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Avoid blurry rendering of SVG paths in Chromium

<2019-11-04 Mon>

In the past few days, I am on a project of rendering PDF files to SVG files. After some hard work, I finally managed to implement the renderer, though some features, like translucent images, were not well supported.

With my PDF to SVG renderer, I conveniently got many perfect SVG files from a testing PDF file set. Yeah, these SVG files were perfect when I viewed them with Firefox, Inkscape, or even gThumb. But soon I found when I viewed them with Chromium, some of them are not that perfect. A few characters were too blur to recognize.

This image is a screenshot of Firefox:

And this is the same file in Chromium:

I'd better fix this as the Chromium (and Chrome) is the most popular browser nowadays. I tried many vain approaches, like trying any possible value of the shape-rendering attribute for the SVG files, and none of them worked.

I didn't know how Chromium renders SVG, but I saw that in the blurrily rendered SVG file, not all of the characters were murky. So, I thought if I could finger out the difference of the SVG elements which contained the clear characters and the murky characters, I would get the reason. It proved a successful try. I found the murky characters were in path SVG elements who had a very large value for their d attribute while the clear ones were in elements with small d attribute.

There must be a threshold of the size of d attribute, if a path element has a value of d larger than it, Chromium will render that path blurrily. But, instead of going to find that threshold, I fix my problem empirically: I broke paths represented long texts into smaller paths corresponding to short texts. In my case, it is fine to regard text with less than 6 Chinese characters as short text.

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