The owner's clue was the whole diagnosis: the same image looked fine at
220px in the hover preview and bad at 150px in a card. So not the source,
and not the URL variant either -- every Qt producer picks exactly what
Slint picks, `large` (600px) into a 200px cell, 3x headroom.
`artwork_qt` was producing the right derivative and `RoundedImage` was
drawing the untouched 600px original next to it. `Context2D.drawImage`
does not filter, so every card was a nearest-neighbour downscale: measured
on a card cropped out of the running binary, RMSE 0.000 against a
point-sampled reference. The preview looks right because it is a plain
Image with smooth+mipmap and never touches this path.
Three defects were latent behind that dead derivative: `thumbnail(w,h)`
does not preserve aspect (46 square covers on disk written as 32x28),
`to_rgb8` matted transparent logos onto black, and the file was JPEG q75 --
more damage than the resample it was meant to cure.
Qobuz playlist art is 800x380, and both the header and the card were
stretching it to fill a square. It now keeps its ratio, and the uncovered
area takes a gradient derived from the image itself, reusing the ambient
colour pipeline rather than starting a second one.
cc
vicrodh
6b5226acf9