Nobody can refine an edge they are not being shown. The only thing drawn on
the canvas was the region overlay — a false-coloured picture of what the model
*detected* — which knows nothing of a layer's feather, its falloff, its
morphology, its invert or its opacity, and nothing at all about a gradient, a
range or a stroke. Every control added for mask editing therefore acted on
something invisible, which is why the whole feature reads as absent rather
than as unfinished.
A layer's finished mask now draws over the photograph in one of three styles:
a tint for whether the right thing is selected, an alpha for where the edge
is, an outline for whether that edge is registered against the detail the
other two hide.
The hard part is not the shader. A selection with no adjustment on it changes
no pixel, so it is not active, so it holds no slice of the mask array and is
never rasterised — and that is exactly the layer somebody wants to look at,
for the whole of the time between choosing a subject and deciding what to do
to it. So `MaskStack::rendered` is `active()` plus the layer being looked at,
and the rasteriser, the composer and the distance-field builder all index by
position in it. Which is also why the design's "two uniforms, no recompile" is
not available: a uniform can select a slot, it cannot conjure one.
The reveal is never on the graph. It reaches the pipeline as an argument to
`compose_revealing`, and `compose_for` — which the exporter, the thumbnail and
the neutral probe all call — has no way to ask for one. A flag on the graph
would have been shorter, would have type-checked, and would have been one
forgotten reset away from a red tint baked into an exported file.
And the tools that shape a mask now arm. `Masking.tool` is an `in` property
only Rust may write, and the handler wrote nothing back, so the strip reported
"Select" however many times Paint was pressed and the paint area was never
enabled — the brush, the parts and the whole of FR-DEV-19b reachable from no
control in the application.
The region overlay stands down while a mask is being shown, and its button now
says what it hides: two overlays that look alike and mean different things is
worse than either.
A mask the model draws arrives approximately right — stopping inside a
shoulder, leaking into the hair — and FR-DEV-3's edge controls move the
*whole* boundary, so no value of feather or dilation fixes two errors that
go opposite ways. What fixes them is a second selection joined to the first,
and a layer that held exactly one source had nowhere to put one. The brush
the core has had all along was reachable from no control in the application.
A layer is now an ordered list of parts. Each names a source and how it
joins the mask before it — added to it, or taken out of it — and carries its
own edge treatment, because a model's soft coverage and a stroke painted
where it stopped short do not want the same feather. Invert and opacity stay
on the layer, where the composed shader already reads them.
The sidecar grows `[part]` blocks and nothing else. A layer of one part
writes exactly the bytes it always did; a mask block with no part blocks
after it reads back as one part; and a stroke, a join or a source this build
cannot read costs that part rather than the layer. So every sidecar in every
library still parses to the edit it always was.
On the device the parts fold into the layer's one slice, so eight layers
still cost eight channels: union is a `max` blend and subtraction is the
erase blend the brush already used. A part is drawn into a scratch texture
before it is joined, and that is not incidental — an erase stroke means a
hole in *that part*, not a hole in the mask, and drawn straight onto the
accumulator it would punch through the subject underneath. A layer of one
part skips all of it and takes the path it always took.
In the interface: a part list under the selected layer with a chip saying
which way each joins, Add and Subtract beside it, a Select/Paint/Erase strip
with the brush's size, hardness and flow, and a drag on the photograph that
paints. Pressing Paint on a mask that cannot hold a stroke joins a part that
can, rather than explaining that a subject is not a brush. A whole stroke is
one step in the history.
The edge controls now shape the part that is selected rather than the layer,
which is the one behaviour change to an existing control: with a correction
selected, the feather slider softens the correction and leaves the model's
mask alone.
The auto masks arrive in a second and cannot then be changed by a pixel: no
brush, no way to cut one selection out of another, no way to drag a boundary
that stopped inside a shoulder, and no way to see the alpha a layer actually
produces — the canvas overlay draws what the model detected, not the mask.
docs/mask-editing.md is how that closes. A layer stops holding one source and
holds an ordered list of parts, each naming how it joins the mask before it,
so painting on an auto mask, subtracting, and intersecting a subject with a
luminance band are all one mechanism. Notes what the tree already has (the
whole brush is written and reachable from no control), what the set operations
actually cost (three blend states, no new texture), why the edge push is a
warp rather than a local morphology, and why painting has to draw
incrementally. Ends with the four decisions the build needs first.
dtourolle