Do browsers really use a box filter to approximate a gaussian blur? That seems implausible to me, as they produce pretty different looking blurs.
It doesn't seem improbable considering it's a huge performance win and perhaps many won't notice?
It is the performance win for similar looking results that I find improbable. For a box blur to look like gaussian blur, you would need multiple passes. Even though each pass is now O(1) instead of O(n) (with n the blur radius), due to caching effects I think a gaussian kernel would still be faster, especially for the small blur radius as described in the article.
Yeah because the GPU has special hardware which you can take advantage of for an optimized box filter.
https://www.rastergrid.com/blog/2010/09/efficient-gaussian-b...
That link is not a box filter, as it still uses weights to approximate a gaussian convolution kernel. It just uses some special hardware to do less texture fetches. But that is a constant 2x improvement over the full 1D convolution, not the box filter O(1) approach that the article suggests that browsers are using.
You've moved me a place of uncertainty here. I had some confirmation that _some_ browsers use box blurs for this effect, I _know_ some game engines use multiple box blurs to approximate Gaussian blur (having seen the code myself).
I updated a few sentences in the article to reflect that uncertainty. Thanks!