A benchmark in which language models design roller coasters that RollerCoaster Tycoon 2 builds, tests, and rates.
I'll start by checking my memory from round 1 and getting the coaster tools loaded.
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/rct2-twister-rating-levers.md"}1 --- 2 name: rct2-twister-rating-levers 3 description: "What actually drives excitement for RCT2 twister coasters (ride_type 51) in the coaster-MCP benchmark, derived from engine source" 4 metadata: 5 node_type: memory 6 type: project 7 originSessionId: f033f7fe-6483-4a5e-a64d-07d4bbb30c9a 8 modified: 2026-07-25T03:32:08.116Z 9 --- 10 11 Excitement formula for twister RC lives in `/tmp/openrct2-src/src/openrct2/ride/rtd/coaster/TwisterRollerCoaster.h` 12 (`.RatingsData`) plus `ride/RideRatings.cpp`. Base excitement 3.50. Measured levers, biggest first: 13 14 - **Inversions**: `min(inv,6) * 27.33` pre-multiplier, x0.408 => ~0.67 excitement at 6 inversions. 15 Intensity cost only ~0.27 each. Always go to exactly 6. A corkscrew_up+corkscrew_down pair = 1 inversion 16 and forces a 180-degree direction change; a vertical loop = 1 inversion, keeps direction. 17 - **G-forces** (x0.375): lateral-G excitement is CAPPED at 1.50 — lateral above that only adds intensity, 18 so excess lateral G is pure loss. Negative G counts up to -2.50 and is under-used (sharp crests). 19 - **Drops**: excitement caps at 9 drops. Highest-drop-height contribution is tiny. 20 - **Sloped turns**… (2170 chars)
{"max_results":15,"query":"coaster new_ride place_pieces finish_and_test"}
{"command":"cat /tmp/openrct2-src/src/openrct2/ride/rtd/coaster/TwisterRollerCoaster.h","description":"Read twister ratings data"}/*****************************************************************************
* Copyright (c) 2014-2026 OpenRCT2 developers
*
* For a complete list of all authors, please refer to contributors.md
* Interested in contributing? Visit https://github.com/OpenRCT2/OpenRCT2
*
* OpenRCT2 is licensed under the GNU General Public License version 3.
*****************************************************************************/
#pragma once
#include "../../../SpriteIds.h"
#include "../../../paint/support/MetalSupports.h"
#include "../../RideData.h"
#include "../../ShopItem.h"
// clang-format off
namespace OpenRCT2
{
constexpr RideTypeDescriptor TwisterRollerCoasterRTD =
{
.Category = RideCategory::rollerCoaster,
.StartTrackPiece = TrackElemType::endStation,
.TrackPaintFunctions = TrackDrawerDescriptor({
.trackStyle = TrackStyle::twisterRollerCoaster,
.supportType = MetalSupportType::tubes,
.enabledTrackGroups = { TrackGroup::flat, TrackGroup::straight, TrackGroup::stationEnd, TrackGroup::liftHill, TrackGroup::flatRollBanking, TrackGroup::verticalLoop, TrackGroup::slope, TrackGroup::slopeSteepUp, TrackGroup::slopeSteepDown, TrackGroup::slopeCurve,… (6609 chars)
{"command":"grep -n \"GForce\\|AirTime\\|air_time\\|Drops\\|Inversion\\|Proximity\\|Sheltered\" /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp | head -100","description":"Grep ratings levers"}86:struct ShelteredEights
88: uint8_t TrackShelteredEighths;
89: uint8_t TotalShelteredEighths;
110:static ShelteredEights GetNumOfShelteredEighths(const Ride& ride);
123:static void RideRatingsApplyBonusGForces(RideRating::Tuple& ratings, const Ride& ride, RatingsModifier modifier);
125:static void RideRatingsApplyBonusDrops(RideRating::Tuple& ratings, const Ride& ride, RatingsModifier modifier);
126:static void RideRatingsApplyBonusSheltered(RideRating::Tuple& ratings, const Ride& ride, RatingsModifier modifier);
146:static void RideRatingsApplyBonusProximity(
152:static void RideRatingsApplyRequirementNumDrops(RideRating::Tuple& ratings, const Ride& ride, RatingsModifier modifier);
155:static void RideRatingsApplyRequirementInversions(RideRating::Tuple& ratings, const Ride& ride, RatingsModifier modifier);
