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Multivar colorbar #31214

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cbda376
Initial bivar_colorbar
trygvrad Feb 27, 2026
84860f6
initial multivar colorbar
trygvrad Mar 8, 2026
29b7796
working on constrained_layout
trygvrad Apr 13, 2026
65db055
tests for colorbar_multivar
trygvrad Apr 22, 2026
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4 changes: 4 additions & 0 deletions doc/api/figure_api.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,8 @@ Annotating
:nosignatures:

Figure.colorbar
Figure.colorbar_bivar
Figure.colorbar_multivar
Figure.legend
Figure.text
Figure.suptitle
Expand Down Expand Up @@ -254,6 +256,8 @@ Annotating
:nosignatures:

SubFigure.colorbar
SubFigure.colorbar_bivar
SubFigure.colorbar_multivar
SubFigure.legend
SubFigure.text
SubFigure.suptitle
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2 changes: 2 additions & 0 deletions doc/api/pyplot_summary.rst
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Expand Up @@ -263,6 +263,8 @@ Colormapping

clim
colorbar
colorbar_bivar
colorbar_multivar
gci
sci
get_cmap
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63 changes: 46 additions & 17 deletions lib/matplotlib/_constrained_layout.py
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Expand Up @@ -398,12 +398,18 @@ def make_layout_margins(layoutgrids, fig, renderer, *, w_pad=0, h_pad=0,
# make margin for colorbars. These margins go in the
# padding margin, versus the margin for Axes decorators.
for cbax in ax._colorbars:
if cbax._colorbar_info["type"] == "MultivarColorbar":
# a matplotlib.colorbar.MultivarColorbar object
fig = cbax.axes[0].get_figure(root=False)
tightbbox = cbax.get_tightbbox(renderer, for_layout_only=True)
cbbbox = tightbbox.transformed(fig.transFigure.inverted())
else:
cbpos, cbbbox = get_pos_and_bbox(cbax, renderer)
# note pad is a fraction of the parent width...
pad = colorbar_get_pad(layoutgrids, cbax)
# colorbars can be child of more than one subplot spec:
cbp_rspan, cbp_cspan = get_cb_parent_spans(cbax)
loc = cbax._colorbar_info['location']
cbpos, cbbbox = get_pos_and_bbox(cbax, renderer)
if loc == 'right':
if cbp_cspan.stop == ss.colspan.stop:
# only increase if the colorbar is on the right edge
Expand Down Expand Up @@ -691,7 +697,7 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None, compress=Fa
Parameters
----------
layoutgrids : dict
cbax : `~matplotlib.axes.Axes`
cbax : `~matplotlib.colorbar.MultiColorbars` or `~matplotlib.axes.Axes`
Axes for the colorbar.
renderer : `~matplotlib.backend_bases.RendererBase` subclass.
The renderer to use.
Expand All @@ -701,22 +707,30 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None, compress=Fa
compress : bool
Whether we're in compressed layout mode.
"""
cb_info = cbax._colorbar_info
if cb_info["type"] == "MultivarColorbar":
multi_cbar = cbax
cbaxes = multi_cbar.axes
multi = True
else:
multi = False
cbaxes = [cbax]

parents = cbax._colorbar_info['parents']
parents = cb_info['parents']
gs = parents[0].get_gridspec()
fig = cbax.get_figure(root=False)
fig = cbaxes[0].get_figure(root=False)
trans_fig_to_subfig = fig.transFigure - fig.transSubfigure

cb_rspans, cb_cspans = get_cb_parent_spans(cbax)
bboxparent = layoutgrids[gs].get_bbox_for_cb(rows=cb_rspans,
cols=cb_cspans)
pb = layoutgrids[gs].get_inner_bbox(rows=cb_rspans, cols=cb_cspans)

location = cbax._colorbar_info['location']
anchor = cbax._colorbar_info['anchor']
fraction = cbax._colorbar_info['fraction']
aspect = cbax._colorbar_info['aspect']
shrink = cbax._colorbar_info['shrink']
location = cb_info['location']
anchor = cb_info['anchor']
fraction = cb_info['fraction']
aspect = cb_info['aspect']
shrink = cb_info['shrink']

