alexion
6081e3e325
Imported as a linear vendor commit so forge rebases do not replay the upstream root tree. git-subtree-dir: third_party/pi git-subtree-split: 71023aec1546d6d677a65669c5665c0927ce0dd0
83 lines
2.8 KiB
TypeScript
83 lines
2.8 KiB
TypeScript
/** Lines moved per mouse-wheel event, or `"auto"` to accelerate fast wheel spins. */
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export type WheelScrollLines = number | "auto";
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// Several events closer than this belong to one physical notch (Ghostty emits them ~4 ms apart)
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// or come from a high-resolution source. They move one line each and do not accelerate.
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const BURST_GAP_MS = 5;
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// A pause longer than this ends a scroll gesture.
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const GESTURE_GAP_MS = 200;
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// Average event gap that maps to one line per event. Faster events scale up proportionally.
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const REFERENCE_GAP_MS = 100;
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const MAX_AUTO_LINES = 6;
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/**
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* Local macOS terminals receive wheel and trackpad deltas that the OS has already accelerated,
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* and they emit one event per line. Other platforms, and SSH sessions where the client platform
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* is unknown, usually send one event per wheel notch.
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*/
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function terminalAcceleratesWheel(): boolean {
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const env = process.env;
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return (
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process.platform === "darwin" &&
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env.SSH_CONNECTION === undefined &&
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env.SSH_CLIENT === undefined &&
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env.SSH_TTY === undefined
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);
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}
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/**
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* Converts wheel events into line counts.
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*
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* In `"auto"` mode on terminals that do not accelerate wheel input, the count follows event
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* velocity: an isolated notch moves one line, while a fast spin moves up to six lines per event.
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* For example, notches 100 ms apart move 1 line each, 50 ms apart move 2, and 20 ms apart move 5.
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*/
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export class WheelScrollAccelerator {
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private lines: WheelScrollLines;
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private readonly accelerate: boolean;
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private lastTime = Number.NEGATIVE_INFINITY;
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private lastDirection = 0;
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private averageGap: number | undefined;
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private carry = 0;
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constructor(lines: WheelScrollLines = "auto", accelerate = !terminalAcceleratesWheel()) {
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this.lines = lines;
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this.accelerate = accelerate;
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}
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setLines(lines: WheelScrollLines): void {
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this.lines = lines;
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this.reset();
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}
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/** Return the positive line count for a wheel event in `direction` at time `now` (milliseconds). */
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next(direction: -1 | 1, now: number): number {
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if (this.lines !== "auto") return Number.isFinite(this.lines) ? Math.max(1, Math.floor(this.lines)) : 1;
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if (!this.accelerate) return 1;
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const gap = now - this.lastTime;
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const sameGesture = direction === this.lastDirection && gap <= GESTURE_GAP_MS;
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this.lastTime = now;
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this.lastDirection = direction;
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if (!sameGesture) {
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this.averageGap = undefined;
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this.carry = 0;
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return 1;
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}
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if (gap < BURST_GAP_MS) return 1;
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this.averageGap = this.averageGap === undefined ? gap : (this.averageGap + gap) / 2;
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const lines = Math.min(MAX_AUTO_LINES, Math.max(1, REFERENCE_GAP_MS / this.averageGap)) + this.carry;
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const whole = Math.floor(lines);
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this.carry = lines - whole;
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return whole;
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}
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private reset(): void {
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this.lastTime = Number.NEGATIVE_INFINITY;
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this.lastDirection = 0;
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this.averageGap = undefined;
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this.carry = 0;
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}
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}
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