`write_texture` differed from `write` by one argument, which is what the
generic parameter was already for, so textures register as a primitive
with a `TexturePrimitive` holding the slot. `write_texture`,
`InstanceKind` and the layer's separate texture list are gone;
`DrawLayers` is back to `write` and `free`, with the kind carried in
`PrimitiveInst` as it carries everything else.
What differs between a texture and a rect is only what it samples, so
that is what registration says: `PrimitiveTexture::Atlas` binds the
shared atlas once for the layer, `PerInstance` binds the texture its own
data names and draws one instance at a time. One loop over a layer's
lists, one match on that.
`Pod` is back to being a supertrait of `Primitive` rather than the bound
itself. The guarantee is that a `PrimitiveKind<P>` is only minted by
`register::<P>` and `write` takes the kind and the value together, so a
primitive always has a list of its own to go in and the write does not
check anything: a list takes its stride from the type it was made for
instead of inferring it from the first write and asserting on the rest.
Also from reviewing this: a layer's lists and their buffers are created
only when that layer draws that primitive, so a primitive nobody uses no
longer costs two buffers in every layer -- which matters more now the set
is open-ended. `ListBuffers::update` takes the two things it uses rather
than the whole pipeline.
Verified again over all five cases: an image alone in a layer, three
images added and one deleted, the masked text-edit tab, the text-layout
tab and the default tab.
iris
7b318e3271