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import { clampDb } from "./audio-state";
import { VOLUME_DB_MAX, VOLUME_DB_MIN } from "./audio-constants";
const SLIDER_CURVE_EXPONENT = 2;
const MIN_DISPLAY_DB = -40;
const WAVEFORM_BAR_EXPONENT = 1.5;
const MIN_LINEAR_GAIN = 10 ** (VOLUME_DB_MIN / 20);
const MAX_LINEAR_GAIN = 10 ** (VOLUME_DB_MAX / 20);
const LINEAR_GAIN_RANGE = MAX_LINEAR_GAIN - MIN_LINEAR_GAIN;
function getNormalizedGainFromDb({ db }: { db: number }): number {
const clampedDb = clampDb(db);
const linearGain = 10 ** (clampedDb / 20);
return (linearGain - MIN_LINEAR_GAIN) / LINEAR_GAIN_RANGE;
}
/**
* Maps the clip's volume setting to the line position. The curve is defined in
* linear gain space so dragging near 0 dB is precise while mute compresses into
* the bottom of the clip.
*/
export function getLinePosFromDb({ db }: { db: number }): number {
const normalizedGain = Math.max(
0,
Math.min(1, getNormalizedGainFromDb({ db })),
);
const progress = normalizedGain ** (1 / SLIDER_CURVE_EXPONENT);
return (1 - progress) * 100;
}
/**
* Inverse of getLinePosFromDb. Converts a drag position back into the clip's
* volume setting without depending on the underlying audio content.
*/
export function getDbFromLinePos({ percent }: { percent: number }): number {
const clampedPercent = Math.max(0, Math.min(100, percent));
const progress = 1 - clampedPercent / 100;
const normalizedGain = progress ** SLIDER_CURVE_EXPONENT;
const linearGain = MIN_LINEAR_GAIN + normalizedGain * LINEAR_GAIN_RANGE;
return clampDb(20 * Math.log10(linearGain));
}
/**
* Maps an output amplitude (raw sample amplitude × gain) to a visible waveform
* height fraction using a dB scale. Agnostic to whether the input is peak or
* RMS — the caller decides which measure feeds this function; the mapping
* curve is the same either way.
*
* The log scale keeps quiet content visible while reserving the top of the
* element for amplitudes that approach 0 dBFS.
*/
export function getBarFractionFromOutputAmplitude({
outputAmplitude,
}: {
outputAmplitude: number;
}): number {
if (outputAmplitude <= 0) return 0;
const db = 20 * Math.log10(outputAmplitude);
if (db <= MIN_DISPLAY_DB) return 0;
return Math.min(
1,
((db - MIN_DISPLAY_DB) / -MIN_DISPLAY_DB) ** WAVEFORM_BAR_EXPONENT,
);
}
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