some hillshade rendering issues

[farfromrefug]

Hi,
I am working again on hillshading. The reasoning is to make smaller hillshade mbtiles with a better rendering.
For reference the technique used is this https://medium.com/@frederic.rodrigo/optimization-of-rgb-dem-tiles-for-dynamic-hill-shading-with-mapbox-gl-or-maplibre-gl-55bef8eb3d86

Now in the process of working on this i discovered rendering issues with hillshading in carto. It does not only happen with optimised mbtiles.
So until maxzoom it draws fine.
But when i start to overzoom i start to see some errors in some areas. And when i zoom a lot it goes into "line" mode.
What bugs me the most is the artifacts appearing in some regions.
As a comparaison in the last screenshots, it works just fine in mabpox.

I wondering if it comes from the fact that carto creates a "normal" image before rendering it with a shader. I think mapbox does it all in a shader.
TBH i am a bit lost with the whole tile(image) processing in carto for now. Wondering, while overzooming, is the normal map created on a scaled image or on the original image?

[mtehver]

@farfromrefug I think I may know the reason here - SDK automatically upscales bitmaps after 'maxzoom' is reached. In case of hillshading, this may cause artifacts and should be likely implemented differently. I need to think about this a bit more, though.

[farfromrefug]

@mtehver i tested your changes and it works perfectly.
I had to make a quick fix on exageration though.On overzoom exageration was "increasing"
Akylas@b07c869
I did not create a PR cause my code there is different. Let me know if you want me to create one

Thanks!!!!!

EDIT: i am not sure if it a regression. But i see my app hanging when i quickly zoom in/out. Not happening without hillshade. Will try to run some test with older versions. Do you have any idea?
PS: i can share hillshade mbtiles if you need

[farfromrefug]

@mtehver i can confirm your last changes on hillshade made the app much slower. It keeps on hanging. I rollback to a build before and it is smooth again. Haven´t looked at the code yet to see what might be happening

[mtehver]

@farfromrefug Is this noticeable at all zoom levels? Processing became more expensive at 'overzoomed' tiles, for other tiles should be roughly the same. I will see if this can be optimized.

[farfromrefug]

@mtehver i would say all but I need to test further.

[farfromrefug]

@mtehver i compared with all framework and the difference is obvious. It is much slower whatever the zoom level, even not overzoomed