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Very slow svg rendering since version 53.0

See original GitHub issue

The time it took to create a pdf with multiple svg images increased drastically. We used to create some figures via matplotlib and base64 encode those images, so we do not have to create image files:

from io import BytesIO
import base64

from matplotlib.figure import Figure
import weasyprint

fig = Figure(...)
...
buffer = BytesIO()
fig.savefig(buffer, format='svg')
img_str = base64.b64encode(buffer.getbuffer()).decode("ascii")
html_image = f"<img src='data:image/svg+xml;base64,{img_str}' />"
weasyprint.HTML(string=f"<html><head></head><body>{html_image}</body></html>").write_pdf(...)

We also tried to use svg html tags (without base64 encoding) instead but this took way too long as well (plus there is some issue with namespaces (ElementTree.fromstring exception) so we had to use some regex sub stuff to remove metadata an namespace data from the svg xml).

Results from cProfile for the method write_pdf (the underlying draw methods got called 15 times each):

Prior to 53.0: time: 8602 ms, 31.7%
After 53.* update: time: 28502 ms, 71.4%
Using html svg tags: time: 23376 ms, 68.7%

Those stats got worse the more svg images where included.

Issue Analytics

State:
Created 2 years ago
Comments:9 (7 by maintainers)

Top GitHub Comments

1reaction

SvenBeckercommented, Sep 10, 2021

Ok thank you for the response. I opened two new issues. Btw. is there some documentation on how to use optimize_size or image_cache. I was not really aware of it and now I’m not really sure hot to use it.

0reactions

liZecommented, Sep 11, 2021

Caching use tags makes the speed closer to what it was. There’s room for improvement, but I think that it’s enough for this performance problem.