The test demanded a full halo on every side except the frame's own
edge, but a tile one step in from it is grown to the edge and no
further, exactly where the untiled render stops too.
DemosaicedImage::linear_rgb16_window uploads part of a linear DNG, or a
box-reduced copy of it, and says where it sits in the frame; size() now
reports the frame and texture_size() the texels, and the fused pass
writes the window into the shader's uniforms. EditGraph::source_region
finds the part of the source a view reads, and tiles::plan cuts a render
too large for one texture into halo-grown, grid-aligned tiles.
The GPU test renders frames a tile at a time from their own windows and
compares them with the whole: identical for point operations, within one
code value when straightened with clarity on.
dtourolle