Using non-default samplers

[obs1dium]

I've been playing around with the lens blur filter and noticed that it tends to produce ugly artifacts near the image edges, especially when using a large blur radius.
Using samplers with their address mode set to 'mirror repeat' alleviates this.
However, simply setting the input images sampler is insufficient, as the filter generates intermediate images which appear to fall back to the default sampler.
I tried two things:

• explicitly 'forwarding' the input image's sampler in the filter to the intermediate images, i.e. calling imageWithSamplerDescriptor a bunch of times
• replacing the samplers in the shader code by 'properly' configured ones

Both approaches worked, but maybe there's a better way?

[YuAo]

Lens blur filter is not so much tuned so there may be other problems. The main idea is based on https://colinbarrebrisebois.com/2017/04/18/hexagonal-bokeh-blur-revisited/

About your question, I think both way is ok. I personally prefer the “fowarding” way. It gives the caller an opportunity to choose a different address mode (maybe clamp_to_edge works well too?)

You can send pull requests if you’d like to refine the lens blur filter.

[obs1dium]

I think 'clamp to edge' is the default, 'mirrored repeat' is really the only address mode that minimized edge artifacts for me.

[YuAo]

The default sampler address mode of MTIImage is “clamp to zero”. We think this is the most logical default address mode - when you read a pixel outside an image you get zero.

[obs1dium]

Ah, you're right, I was looking at the Metal language specs, not the MTISamplerDescriptor implementation.