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import type { ScalarAnimationKey } from "@/animation/types";
const BEZIER_SOLVE_ITERATIONS = 20;
export function getBezierPoint({
progress,
p0,
p1,
p2,
p3,
}: {
progress: number;
p0: number;
p1: number;
p2: number;
p3: number;
}) {
const mt = 1 - progress;
return (
mt * mt * mt * p0 +
3 * mt * mt * progress * p1 +
3 * mt * progress * progress * p2 +
progress * progress * progress * p3
);
}
export function getDefaultRightHandle({
leftKey,
rightKey,
}: {
leftKey: ScalarAnimationKey;
rightKey: ScalarAnimationKey;
}) {
const span = rightKey.time - leftKey.time;
const valueDelta = rightKey.value - leftKey.value;
return {
dt: span / 3,
dv: valueDelta / 3,
};
}
export function getDefaultLeftHandle({
leftKey,
rightKey,
}: {
leftKey: ScalarAnimationKey;
rightKey: ScalarAnimationKey;
}) {
const span = rightKey.time - leftKey.time;
const valueDelta = rightKey.value - leftKey.value;
return {
dt: -span / 3,
dv: -valueDelta / 3,
};
}
export function solveBezierProgressForTime({
time,
leftKey,
rightKey,
}: {
time: number;
leftKey: ScalarAnimationKey;
rightKey: ScalarAnimationKey;
}) {
let lower = 0;
let upper = 1;
const rightHandle =
leftKey.rightHandle ?? getDefaultRightHandle({ leftKey, rightKey });
const leftHandle =
rightKey.leftHandle ?? getDefaultLeftHandle({ leftKey, rightKey });
for (let iteration = 0; iteration < BEZIER_SOLVE_ITERATIONS; iteration++) {
const mid = (lower + upper) / 2;
const estimate = getBezierPoint({
progress: mid,
p0: leftKey.time,
p1: leftKey.time + rightHandle.dt,
p2: rightKey.time + leftHandle.dt,
p3: rightKey.time,
});
if (estimate < time) {
lower = mid;
} else {
upper = mid;
}
}
return (lower + upper) / 2;
}
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