# For colorbars with a single parent in compressed layout,
# use the actual visual size of the parent axis after apply_aspect()
Expand All @@ -736,14 +750,20 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None, compress=Fa
# Keep the pb x-coordinates but use actual y-coordinates
pb = Bbox.from_extents(pb.x0, actual_pos_fig.y0,
pb.x1, actual_pos_fig.y1)
elif location in ('top', 'bottom'):
else: # location in ('top', 'bottom'):
# For horizontal colorbars, use the actual parent bbox width
# for colorbar sizing
# Keep the pb y-coordinates but use actual x-coordinates
pb = Bbox.from_extents(actual_pos_fig.x0, pb.y0,
actual_pos_fig.x1, pb.y1)

cbpos, cbbbox = get_pos_and_bbox(cbax, renderer)
if multi:
tightbbox = martist._get_tightbbox_for_layout_only(multi_cbar, renderer)
cbbbox = tightbbox.transformed(fig.transFigure.inverted())
cbpos = multi_cbar._get_original_position()
cbpos = cbpos.transformed(fig.transSubfigure - fig.transFigure)
else:
cbpos, cbbbox = get_pos_and_bbox(cbax, renderer)

# Colorbar gets put at extreme edge of outer bbox of the subplotspec
# It needs to be moved in by: 1) a pad 2) its "margin" 3) by
Expand All @@ -754,6 +774,8 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None, compress=Fa
pbcb = pb.shrunk(fraction, shrink).anchored(anchor, pb)
# The colorbar is at the left side of the parent. Need
# to translate to right (or left)
if multi:
pbcb.x1 = pbcb.x0 + cbbbox.width
if location == 'right':
lmargin = cbpos.x0 - cbbbox.x0
dx = bboxparent.x1 - pbcb.x0 + offset['right']
Expand All @@ -768,6 +790,8 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None, compress=Fa
pbcb = pbcb.translated(dx, 0)
else: # horizontal axes:
pbcb = pb.shrunk(shrink, fraction).anchored(anchor, pb)
if multi:
pbcb.y1 = pbcb.y0 + cbbbox.height
if location == 'top':
bmargin = cbpos.y0 - cbbbox.y0
dy = bboxparent.y1 - pbcb.y0 + offset['top']
Expand All @@ -781,14 +805,19 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None, compress=Fa
offset['bottom'] += cbbbox.height + cbpad
pbcb = pbcb.translated(0, dy)

pbcb = trans_fig_to_subfig.transform_bbox(pbcb)
cbax.set_transform(fig.transSubfigure)
cbax._set_position(pbcb)
cbax.set_anchor(anchor)
if location in ['bottom', 'top']:
aspect = 1 / aspect
cbax.set_box_aspect(aspect)
cbax.set_aspect('auto')
if multi:
new_bboxs = multi_cbar._get_tight_packing_inside(pbcb)
else:
new_bboxs = [pbcb]
for cbax, new_bbox in zip(cbaxes, new_bboxs):
transformed_bbox = trans_fig_to_subfig.transform_bbox(new_bbox)
cbax.set_transform(fig.transSubfigure)
cbax._set_position(transformed_bbox)
cbax.set_anchor(anchor)
cbax.set_box_aspect(aspect)
cbax.set_aspect('auto')
return offset


Expand Down
3 changes: 2 additions & 1 deletion lib/matplotlib/backend_bases.py
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Expand Up @@ -3275,7 +3275,8 @@ def press_zoom(self, event):
# to the edge of the Axes bbox in the other dimension. To do that we
# store the orientation of the colorbar for later.
parent_ax = axes[0]
if hasattr(parent_ax, "_colorbar"):
if hasattr(parent_ax, "_colorbar") and hasattr(parent_ax._colorbar,
"orientation"):
cbar = parent_ax._colorbar.orientation
else:
cbar = None
Expand Down
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