At low zooms, tiles with transparency can disappear

[eishiya]

It seems that as of Tiled 1.10, Tiled employs a different image sampling method when the view is zoomed out. While mostly fine, it seems to be a variant of Nearest Neighbour that can cause tiles with transparent pixels to entirely disappear at low zooms.

For example, here is a map filled with one tile on the left and another on the right. The left tile is fully opaque, mostly green, but with a teal shadow. The right tile is mostly beige, but with some transparent pixels on the right side. The tiles are 16x16.

Zoomed in view showing details of the tiles, so you can see the teal and transparent pixels.

6% zoom. The left tiles all blend into a solid green mass, that happens to match the dominant green colour of the tiles. The right tiles merge into a dark beige mass, a colour not from the tiles. This is all fine.

3% zoom. The left tiles all the teal from the shadow/border, while the right tiles are all transparent. In both cases, it looks like the bottom right pixel from the tiles is sampled, instead of blending colours from more of the tile. Not only does half the map appear gone, the tiles that are visible don't look as one might expect.

I think this is new in Tiled 1.10, I think 1.9.x and earlier used a different image sampling method that produced blurrier but more representative results. I wonder if this resampling method is tied to #3656 (lag when drawing large maps zoomed out), either as a cause, or as Qt's attempt to mitigate potentially worse lag by sampling fewer pixels.

I am using Tiled 1.10.1 64-bit on Windows 10. Hardware rendering is off.