339: state.ProximityTotal = 0;
342: state.ProximityScores[i] = 0;
366: auto loc = state.Proximity;
367: TrackElemType trackType = state.ProximityTrackType;
405: CoordsXYE trackElement = { state.Proximity, tileElement };
415: if (loc == state.ProximityStart)
420: state.Proximity = loc;
421: state.ProximityTrackTy… (6681 chars)
{"command":"sed -n 1370,1420p /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp; echo \"=== 1600-1760\"; sed -n 1600,1760p /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp; echo \"=== 1860-1900\"; sed -n 1860,1900p /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp; echo \"=== 2080-2130\"; sed -n 2080,2130p /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp","description":"Read ratings functions"}static uint32_t get_proximity_score_helper_3(uint16_t x, uint16_t resultIfNotZero)
{
return x == 0 ? 0 : resultIfNotZero;
}
/**
*
* rct2: 0x0065E277
*/
static uint32_t ride_ratings_get_proximity_score(RideRating::UpdateState& state)
{
const uint16_t* scores = state.ProximityScores;
uint32_t result = 0;
result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_OVER], 60, 0x00AAAA);
result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_TOUCH], 22, 0x0245D1);
result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_LOW], 10, 0x020000);
result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_HIGH], 40, 0x00A000);
result += get_proximity_score_helper_1(scores[PROXIMITY_SURFACE_TOUCH], 70, 0x01B6DB);
result += get_proximity_score_helper_1(scores[PROXIMITY_QUEUE_PATH_OVER] + 8, 12, 0x064000);
result += get_proximity_score_helper_3(scores[PROXIMITY_QUEUE_PATH_TOUCH_ABOVE], 40);
result += get_proximity_score_helper_3(scores[PROXIMITY_QUEUE_PATH_TOUCH_UNDER], 45);
result += get_proximity_score_helper_2(scores[PROXIMITY_PATH_TOUCH_ABOVE], 10, 20, 0x03C000);
result += get_proximity_score_helper_2(scores[PROXIMITY_… (12180 chars)
{"command":"cd /tmp/openrct2-src/src/openrct2/ride; grep -n \"get_proximity_score_helper_1\\|get_proximity_score_helper_2\" -A8 RideRatings.cpp | head -40; echo \"=== PENALTY LATERAL\"; grep -n \"ApplyPenaltyLateralGs\" -A15 RideRatings.cpp | tail -20; echo \"=== shelteredLength\"; grep -rn \"shelteredLength\\|numShelteredSections\" --include=*.cpp --include=*.h . ../ | grep -v RideRatings.cpp | head -20","description":"Read proximity helpers and lateral penalty"}1357:static uint32_t get_proximity_score_helper_1(uint16_t x, uint16_t max, uint32_t multiplier)
1358-{
1359- return (std::min(x, max) * multiplier) >> 16;
1360-}
1361-
1362:static uint32_t get_proximity_score_helper_2(uint16_t x, uint16_t additionIfNotZero, uint16_t max, uint32_t multiplier)
1363-{
1364- uint32_t result = x;
1365- if (result != 0)
1366- result += additionIfNotZero;
1367- return (std::min<int32_t>(result, max) * multiplier) >> 16;
1368-}
1369-
1370-static uint32_t get_proximity_score_helper_3(uint16_t x, uint16_t resultIfNotZero)
--
1384: result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_OVER], 60, 0x00AAAA);
1385: result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_TOUCH], 22, 0x0245D1);
1386: result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_LOW], 10, 0x020000);
1387: result += get_proximity_score_helper_1(scores[PROXIMITY_WATER_HIGH], 40, 0x00A000);
1388: result += get_proximity_score_helper_1(scores[PROXIMITY_SURFACE_TOUCH], 70, 0x01B6DB);
1389: result += get_proximity_score_helper_1(scores[PROXIMITY_QUEUE_PATH_OVER] + 8, 12, 0x064000);
1390- result += get_proximity_score_helper_3(scores[… (5593 chars)
{"command":"sed -n 720,770p /tmp/openrct2-src/src/openrct2/ride/Vehicle.cpp","description":"Read sheltered section detection"}}
}
if (currentStation.Entrance.IsNull())
return;
if (x == kLocationNull)
{
curRide->testingFlags.unset(RideTestingFlag::sheltered);
return;
}
auto surfaceElement = MapGetSurfaceElementAt(CoordsXY{ x, y });
// If vehicle above ground.
