Re: [Algorithms] Blurring in HLSL

[Ivan-Assen I. <iva...@gm...>]

> Second, you can calculate the Gaussian blur in a single post-processing
> pass if you want. It's no different from doing the horizontal and
> vertical in two different passes, except for the amount of math
> involved. If you do that, then you'll be using a large amount of pixel
> shader instructions compared to framebuffer writes, which will generally
> be slower than just doing two separate passes on render targets. All
> hardware is decent enough at fill rate compared to shader instructions
> that it doesn't make sense to try to do it in a single post-process
> pass. When we get a 1000:1 ratio of shader ops:framebuffer writes, that
> detemrination may change, but we're nowhere near there just yet :-)

I beg to disagree - it still depends on the particular hardware and
filter sizes.

There's this weird piece of hardware that has
sold in the mid-two-digit millions, yet refuses to sample from its framebuffer,
so if you're doing two passes, you have to do transfer the results from the
first pass into RAM, and 5x5 and 9x9 Gaussian kernels turn out faster
in one pass instead of separated in H and V.