使用 Reportlab 在 PDF 中保存 SVG 时出现不透明度问题

Question

I have this SVG file:

<svg version="1.1" viewBox="0 0 390 390" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
    <line class="arrow" opacity="0.5" stroke="#15781B" stroke-linecap="butt" stroke-width="9.0" x1="307.5" x2="279.60592002787337" y1="352.5" y2="296.7118400557468" />
    <polygon class="arrow" fill="#15781B" opacity="0.5019607843137255" points="264.51246117974983,266.5249223594996 264.5124611797498,304.25856947980856 294.69937887599696,289.165110631685" />
    <text fill="white" font-size="11" font-weight="bold" opacity="0.5" x="264.0" y="291.0">DEF</text>
    <line class="arrow" opacity="0.5019607843137255" stroke="#15781B" stroke-linecap="butt" stroke-width="9.0" x1="262.5" x2="262.5" y1="307.5" y2="255.75" />
    <polygon class="arrow" fill="#15781B" opacity="0.5" points="262.5,222.0 245.625,255.75 279.375,255.75" />
    <text fill="white"  font-size="11" font-weight="bold" opacity="0.5" x="252.0" y="249.0">ABC</text>
</svg>

If you save it as a b.svg file, and open it, you will see that there is some overlapping with opacity: the text ABC and DEF is readable .

Now when I render it in a PDF file with the well-known method from Generating PDFs from SVG input :

from svglib.svglib import svg2rlg
from reportlab.graphics import renderPDF
drawing = svg2rlg("b.svg")
renderPDF.drawToFile(drawing, "b.pdf")

then the opacity is lost in the PDF file, and the left part of the D letter of "DEF" is unreadable:

Question: How to include a SVG into a PDF and keep the opacity?

Answer 1

A quick look at the svglib code shows that svglib does not parse the "opacity" attribute, but it does parse the "fill-opacity" and "stroke-opacity" attributes. So changing your svg to

<svg version="1.1" viewBox="0 0 390 390" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
    <line class="arrow" fill-opacity="0.5" stroke-opacity="0.5" stroke="#15781B" stroke-linecap="butt" stroke-width="9.0" x1="307.5" x2="279.60592002787337" y1="352.5" y2="296.7118400557468" />
    <polygon class="arrow" fill="#15781B" fill-opacity="0.5019607843137255" stroke-opacity="0.5019607843137255" points="264.51246117974983,266.5249223594996 264.5124611797498,304.25856947980856 294.69937887599696,289.165110631685" />
    <text fill="white" font-size="11" font-weight="bold" fill-opacity="0.5" stroke-opacity="0.5" x="264.0" y="291.0">DEF</text>
    <line class="arrow" fill-opacity="0.5019607843137255" stroke-opacity="0.5019607843137255" stroke="#15781B" stroke-linecap="butt" stroke-width="9.0" x1="262.5" x2="262.5" y1="307.5" y2="255.75" />
    <polygon class="arrow" fill="#15781B" fill-opacity="0.5" stroke-opacity="0.5" points="262.5,222.0 245.625,255.75 279.375,255.75" />
    <text fill="white"  font-size="11" font-weight="bold" fill-opacity="0.5" stroke-opacity="0.5" x="252.0" y="249.0">ABC</text>
</svg>

should do the trick.

UPDATE

This seems to be an open issue since 2018

Answer 2

To long for a comment and the Kudos / Bonus should go to @zap for pointing me at rebuilding all the shapes to Polygons which worked significantly better than Rect.

I still struggle to understand twice so as to get WkHtmlToPDF to give me a good scalar PDF but it did give me transparency with the following.

<svg version="1.1" viewBox="0 0 390 390" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
    <polygon class="arrow" fill="#15781B" fill-opacity="0.5" stroke-opacity="0.5" points="275.75,298.6 283.6,294.6 312,350.5 303.5,354.5" />
    <polygon class="arrow" fill="#15781B" fill-opacity="0.5" stroke-opacity="0.5" points="264.5125,266.5249 264.5125,304.25856 294.6994,289.1651" />
    <text fill="white" font-size="11" font-weight="bold" fill-opacity="0.5" stroke-opacity="0.5" x="264.0" y="291.0">DEF</text>
    <polygon class="arrow" fill="#15781B" fill-opacity="0.5" stroke-opacity="0.5" points="258,255.75 267,255.75 267,307.5 258,307.5" />
    <polygon class="arrow" fill="#15781B" fill-opacity="0.5" stroke-opacity="0.5" points="262.5,222.0 245.625,255.75 279.375,255.75" />
    <text fill="white"  font-size="11" font-weight="bold" fill-opacity="0.5" stroke-opacity="0.5" x="250" y="250.0">ABC</text>
</svg>

Here are the transparent objects on a transparent background on a snowy day. Somewhere there must be a means to fix scaling but I did not find it yet and others have said similar.

The Idea was to keep a minimal as possible approach without any special external adjustments (though I did try many). So the SVG was included as img in an HTML "square" block.

"test1.htm"

<!DOCTYPE html>
<html>
  <head>
  <style>
    body {background: transparent;}
  </style>
  </head>
  <body>
    <img src="file:///wkhtmltox\bin\test1.svg" height=390px width=780px />
  </body>
</html>

and called directly

wkhtmltopdf.exe --enable-local-file-access  --disable-smart-shrinking --no-background --no-pdf-compression -n "test1.htm" test1.pdf

In the spirit of maintaining opacity I included that aspect in the body style and external --no-background but they normally would not be required And finally I seem to have got scaling stable so here is the SVG in an A4 transparent page.