[1.1.104] Trilinear filtering between incompatible mipmaps

[xykite]

This is a minor but noticeable rendering issue that arises from the combination of two non-bugs:

1. Icons have flags 'linear-minification', 'linear-magnification', 'linear-mip-level'. So if the game interface has a UI scale that results in icon sizes between mipmap levels (i.e. UI scales 75, 125, 150, 175 for most icons) then they are rendered with trilinear filtering.
2. Some icons (predominantly in __core__/graphics/icons/mip) have mipmaps that do not appear to be proper mipmaps: instead of being downscaled, they look like slightly different renderings at a lower resolution.

Neither 1) nor 2) is an issue by itself: 1) only means you have trilinear filtering with valid mipmaps, and 2) only means when you zoom in or out, you snap between different icons without blending them. However with both at the same time, you are blending two images that are not compatible, which can result in visual artefacts.

The most obvious places where 2) applies are __core__/graphics/icons/mip/slot_ammo_white.png and __core__/graphics/icons/entity/character.png, which are often visible in the GUI. Here I have superimposed the largest mip level (cyan) over the second-largest (red, 2x upscaled with no interpolation).

mipdiff.png (4.39 KiB) Viewed 266 times

For slot_ammo_white.png it appears the relative scales and positions of the two mip levels are different, so when they are trilinear-filtered there is visible blurring.

Similarly for character.png, the mipmaps don't quite align. As a result the icon appears blurred at UI scale 125 and the 'ghosting' effect on the RHS is really obvious at UI scale 150.

badblending.png (61.76 KiB) Viewed 266 times

I have checked this issue does not just affect me: looking at screenshots other people have posted on Discord over the past week or so, every image I have found that contains an equipment bar at UI scale 125 or 150 appears to have this problem (red boxes are mine, everything else isn't).

discord.png (205.76 KiB) Viewed 266 times

Expected result: Here is what I believe it is meant to look like at scales 125, 150. I have turned off trilinear filtering by removing the linear-mip-level flag from both SpriteOption::Icon, and 'icon' in SpriteFlagHelpers::optionsList. The blurring / ghosting has gone.

noblending.png (59.52 KiB) Viewed 266 times

[xykite]

Note I believe this report is technically a dupe of 93236. To repro that issue, here is a combinator with a checkmark on it

blurry-check.png (33.47 KiB) Viewed 261 times

I believe the reason the glitch is happening is an incorrect mipmap (possibly the only bad one in __base__/graphics/icons). The two levels are superimposed as in my first post.

checked-green.mipdiff.png (689 Bytes) Viewed 261 times

Here is the same combinator after removing the 'linear-mip-level' flag from SpriteOption::Icon :

nonblurry-check.png (28.5 KiB) Viewed 261 times

Edit: for completeness here's the fix the other way round - i.e. by correcting the mipmap but keeping trilinear filtering enabled:

checked-green.png (859 Bytes) Viewed 186 times

fixed-mipmap.png (34.54 KiB) Viewed 186 times