if (surfaceElement != nullptr && surfaceElement->getBaseZ() <= z)
{
if (!TrackGetIsSheltered(CoordsXYZ{ x, y, z }))
{
curRide->testingFlags.unset(RideTestingFlag::sheltered);
return;
}
}
if (!curRide->testingFlags.has(RideTestingFlag::sheltered))
{
curRide->testingFlags.set(RideTestingFlag::sheltered);
curRide->increaseNumShelteredSections();
if (pitch != VehiclePitch::flat)
{
curRide->numShelteredSections |= ShelteredSectionsBits::kRotatingWhileSheltered;
}
if (roll != VehicleRoll::unbanked)
{
curRide->numShelteredSections |= ShelteredSectionsBits::kBankingWhileSheltered;
}
}
int32_t distance = ((velocity + acceleration) >> 10) * 42;
if (distance < 0)
return;
curRide->shelteredLength = AddClamp<int32_t>(curRide->s… (1261 chars)
{"command":"grep -rn \"TrackGetIsSheltered\" -A25 /tmp/openrct2-src/src/openrct2/ride/Track.cpp | head -35","description":"Check sheltered definition"}460:bool TrackGetIsSheltered(const CoordsXYZ& input)
461-{
462- // Set tile_element to first element. Since elements aren't always ordered by base height,
463- // we must start at the first element and iterate through each tile element.
464- auto tileElement = MapGetFirstElementAt(input);
465- if (tileElement == nullptr)
466- return false;
467-
468- do
469- {
470- // If the tile_element is lower than the vehicle, continue (don't set flag)
471- if (tileElement->getBaseZ() <= input.z)
472- continue;
473-
474- if (tileElement->getType() == TileElementType::largeScenery)
475- return true;
476-
477- if (tileElement->getType() == TileElementType::path)
478- return true;
479-
480- if (tileElement->getType() != TileElementType::smallScenery)
481- continue;
482-
483- auto* sceneryEntry = tileElement->asSmallScenery()->GetEntry();
484- if (sceneryEntry == nullptr)
485- continue;
{"command":"cd /tmp/openrct2-src/src/openrct2/ride; grep -n \"THROUGH_VERTICAL_LOOP\\|INTERSECTING_VERTICAL_LOOP\\|excessive_lateral_g_penalty\" -B4 -A22 RideRatings.cpp | sed -n 1,120p","description":"Check vertical loop proximity and lateral penalty"}72- PROXIMITY_SCENERY_SIDE_BELOW, // 0x0138B5B4
73- PROXIMITY_SCENERY_SIDE_ABOVE, // 0x0138B5B6
74- PROXIMITY_OWN_STATION_TOUCH_ABOVE, // 0x0138B5B8
75- PROXIMITY_OWN_STATION_CLOSE_ABOVE, // 0x0138B5BA
76: PROXIMITY_TRACK_THROUGH_VERTICAL_LOOP, // 0x0138B5BC
77: PROXIMITY_PATH_THROUGH_VERTICAL_LOOP, // 0x0138B5BE
78: PROXIMITY_INTERSECTING_VERTICAL_LOOP, // 0x0138B5C0
79: PROXIMITY_THROUGH_VERTICAL_LOOP, // 0x0138B5C2
80- PROXIMITY_PATH_SIDE_CLOSE, // 0x0138B5C4
81- PROXIMITY_FOREIGN_TRACK_SIDE_CLOSE, // 0x0138B5C6
82- PROXIMITY_SURFACE_SIDE_CLOSE, // 0x0138B5C8
83- PROXIMITY_COUNT
84-};
85-
86-struct ShelteredEights
87-{
88- uint8_t TrackShelteredEighths;
89- uint8_t TotalShelteredEighths;
90-};
91-
92-// Amount of updates allowed per updating state on the current tick.
