/* =======================================================================
   THE AURA, a cursor-modulated Gabor field laid over the whole page.
   ======================================================================= */


  /* ── THE REFERENCE, AND WHAT WAS ACTUALLY TAKEN FROM IT ───────────────
     pixlpa, "Gabor FM Gradient Study 1" (hicetnunc 32293). A Gabor wavelet
     is a sine wave multiplied by a Gaussian envelope; the piece sums a
     handful of them and runs a MODULATOR pass that varies each wavelet's
     frequency by spatial lookup, so the bands wander instead of marching.

     Measured off the file rather than described from memory: its structure is
     DUAL-FREQUENCY. Everything is either very low frequency, soft colour
     fields with no edge shorter than about 60px of ramp, or very high
     frequency, a hard 4-6px line screen carrying only 8-15 levels of
     amplitude. The mid band is empty, and that emptiness is the look. Both
     halves are reproduced here: the canvas carries the wavelets, the rule
     below carries the screen.

     ── WHY IT IS OVER THE PAGE AND NOT BEHIND IT ────────────────────────
     This is the one decision that matters. Every band on this page wears the
     measured ground of the works standing in it, exactly, so a plate has no
     visible edge: that is the page's whole construction, and the tokens file
     records moving --g-orange two units rather than re-seat an artist's file,
     because at a flat seam 2/255 reads.

     A reactive gradient painted BEHIND the content would modulate the room
     while the artwork, a flat JPEG of that same ground, stayed fixed. Every
     work on the page would acquire a visible rectangle the moment the cursor
     moved. Laid OVER everything, the field crosses the plate boundary with
     the same value on both sides, so the seam stays invisible and the works
     stay dissolved in their rooms. The reference does the same thing: its
     screen is an overlay, not an underlay.

     It is therefore LIGHT, not background. Which is also why it is
     achromatic: soft-light preserves the hue underneath it, so the red room
     lights red and the green room lights green without this layer
     introducing a single colour of its own. The artwork keeps supplying all
     the colour on the page. */
  /* ── IT LIGHTS THE ROOMS, IT DOES NOT SIT ON THE WORK ────────────────
     z-index 1 puts the field above each band's ground and BELOW every work
     and every line of type, which are lifted to 2 by css/18-atmosphere.css.
     It was 3, over the whole page: light laid on top of an artwork is a
     filter on the artwork, and this page's only colour is meant to come from
     the work itself.

     soft-light keeps that true even here. It preserves the hue underneath
     and moves only luminance, so the red room lights red and the green room
     lights green, and this layer introduces no colour of its own anywhere. */
.aura{position:fixed;inset:0;z-index:1;pointer-events:none;
    mix-blend-mode:soft-light;
    opacity:0;transition:opacity 1.2s var(--ease);
    contain:strict}


.aura.live{opacity:.62}


  /* full device resolution, evaluated per pixel in a shader. There is no
     upscale here and nothing to interpolate, which is the whole point: see
     js/18-aura.js for why the first canvas build read as low-resolution
     grading. */
.aura canvas{width:100%;height:100%;display:block}


  /* ── NO LINE SCREEN ──────────────────────────────────────────────────
     The reference carries a hard 4-6px diagonal screen at 8-15 levels, and
     it was reproduced here as a repeating gradient masked to a pool that
     followed the cursor. It is removed.

     It was the one piece of STRUCTURE in a layer whose whole job is to have
     none. A crisp repeating pattern laid over flat rooms of measured colour
     is a texture on the page, and at any amplitude you can see it reads as
     an overlay rather than as light. The reference can carry it because the
     screen is part of a picture; here the picture is Movsum's, and the only
     structure on this page should be his.

     What is kept from the reference is the part that matters: the wavelets,
     the frequency modulation, and the dithered ramp. */


@media (prefers-reduced-motion:reduce){
    .aura{transition:none}
    /* the field is drawn once and left still: see js/18-aura.js */
}