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fix: tutorial scrollymation racing global smooth-scroll CSS #77

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Merged
EDRipper merged 1 commit into from
Jul 31, 2026
Merged

fix: tutorial scrollymation racing global smooth-scroll CSS #77

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18 changes: 7 additions & 11 deletions frontend/src/routes/tutorial/+page.svelte
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Original file line number Diff line number Diff line change
Expand Up @@ -117,21 +117,21 @@
// Start one section below landing, animate scroll up to landing
const landingPos = skyEl!.offsetTop + skyEl!.offsetHeight - innerHeight * 2;
const startPos = landingPos + innerHeight;
window.scrollTo(0, startPos);
window.scrollTo({ top: startPos, behavior: 'instant' });
await tick();
const duration = 2400;
const startTime = performance.now();
function animateScroll(now: number) {
const t = Math.min((now - startTime) / duration, 1);
const ease = t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2;
window.scrollTo(0, startPos + (landingPos - startPos) * ease);
window.scrollTo({ top: startPos + (landingPos - startPos) * ease, behavior: 'instant' });
if (t < 1) {
requestAnimationFrame(animateScroll);
} else {
locked = true;
tick().then(() => {
if (skyEl) {
window.scrollTo(0, skyEl.offsetTop + skyEl.offsetHeight - innerHeight * 2);
window.scrollTo({ top: skyEl.offsetTop + skyEl.offsetHeight - innerHeight * 2, behavior: 'instant' });
}
});
}
Expand All @@ -141,19 +141,15 @@

// Prevent scrolling past the bottom back into the scrollymation
$effect(() => {
// Depend on scrollY so this reruns on scroll, but read window.scrollY for
// the actual value: the scrollY binding lags the native scroll event, so
// right when `locked` flips true it can still read stale (near-zero) and
// clamp us up to `top` before the real position is ever reflected.
void scrollY;
if (locked && skyEl) {
const top = skyEl.offsetTop + innerHeight;
const bottom = skyEl.offsetTop + skyEl.offsetHeight - innerHeight;
const current = window.scrollY;
if (current < top) {
window.scrollTo(0, top);
window.scrollTo({ top, behavior: 'instant' });
} else if (current > bottom) {
window.scrollTo(0, bottom);
window.scrollTo({ top: bottom, behavior: 'instant' });
}
}
});
Expand Down Expand Up @@ -254,12 +250,12 @@
locked = true;
tick().then(() => {
if (skyEl) {
window.scrollTo(0, skyEl.offsetTop + sectionMultipliers[data.stage!] * innerHeight);
window.scrollTo({ top: skyEl.offsetTop + sectionMultipliers[data.stage!] * innerHeight, behavior: 'instant' });
}
});
} else {
// Auto-play the intro animation
window.scrollTo(0, 0);
window.scrollTo({ top: 0, behavior: 'instant' });
setTimeout(startIntroAnimation, 500);
}

Expand Down
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