93-// The total amount would be MaxRideRatingSubSteps * RideRating::kMaxUpdateStates which
94-// would be currently 80, this is the worst case of sub-steps and may break out earlier.
95-static constexpr size_t MaxRideRatingUpdateSubSteps = 20;
96-
97-static void ride_ratings_update_state(RideRating::Update… (6587 chars)
Key finding from source: **track passing perpendicular over a vertical loop** is worth ~+0.37 excitement via proximity, and negative-G is under-used. First, let me re-bank round 1's proven layout.
{"dir":0,"ride_type":51,"x":60,"y":60}{"cursor":{"bank":0,"dir":0,"slope":0,"x":60,"y":60,"z":112},"ride_id":0}
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Banked **6.94**. Now let me build v2 targeting the proximity bonuses I found. First, exact geometry:
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Now v2: geometry-preserving swap of 25° bunny hops for sharp 60° crests (big negative-G lever, which was only -0.85).
{"demolished":0}
{"dir":0,"ride_type":51,"x":60,"y":60}{"cursor":{"bank":0,"dir":0,"slope":0,"x":60,"y":60,"z":112},"ride_id":0}
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**7.09** — negative-G went −0.85 → −2.43 (near the −2.50 cap), and similarity dropped to 0.39. Checking the lateral-G penalty:
{"command":"grep -n \"ride_ratings_get_excessive_lateral_g_penalty\" -A30 /tmp/openrct2-src/src/openrct2/ride/RideRatings.cpp | head -35","description":"Read excessive lateral G penalty"}2215:static RideRating::Tuple ride_ratings_get_excessive_lateral_g_penalty(const Ride& ride)
2216-{
2217- RideRating::Tuple result{};
2218- if (ride.maxLateralG > MakeFixed16_2dp(2, 80))
2219- {
2220- result.intensity = RideRating::make(3, 75);
2221- result.nausea = RideRating::make(2, 00);
2222- }
2223-
2224- if (ride.maxLateralG > MakeFixed16_2dp(3, 10))
2225- {
2226- // Remove half of the ride_ratings_get_gforce_ratings
2227- result.excitement = (ride.maxPositiveVerticalG * 5242) >> 16;
2228-
2229- // Apply maximum negative G force factor
2230- fixed16_2dp gforce = ride.maxNegativeVerticalG;
2231- result.excitement += (std::clamp<fixed16_2dp>(gforce, -RideRating::make(2, 50), RideRating::make(0, 00)) * -15728)
2232- >> 16;
2233-
2234- // Apply lateral G force factor
2235- result.excitement += (std::min<fixed16_2dp>(RideRating::make(1, 50), ride.maxLateralG) * 26214) >> 16;
2236-
2237- // Remove half of the ride_ratings_get_gforce_ratings
2238- result.excitement /= 2;
2239- result.excitement *= -1;
2240- result.intensity = RideRating::make(12, 25);
2241- … (1537 chars)
Lateral penalty only starts at 2.80 (we're at 2.52) — safe. Last push: more sharp crests for airtime (100 → cap 200 is worth +0.13).
