_radius} 0 {fA_outer} {fS_outer} '\
f'{xy2_outer[0]} {xy2_outer[1]} z'
else:
wedge_path_data = f'M {cxy[0]} {cxy[1]} '\
f'L {xy1_outer[0]} {xy1_outer[1]} '\
f'A {outer_radius} {outer_radius} 0 {fA_outer} {fS_outer} '\
f'{xy2_outer[0]} {xy2_outer[1]} z'
self._draw_shape('path', gc, baseTransform, rgbFace, d=wedge_path_data)

def draw_polygon(self, gc, path, transform, rgbFace=None):
points_data = ' '.join(','.join(row.astype(str))\
for row in path.vertices)
self._draw_shape('polygon', gc, transform, rgbFace,
points=points_data)

def draw_polyline(self, gc, path, transform, rgbFace=None):
points_data = ' '.join(','.join(row.astype(str))\
for row in path.vertices)
self._draw_shape('polyline', gc, transform, rgbFace,
points=points_data)

def draw_steppatch(self, gc, isclosed, path, transform, rgbFace=None):
if isclosed:
self.draw_polygon(gc, path, transform, rgbFace)
else:
self.draw_polyline(gc, path, transform, rgbFace)

def _convert_path(self, path, transform=None, clip=None, simplify=None,
sketch=None):
if clip:
Expand All @@ -682,7 +883,6 @@ def draw_path(self, gc, path, transform, rgbFace=None):
path_data = self._convert_path(
path, trans_and_flip, clip=clip, simplify=simplify,
sketch=gc.get_sketch_params())

if gc.get_url() is not None:
self.writer.start('a', {'xlink:href': gc.get_url()})
self.writer.element('path', d=path_data, **self._get_clip_attrs(gc),
Expand Down
80 changes: 72 additions & 8 deletions lib/matplotlib/patches.py
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Original file line number Diff line number Diff line change
Expand Up @@ -648,7 +648,67 @@
renderer = PathEffectRenderer(self.get_path_effects(), renderer)

for draw_path_args in draw_path_args_list:
renderer.draw_path(gc, *draw_path_args)
draw_path_instead = False
# Below two lines are only for testing/comparing
# and can be removed
with open('pure_svg_mode', 'r') as f:

tacaswell Sep 25, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

If we were to merge this, we would have to provide an rcparam to control it (like we do with text in vector backends that let you pick "text + embed the fonts / hope they are available in the viewer" vs "draw text as paths")

melwyncarlo Sep 25, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

with open('pure_svg_mode', 'r') as f: is NOT for merging (release version). It's simply there to perform my comparison tests as mentioned in my Test Code Repository (link in issue description), i.e., to compare between the old method and the new method. It will be deleted.
if f.read() == '1':
from matplotlib.backends.backend_mixed import MixedModeRenderer
if isinstance(renderer, MixedModeRenderer) and renderer.is_svg_renderer():

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message:"Line too long (94 > 88)"  location:{path:"/home/runner/work/matplotlib/matplotlib/lib/matplotlib/patches.py"  range:{start:{line:657  column:89}  end:{line:657  column:95}}}  severity:WARNING  source:{name:"ruff"  url:"https://docs.astral.sh/ruff"}  code:{value:"E501"  url:"https://docs.astral.sh/ruff/rules/line-too-long"}

tacaswell Sep 25, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Rather than pin to the svg renderer, if we are going to do this then we should duck-type and allow backends to opt-in to providing more specialized rendering calls.

melwyncarlo Sep 25, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I agree, something to work on.
patch = self
base_transform = artist.Artist.get_transform(patch).get_affine()
if isinstance(patch, Shadow):
# base_transform += patch._shadow_transform
# is incorrect as order matters over here.
base_transform = patch._shadow_transform + base_transform
patch = patch.patch
common_args = (gc,
base_transform,
draw_path_args[2]) # rgbFace
if isinstance(patch, (Polygon, RegularPolygon,

tacaswell Sep 25, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I believe that we now have a high enough minimum python we can use the match statement.

melwyncarlo Sep 25, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Oh yes, I will make that change.
I was also wondering if instead of multiple conditions in this draw function, shouldn't they be called from within their respective classes itself? Or is this the right way forward?
CirclePolygon, Arrow, FancyArrow)
):
renderer.draw_polygon(gc, *draw_path_args)
elif isinstance(patch, Circle):
renderer.draw_circle(*common_args,
patch.get_center(), patch.get_radius())
elif isinstance(patch, Arc):
renderer.draw_arc(*common_args, patch.get_center(),
patch.get_width()/2, patch.get_height()/2,
patch.get_angle(), patch.theta1, patch.theta2)
elif isinstance(patch, Ellipse):
renderer.draw_ellipse(*common_args,
patch.get_center(), patch.get_width()/2,
patch.get_height()/2, patch.get_angle())
elif isinstance(patch, Annulus):
renderer.draw_annulus(*common_args,
patch.get_center(), *patch.get_radii(),
patch.get_width(), patch.get_angle())
elif isinstance(patch, Rectangle):
renderer.draw_rectangle(*common_args,
patch.get_xy(), patch.get_center(),
patch.get_width(), patch.get_height(),
patch.get_angle(),
patch._get_computed_rotation_point())
elif isinstance(patch, Wedge):
renderer.draw_wedge(*common_args,
patch.center, patch.r, patch.theta1,
patch.theta2, patch.width)
elif isinstance(patch, StepPatch):
renderer.draw_steppatch(gc,
self.fill or (self._baseline is not None and \
self._baseline.ndim == 1),
*draw_path_args)
else:
draw_path_instead = True
else:
draw_path_instead = True
# Below two lines are only for testing/comparing
# and can be removed
else:
draw_path_instead = True
if draw_path_instead:
renderer.draw_path(gc, *draw_path_args)

gc.restore()
renderer.close_group('patch')
Expand Down Expand Up @@ -827,13 +887,7 @@
# important to call the accessor method and not directly access the
# transformation member variable.
bbox = self.get_bbox()
if self.rotation_point == 'center':
width, height = bbox.x1 - bbox.x0, bbox.y1 - bbox.y0
rotation_point = bbox.x0 + width / 2., bbox.y0 + height / 2.
elif self.rotation_point == 'xy':
rotation_point = bbox.x0, bbox.y0
else:
rotation_point = self.rotation_point
rotation_point = self._get_computed_rotation_point()
return transforms.BboxTransformTo(bbox) \
+ transforms.Affine2D() \
.translate(-rotation_point[0], -rotation_point[1]) \
Expand All @@ -842,6 +896,16 @@
.scale(1, 1 / self._aspect_ratio_correction) \
.translate(*rotation_point)

def _get_computed_rotation_point(self):
bbox = self.get_bbox()
if self.rotation_point == 'center':
width, height = bbox.x1 - bbox.x0, bbox.y1 - bbox.y0
return bbox.x0 + width / 2., bbox.y0 + height / 2.
elif self.rotation_point == 'xy':
return bbox.x0, bbox.y0
else:
return self.rotation_point

@property
def rotation_point(self):
"""The rotation point of the patch."""
Expand Down
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