From 755951607d0bd89abdc410d12c0ca4d3a635aed2 Mon Sep 17 00:00:00 2001
From: zk <zkldi@proton.me>
Date: Wed, 17 Jun 2026 23:29:59 +0100
Subject: [PATCH] fix: fucking finally fix delta cells (#1683)

---
 typescript/client/src/lib/games/bms-pms.tsx | 18 ++++--------
 typescript/client/src/lib/games/iidx.tsx    | 16 +++--------
 typescript/common/src/utils/util.ts         | 32 ++++++++++++++++++++-
 3 files changed, 40 insertions(+), 26 deletions(-)

diff --git a/typescript/client/src/lib/games/bms-pms.tsx b/typescript/client/src/lib/games/bms-pms.tsx
index 2e2d6d56e..95142c754 100644
--- a/typescript/client/src/lib/games/bms-pms.tsx
+++ b/typescript/client/src/lib/games/bms-pms.tsx
@@ -6,7 +6,7 @@ import { GetEnumColour } from "#lib/game-implementations";
 import { type GameClientImplementation } from "#lib/types";
 import { IsNullish } from "#util/misc";
 import { NumericSOV } from "#util/sorts";
-import { COLOUR_SET, type GamesForGroup, IIDXLIKE_GBOUNDARIES } from "tachi-common";
+import { COLOUR_SET, type GamesForGroup, RawIIDXGradeBoundaries } from "tachi-common";
 import { FormatSieglindeBMS } from "tachi-common/config/game-support/bms";
 
 import { bgc, CreateRatingSys } from "./_util";
@@ -67,7 +67,7 @@ const BASE_IMPL: GameClientImplementation<GamesForGroup["bms" | "pms"]> = {
 		["Deltas", "Deltas", NumericSOV((x) => x.scoreData.percent)],
 		["Lamp", "Lamp", NumericSOV((x) => x.scoreData.enumIndexes.lamp)],
 	],
-	scoreCoreCells: ({ sc }) => (
+	scoreCoreCells: ({ sc, chart }) => (
 		<>
 			<ScoreCell
 				colour={GetEnumColour(sc, "grade")}
@@ -76,18 +76,10 @@ const BASE_IMPL: GameClientImplementation<GamesForGroup["bms" | "pms"]> = {
 				score={sc.scoreData.score}
 			/>
 			<DeltaCell
-				formatNumFn={(deltaPercent) => {
-					const max = Math.floor(sc.scoreData.score / (sc.scoreData.percent / 100));
-
-					const v = (deltaPercent / 100) * max;
-
-					// i don't know if this is correct
-					// it's just really hard to work out.
-					return Math.round(v).toFixed(0);
-				}}
+				formatNumFn={(n) => Math.floor(n / 18).toString()}
 				grade={sc.scoreData.grade}
-				gradeBoundaries={IIDXLIKE_GBOUNDARIES}
-				value={sc.scoreData.percent}
+				gradeBoundaries={RawIIDXGradeBoundaries(chart.data.notecount)}
+				value={sc.scoreData.score * 18}
 			/>
 			<BMSOrPMSLampCell score={sc} />
 		</>
diff --git a/typescript/client/src/lib/games/iidx.tsx b/typescript/client/src/lib/games/iidx.tsx
index 63a48a2b8..851d10e14 100644
--- a/typescript/client/src/lib/games/iidx.tsx
+++ b/typescript/client/src/lib/games/iidx.tsx
@@ -7,7 +7,7 @@ import { GetEnumColour } from "#lib/game-implementations";
 import { type GameClientImplementation } from "#lib/types";
 import { ChangeOpacity } from "#util/color-opacity";
 import { NumericSOV } from "#util/sorts";
-import { COLOUR_SET, type GamesForGroup, IIDX_LAMPS, IIDXLIKE_GBOUNDARIES } from "tachi-common";
+import { COLOUR_SET, type GamesForGroup, IIDX_LAMPS, RawIIDXGradeBoundaries } from "tachi-common";
 
 import { bgc, CreateRatingSys } from "./_util";
 
@@ -97,18 +97,10 @@ const IIDXCoreCells: GameClientImplementation<GamesForGroup["iidx"]>["scoreCoreC
 			score={sc.scoreData.score}
 		/>
 		<DeltaCell
-			formatNumFn={(deltaPercent) => {
-				const max = Math.floor(sc.scoreData.score / (sc.scoreData.percent / 100));
-
-				const v = (deltaPercent / 100) * max;
-
-				// i don't know if this is correct
-				// it's just really hard to work out.
-				return Math.round(v).toFixed(0);
-			}}
+			formatNumFn={(n) => Math.floor(n / 18).toString()}
 			grade={sc.scoreData.grade}
-			gradeBoundaries={IIDXLIKE_GBOUNDARIES}
-			value={sc.scoreData.percent}
+			gradeBoundaries={RawIIDXGradeBoundaries(chart.data.notecount)}
+			value={sc.scoreData.score * 18}
 		/>
 		<IIDXLampCell chart={chart} sc={sc} />
 	</>
diff --git a/typescript/common/src/utils/util.ts b/typescript/common/src/utils/util.ts
index 1339b2d9d..d0891888a 100644
--- a/typescript/common/src/utils/util.ts
+++ b/typescript/common/src/utils/util.ts
@@ -1,7 +1,6 @@
 import type { PrudenceError, ValidSchemaValue } from "prudence";
 import type { ZodObject } from "zod";
 
-import type { GradeBoundary, IIDXLikes } from "../constants/grade-boundaries";
 import type {
 	BMSCourseDocument,
 	BMSGames,
@@ -22,6 +21,11 @@ import type {
 } from "../types/metrics";
 
 import { ALL_GAMES, GameToGameGroup, GetGameConfig, GetGameGroupConfig } from "../config/config";
+import {
+	type GradeBoundary,
+	type IIDXLikes,
+	MakeGradeBoundaries,
+} from "../constants/grade-boundaries";
 
 /**
  * Stick this in the "default" branch of switch exprs to statically typecheck that your
@@ -454,6 +458,32 @@ export function IIDXLikeGetGrade(
 	return "F";
 }
 
+/**
+ * Computes exact integer EX-score grade boundaries for a given IIDX-like notecount.
+ *
+ * These mirror the integer arithmetic in IIDXLikeGetGrade and avoid the
+ * floating-point rounding errors that arise from working through percent-space
+ * when the grade denominators are ninths (or eighteenths for MAX-).
+ */
+export function RawIIDXGradeBoundaries(
+	notecount: integer,
+): Array<GradeBoundary<GetEnumValue<IIDXLikes, "grade">>> {
+	const max = notecount * 2;
+
+	return MakeGradeBoundaries<GetEnumValue<IIDXLikes, "grade">>({
+		F: 0,
+		E: max * 4,
+		D: max * 6,
+		C: max * 8,
+		B: max * 10,
+		A: max * 12,
+		AA: max * 14,
+		AAA: max * 16,
+		"MAX-": max * 17,
+		MAX: max * 18,
+	});
+}
+
 export function EnumIndexToValue<
 	TGame extends V3Game,
 	EV extends ExtractEnumMetricNames<AllConfMetrics[TGame]>,