From 3e2153b39c60bfc2c40093f21949516a2174623b Mon Sep 17 00:00:00 2001
From: Branden J Brown <zephyrtronium@gmail.com>
Date: Fri, 22 May 2026 23:52:21 -0400
Subject: [PATCH] zenno/lib: rearrange parameters in race.speedGain

---
 zenno/src/lib/race.ts                   | 14 +++++++-------
 zenno/src/routes/mspeed/+page.svelte    | 10 +++++-----
 zenno/src/routes/mspeed/SpeedDur.svelte |  2 +-
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/zenno/src/lib/race.ts b/zenno/src/lib/race.ts
index 969b3cb..d5f0793 100644
--- a/zenno/src/lib/race.ts
+++ b/zenno/src/lib/race.ts
@@ -270,24 +270,24 @@ export function skillDuration(baseDur: number, raceLen: number): number {
  * Calculate the distance gained from a target speed boost, including
  * acceleration to the boosted target speed and deceleration back to baseline.
  * @param speedBonus Difference between baseline and boosted speed in m/s
- * @param accel Current acceleration value in m/s²
- * @param decel Current phase-based deceleration value in m/s², a negative value.
+ * @param accel Current acceleration value in m/s², or null for instant acceleration
+ * @param decel Current phase-based deceleration value in m/s², a negative value; or null for instant deceleration
  * @param dur Duration of the boosted speed
  * @returns Distance gained from the speed boost in m
  */
-export function speedGain(speedBonus: number, accel: number, decel: number, dur: number): number {
+export function speedGain(speedBonus: number, dur: number, accel: number | null, decel: number | null): number {
 	// Actual effect of a target speed bonus looks like
 	// 	speed: __/-----\__
 	// 	bonus:   ======
 	// I.e., the speed bonus duration includes acceleration to the new speed
 	// and does not include the acceleration back to baseline after it ends.
-	const accelTime = speedBonus / accel;
-	const decelTime = -speedBonus / decel;
+	const accelTime = accel !== null ? speedBonus / accel : 0;
+	const decelTime = decel !== null ? -speedBonus / decel : 0;
 	if (accelTime >= dur) {
 		// Acceleration is so low that the horse won't reach the boosted target
 		// speed before the effect ends. E.g., G surface aptitude.
-		const peakSpeed = accel * dur;
-		return 0.5 * (peakSpeed * dur - peakSpeed / decel);
+		const peakSpeed = (accel ?? 0) * dur;
+		return 0.5 * (peakSpeed * dur - peakSpeed / (decel ?? 0));
 	}
 	// speedBonus*(dur-accelTime) + speedBonus*accelTime/2 + speedBonus*decelTime/2
 	return speedBonus * (dur + 0.5 * (decelTime - accelTime));
diff --git a/zenno/src/routes/mspeed/+page.svelte b/zenno/src/routes/mspeed/+page.svelte
index f936dee..61c277a 100644
--- a/zenno/src/routes/mspeed/+page.svelte
+++ b/zenno/src/routes/mspeed/+page.svelte
@@ -54,24 +54,24 @@
 	const ssY: Array<ComputedSeries | null> = $derived([
 		{
 			label: 'Aptitude S',
-			y: (x) => speedGain(spotStruggleSpeed(x), accel[0], decel[0], spotStruggleDuration(x, AptitudeLevel.S)) / HORSE_LENGTH,
+			y: (x) => speedGain(spotStruggleSpeed(x), spotStruggleDuration(x, AptitudeLevel.S), accel[0], decel[0]) / HORSE_LENGTH,
 		},
 		{
 			label: 'Aptitude A',
-			y: (x) => speedGain(spotStruggleSpeed(x), accel[0], decel[0], spotStruggleDuration(x, AptitudeLevel.A)) / HORSE_LENGTH,
+			y: (x) => speedGain(spotStruggleSpeed(x), spotStruggleDuration(x, AptitudeLevel.A), accel[0], decel[0]) / HORSE_LENGTH,
 		},
 		frontApt < AptitudeLevel.A
 			? {
 					label: `Aptitude ${AptitudeLevel[frontApt]}`,
-					y: (x) => speedGain(spotStruggleSpeed(x), accel[0], decel[0], spotStruggleDuration(x, frontApt)) / HORSE_LENGTH,
+					y: (x) => speedGain(spotStruggleSpeed(x), spotStruggleDuration(x, frontApt), accel[0], decel[0]) / HORSE_LENGTH,
 				}
 			: null,
 	]);
 	const lcY: Array<ComputedSeries | null> = $derived([
-		{ label: 'Ideal Lane Combo', y: (x) => speedGain(moveLaneModifier(x), accel[0], decel[0], lcDur) / HORSE_LENGTH },
+		{ label: 'Ideal Lane Combo', y: (x) => speedGain(moveLaneModifier(x), lcDur, accel[0], decel[0]) / HORSE_LENGTH },
 	]);
 	const yRule: HorizontalRule[] = $derived([
-		{ y: speedGain(0.35, accel[1], decel[1], skillDuration(2.4, raceLen)) / HORSE_LENGTH, label: 'Professor of Curvature' },
+		{ y: speedGain(0.35, skillDuration(2.4, raceLen), accel[1], decel[1]) / HORSE_LENGTH, label: 'Professor of Curvature' },
 	]);
 </script>
 
diff --git a/zenno/src/routes/mspeed/SpeedDur.svelte b/zenno/src/routes/mspeed/SpeedDur.svelte
index 4312b75..a8e2e4f 100644
--- a/zenno/src/routes/mspeed/SpeedDur.svelte
+++ b/zenno/src/routes/mspeed/SpeedDur.svelte
@@ -17,7 +17,7 @@
 	const { children, speed, dur, accel, decel }: Props = $props();
 	const decels = $derived([decel].flat(1));
 
-	const gain = $derived(decels.map((d) => speedGain(speed, accel, d, dur) / HORSE_LENGTH));
+	const gain = $derived(decels.map((d) => speedGain(speed, dur, accel, d) / HORSE_LENGTH));
 	const text = $derived(gain.map(fmtp).join(' – '));
 </script>