Chrome shaders#

A frame is a rect too, so it is a pass too. where="chrome" on any entry in shaders or in a states block runs that pass over a pane's frame — border, padding, title, buttons — instead of its contents.

states {
    // a bell nobody has answered: a quarter-second flash, then gone
    bell { tint where="chrome" channel="fg" color="#ffcc00" amount="(since < 250) * 255" }
}

Nothing else changes: same shaders, same amount, same expressions, same chain order. One new word.

You have already seen one: the default bell flash — blinks then a breathe on the frame of a pane that rang, in theme's bell colour — is exactly this, a chrome tint whose amount reads since. (The shimmer that crosses the pane's body at the same moment is the same idea without the new word: an ordinary content pass in the same chain.) Writing your own bell { … } replaces both; bell_indicator false silences them with the mark.

Two rules#

channel="fg", almost always. A border's background is the terminal's own default; mixing that towards a colour paints a rectangle behind the glyphs instead of colouring them, and leaves it there until the pane changes state. fg also keeps the padding inside the border out of it, since a blank cell has no foreground to colour — so the effect lands on exactly the rules, the title and the buttons.

The contents are cut out of the pass. A full-strength chrome tint cannot reach your text, and a full-strength content tint cannot reach the border. They are two rects and two passes.

Positions are the whole frame's#

x/y are counted from the frame's top-left corner, with cols/rows the size of the pane's rect — not of one side. One pass over the whole ring, so an effect can travel round a border instead of restarting at every corner.

For anything that travels, though, the coordinate you want is distance along the ring, which the language can work out — clockwise from the top-left:

(y == 0 ? x : x == cols-1 ? cols - 1 + y
 : y == rows-1 ? 2 * cols + rows - 3 - x : 2 * cols + 2 * rows - 4 - y)

with the perimeter itself 2 * cols + 2 * rows - 4. Three things fall out of it:

min(d, P - d) is distance the short way round, so an effect crosses the corner it started from instead of stopping at a seam.
(p - head + P) % P is "how far ahead of the head", which makes an arc rotate rather than a blob slide.
sin(TAU * p / P) is that position as an angle, one cycle to the lap — and a sine wraps at the corner for free, where a ramp needs the trick above. Any whole number of lobes (* 3 / P) fits the ring exactly, which is what makes a standing wave stand.

There is no way to name a subexpression, so the formula is written out in full — which is why a small effect is a long line.

Thirteen of them are ready to paste in contrib/chrome: a shine running round the border, a sine comet with softer shoulders, marching ants, a standing wave, drifting sparkles, ripples leaving a corner in both directions, a rotating arc, a bit-drift pattern, a heartbeat, a static gradient, corner glints, a sheen across the title rule and an XOR barcode along it. Its README has the two techniques they share: the angle idiom above, and overdrive then clip (* 14 - 3000 after a sine) to turn a glow into an arc.

A border that says something#

Hung off a state, this is chrome doing the job chrome is for, in no room and no words:

states {
    // a dead pane's frame breathes red until you deal with it
    dead { tint where="chrome" channel="fg" color="#ff0033" amount="abs(t/8%510-255)" }
    // one that has not started yet is outlined, not filled
    suspended { tint where="chrome" channel="fg" color="#8a8a95" amount=160 }
    // and the panes you are not in recede, frame and contents together
    unfocused { dim amount=60; dim where="chrome" channel="fg" amount=90 }
}

since is what makes a flash possible: it is how long the pane has been in this state, where t only knows what time it is. The bell state ends when you look at the pane, because that is what answering a bell is.

A pane that a small terminal has collapsed to a single row is chrome all the way through, which makes this the only kind of pass that can still colour it — and that is the state where a colour is worth the most.

Animation costs a clock#

Anything that reads t or since asks the session to keep painting, at anim_ms (50ms, so 20fps) and only while such a pass is actually on screen. A pulse hung off dead costs a frame clock while a pane is dead and nothing for the rest of the session; the same pass in the global shaders block costs it for the whole session.

anim_ms 0 turns the clock off, which leaves an animated shader advancing only when something else causes a frame.

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