Implement bbox_inches="tight" as a post-processing step.

anntzer · anntzer · commit b16411d3d6b9 · 2021-04-09T09:53:52.000+02:00
The current implementation of bbox_inches="tight" is to no-output-draw
the figure, compute a tight bbox, and then shift all artists to their
"new" position in tight-bbox-coordinates, draw, and shift back -- which
causes all kinds of grief.

Instead, we can perform the real draw the first time, and then crop the
resulting image (either actually crop it for raster backends, or just
adjust the viewport for vector ones).

This PR is a proof-of-concept for such an approach (tests fail, that's
expected).  Currently it writes the first file to the filesystem and
then edits it; likely the first file should be just kept in memory
instead (after all the final output could also just be an im-memory
buffer).  This would also avoid having to dupe the metadata handling
(for agg).

Perhaps the method should be on the renderer instead (the exact API is
needs to be discussed).  Extra points if the API is designed in such a
way that mplcairo can directly call into it.

Currently not implemented for postscript because bbox_inches="tight"
doesn't work there anyways (although we should fix it for postscript).
Not sure about pgf output, but that's probably workable...

Final version should keep some backcompat layer, not present here to
improve readability.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2274,11 +2274,7 @@ def print_figure(
             self.figure.set_facecolor(facecolor)
             self.figure.set_edgecolor(edgecolor)
 
-            if bbox_inches is None:
-                bbox_inches = rcParams['savefig.bbox']
-
-            if (self.figure.get_constrained_layout() or
-                    bbox_inches == "tight"):
+            if self.figure.get_constrained_layout():
                 # we need to trigger a draw before printing to make sure
                 # CL works.  "tight" also needs a draw to get the right
                 # locations:
@@ -2293,22 +2289,6 @@ def print_figure(
                 with ctx:
                     self.figure.draw(renderer)
 
-            if bbox_inches:
-                if bbox_inches == "tight":
-                    bbox_inches = self.figure.get_tightbbox(
-                        renderer, bbox_extra_artists=bbox_extra_artists)
-                    if pad_inches is None:
-                        pad_inches = rcParams['savefig.pad_inches']
-                    bbox_inches = bbox_inches.padded(pad_inches)
-
-                # call adjust_bbox to save only the given area
-                restore_bbox = tight_bbox.adjust_bbox(self.figure, bbox_inches,
-                                                      canvas.fixed_dpi)
-
-                _bbox_inches_restore = (bbox_inches, restore_bbox)
-            else:
-                _bbox_inches_restore = None
-
             # we have already done CL above, so turn it off:
             cl_state = self.figure.get_constrained_layout()
             self.figure.set_constrained_layout(False)
@@ -2321,12 +2301,19 @@ def print_figure(
                         facecolor=facecolor,
                         edgecolor=edgecolor,
                         orientation=orientation,
-                        bbox_inches_restore=_bbox_inches_restore,
                         **kwargs)
+                    if bbox_inches is None:
+                        bbox_inches = rcParams["savefig.bbox"]
+                    if bbox_inches == "tight":
+                        bbox_inches = self.figure.get_tightbbox(
+                            self.figure._cachedRenderer,
+                            bbox_extra_artists=bbox_extra_artists)
+                        if pad_inches is None:
+                            pad_inches = rcParams["savefig.pad_inches"]
+                        bbox_inches = bbox_inches.padded(pad_inches)
+                    if bbox_inches:
+                        canvas.adjust_bbox(filename, bbox_inches)
             finally:
-                if bbox_inches and restore_bbox:
-                    restore_bbox()
-
                 self.figure.set_facecolor(origfacecolor)
                 self.figure.set_edgecolor(origedgecolor)
                 self.figure.set_canvas(self)
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -566,6 +566,13 @@ def print_tif(self, filename_or_obj, *, pil_kwargs=None):
 
     print_tiff = print_tif
 
+    def adjust_bbox(self, filename, bbox_inches):
+        bbox = self.figure.dpi_scale_trans.transform_bbox(bbox_inches)
+        h = self.figure.bbox.height
+        img = Image.open(filename)
+        img = img.crop((bbox.x0, h - bbox.y1, bbox.x1, h - bbox.y0))
+        img.save(filename, format=img.format)  # TODO: also copy metadata
+
 
 @_Backend.export
 class _BackendAgg(_Backend):
diff --git a/lib/matplotlib/backends/backend_pdf.py b/lib/matplotlib/backends/backend_pdf.py
@@ -2737,6 +2737,32 @@ def draw(self):
         _no_output_draw(self.figure)
         return super().draw()
 
+    def adjust_bbox(self, filename, bbox_inches):
+        bbox = self.figure.dpi_scale_trans.transform_bbox(bbox_inches)
+        # What about PdfPages?
+        with open(filename, "a+b") as file:
+            file.seek(0)
+            buf = file.read()
+            page_pos = file.tell()
+            pageid = self.figure._cachedRenderer.file.pageList[-1].id
+            page_match = re.search(
+                rb"(?s)%d 0 obj\n.*?/MediaBox.*?\nendobj\n" % pageid, buf)
+            file.write(re.sub(br"/MediaBox \[[^]]*\]", b"/MediaBox %s"
+                              % pdfRepr(bbox.extents.tolist()), page_match[0]))
+            startxref_pos = file.tell()
+            file.write(b"xref\n")
+            file.write(b"0 1\n0000000000 65535 f \n")
+            file.write(b"%d 1\n%010d 00000 n \n" % (pageid, page_pos))
+            file.write(b"trailer\n")
+            trailer_match = re.search(
+                rb"(?s)trailer\n<< (.*) >>\nstartxref\n(\d+)\n%%EOF",
+                buf[buf.rfind(b"trailer\n"):])
+            file.write(
+                b"<< %s /Prev %s >>\n" % (trailer_match[1], trailer_match[2]))
+            file.write(b"startxref\n")
+            file.write(b"%d\n" % startxref_pos)
+            file.write(b"%%EOF\n")
+
 
 FigureManagerPdf = FigureManagerBase
 
diff --git a/lib/matplotlib/backends/backend_svg.py b/lib/matplotlib/backends/backend_svg.py
@@ -7,6 +7,7 @@
 import itertools
 import logging
 import os
+import pathlib
 import re
 import uuid
 
@@ -1347,6 +1348,17 @@ def draw(self):
         _no_output_draw(self.figure)
         return super().draw()
 
+    def adjust_bbox(self, filename, bbox_inches):
+        bbox = self.figure.dpi_scale_trans.transform_bbox(bbox_inches)
+        buf = pathlib.Path(filename).read_text()
+        w, h, x, y = map(short_float_fmt, [
+            bbox.width, bbox.height,
+            bbox.x0, self.figure.bbox.height - bbox.y1])
+        buf = re.sub('width="[^"]*"', f'width="{w}pt"', buf, 1)
+        buf = re.sub('height="[^"]*"', f'height="{h}pt"', buf, 1)
+        buf = re.sub('viewBox="[^"]*"', f'viewBox="{x} {y} {w} {h}"', buf, 1)
+        pathlib.Path(filename).write_text(buf)
+
 
 FigureManagerSVG = FigureManagerBase
 
