A clipped photosite reaches the merge as (1, 1, 1), which the as-shot
balance turns magenta. The preview balanced it with no highlight rule at
all, so every blown cloud was pink on the alignment page. The DNG had the
quieter form of the same fault: a frame's gain below one moved a blown
sample off the white level, and a feather mixed it into a neighbour's
real sky, so the develop's own desaturation no longer recognised it.
The merge shader and the preview now write a blown sample, before the
gain, as the camera value the composite's balance calls grey — the
develop pipeline's neutral, fading in from CLIP_ONSET.
The fused shader stored black with alpha 1 for a pixel whose source
coordinate left the frame, and the merge's warp averaged it in like any
other: a dark, badly interpolated fringe along every frame's edge, visible
as a seam wherever a frame ended and, later, as the edge the border fill
continued. The display keeps its opaque black; CameraLinear stores alpha 0
and the warp weights each sample by the alpha it interpolated, dropping a
sample that has none.
merge.wgsl warps one camera-space tile into one output chunk — output
pixel to direction (the projection maths of dr_pano::projection, verbatim),
direction to the frame's camera, camera to source pixel, bilinear by hand
from four textureLoads because rgba32float is not filterable — and adds it
into a storage-buffer accumulator weighted by its distance from the
frame's edge. A resolve pass divides by the weights and packs sixteen-bit
samples at the sensor's scale with a coverage bit.
MergePass::merge drives it: bands of rows, chunks across a band, and for
each chunk only the frames whose footprint meets it, each rendered as the
source rectangle the chunk needs and nothing more. The working set is one
chunk, one tile and one band (FR-MRG-11); the frame textures are the
caller's to cache. Feathered, not seamed; gain a scalar per frame — the
blend quality is panorama.md §10's step 5, after the path writes a file.
dtourolle