At preview scales from 0.75 to 1 footage keeps native pixels, a proxy sets
its own buffer scale at any render scale, a Preserve Resolution precomp is
drawn at full size, and earlier effects can pad or offset the buffer, so
snapping to the preview grid could pick a different ID than the rendered
matte. Use the scale and offset of the buffer the Cryptomatte effect
receives (layer_input, rendered once and then cached).
The pixel centre goes to an aux point through effectcraft_effects::aux_point,
which index_map_at now calls too, so the two round identically (a division
vs the reciprocal picked the other ID on a 104 px proxy of 1920 px footage).
An unknown effect uid errors "no such effect" and a layer without pixels
"this layer has no pixels", as effect.pickColor does.
Engine part of viewer picking: replace / add / remove the top-coverage ID at a
layer-space point in one undo step, at the time the Selection was read. The
aux channels come from the render's own path (Renderer::layer_aux, shared with
the effect host; footage at its source time, 3D precomps) through a renderer
set up like Session::render (expressions, render prefs, layer cache). An
optional scale snaps the point to the pixel a preview at that resolution
samples. New effects::crypto_select quotes names and falls back to <hex> for
unnamed, wildcard-looking or ambiguous names. effect.cryptomatteAt is the
read-only hover query.
Matej Kozlovský