Get a pixel perfect match WMS image

[sbrunner]

To avoid having little blurry image

Fix #14718
Thanks @mike-000

[github-actions]

📦 Preview the website for this branch here: https://deploy-preview-14719--ol-site.netlify.app/.

[sbrunner]

@mike-000 are you allowed to review this pull request?

[jahow]

Thanks @sbrunner! I think I understand the change but maybe having a rendering test specifically for this would be good? The unit test does not provide much explicit guarantee of having a crisp final render.

[tschaub]

Does this result look worse before this change?

I'm not sure I would call this as a "pixel perfect match" compared to the input tile:

[mike-000]

Using a data url might be better test. Currently with a ratio which is an odd fraction of the frame size you get blurring - in https://codesandbox.io/s/simple-forked-qivyjj?file=/main.js red and green pixels are interpolated as #808000 or #7f7f00 but if the ratio is changed to an even fraction e.g. 384 / 256 it is a bright mosaic of the two colors. With the fix that should be seen with any ratio.

[tschaub]

I'm not sure what to make of that sandbox example.

I was anticipating that this fix would make it so a previously blurry map was now less blurry. The code change looks to me like it could accomplish that. I assume it would be possible to demonstrate this with a test. I don't understand why a data url would be required for this.

[mike-000]

The data url creates a pixel mosaic which makes the blurring very obvious when magnified

[tschaub]

Is this change meant to fix a real-world example that can be represented in a test?

[mike-000]

Based on the example in #14718

Current blurry
https://codesandbox.io/s/wms-image-custom-proj-forked-2uon5w?file=/main.js

With the fix applied as patch
https://codesandbox.io/s/wms-image-custom-proj-forked-2tl14y?file=/main.js

[fredj]

I've changed the rendering test for the original example in #14718

The image still looks blurry here on GitHub but it's not the case, see:
https://raw.githubusercontent.com/sbrunner/openlayers/blury/test/rendering/cases/source-imagewms-blurry/expected.png

[sbrunner]

Hello,
with the test written by @fredj, is it OK to be merged?

[jahow]

All good! I ran the test without the changes and indeed the result is blurry:

I think we spent enough time looking at the Bourdonnette post office so I'm approving, thanks @sbrunner @fredj and @mike-000!

[tschaub]

I agree it looks good. Thanks all for the improvement.

[sbrunner]

Thanks :-)