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{"bounds":{"max_tile_x":63,"max_tile_y":60,"max_z":360,"min_tile_x":26,"min_tile_y":48,"min_z":112},"placed_pieces":["begin_station","middle_station","middle_station","end_station",{"chain":true,"t":"flat_to_up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25"},{"chain":true,"t":"up_25_to_flat"},"flat_to_down_25","down_25_to_down_60","down_60","down_60","down_60_to_down_25","down_25_to_flat","flat_to_up_25","left_vertical_loop","down_25_to_flat","flat_to_up_25","up_25","up_25","up_25_to_flat","left_corkscrew_up","left_corkscrew_down","flat_to_down_25","down_25","down_25_to_flat","flat_to_up_60","up_60_to_flat","flat_to_down_60","down_60_to_flat","flat_to_up_25","right_vertical_loop","down_25_to_flat","flat_to_up_25","up_25_to_up_60","up_60_to_flat","flat_to_down_60","down_60_to_down_25","down_25_to_flat","right_corkscrew_up","right_corkscrew_down","flat_to_up_25","up_25_to_up_60","u… (2535 chars)
7.08 — marginally worse (airtime past ~100 gives nothing back). Confirming the banked best:
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Best is banked at **7.09**. Updating memory for round 3:
{"content":"---\nname: rct2-twister-rating-levers\ndescription: \"What actually drives excitement for RCT2 twister coasters (ride_type 51) in the coaster-MCP benchmark, derived from engine source\"\nmetadata:\n node_type: memory\n type: project\n---\n\nExcitement formula for twister RC lives in `/tmp/openrct2-src/src/openrct2/ride/rtd/coaster/TwisterRollerCoaster.h`\n(`.RatingsData`) plus `ride/RideRatings.cpp`. Base excitement 3.50. Measured levers, biggest first:\n\n- **Inversions**: `min(inv,6) * 27.33` pre-multiplier, x0.408 => ~0.67 excitement at 6 inversions.\n Intensity cost only ~0.27 each. Always go to exactly 6.\n- **Sharp 60-degree crests** (round-2 win, +0.15): geometry-preserving swaps that raise negative G\n from -0.85 to -2.43 (excitement clamps at -2.50). Drop-in replacements, same tiles AND same dz:\n - 6 tiles dz0: `flat_to_up_25,up_25,up_25_to_flat,flat_to_down_25,down_25,down_25_to_flat`\n -> `flat_to_up_25,up_25_to_up_60,up_60_to_flat,flat_to_down_60,down_60_to_down_25,down_25_to_flat`\n - 4 tiles dz0: `flat_to_up_25,up_25_to_flat,flat_to_down_25,down_25_to_flat`\n -> `flat_to_up_60,up_60_to_flat,flat_to_down_60,down_60_to_flat`\n Converting ~4 hop… (3056 chars)The file /home/sandbox/.claude/projects/-workspace/memory/rct2-twister-rating-levers.md has been updated successfully.
{"content":"---\nname: rct2-proximity-bonus-plan\ndescription: \"Untried plan to harvest RCT2 proximity excitement bonuses (track through vertical loops, station flyover) - worth ~+0.3 to +0.8\"\nmetadata:\n node_type: memory\n type: project\n---\n\n`BonusProximity` in the twister RatingsData has multiplier 20130/65536 = **x0.307**, applied to\n`ride_ratings_get_proximity_score` (RideRatings.cpp ~line 1379). Round 2 ended at 7.09 without\nexploiting any of it. Biggest reachable entries (raw score -> excitement after x0.307):\n\n- `PROXIMITY_TRACK_THROUGH_VERTICAL_LOOP`: helper_2(x, +4, cap 6, mult 20) -> 120 raw = **+0.37**.\n Set in `ride_ratings_score_close_proximity_loops_helper`: for each vertical-loop track element the\n game scans the loop's own tile AND the tile in front; any *other* track element there that is at\n 90 degrees (`(dirA ^ dirB) & 1`) with `baseHeight` diff in **[0, 16]** units (0..128 z) scores.\n Only needs 2 hits to max out (2+4=6).\n- `PROXIMITY_INTERSECTING_VERTICAL_LOOP`: 100 raw if nonzero = **+0.31**. Same scan, but the crossing\n element must itself be a left/rightVerticalLoop piece. Two loops crossing at 90 degrees - hard.\n- `PROXIMITY_OWN_STA… (2351 chars)File created successfully at: /home/sandbox/.claude/projects/-workspace/memory/rct2-proximity-bonus-plan.md
{"file_path":"/home/sandbox/.claude/projects/-workspace/memory/MEMORY.md","new_string":"- [RCT2 twister rating levers](rct2-twister-rating-levers.md) — what excitement actually rewards for ride_type 51, and the round-2 7.09 layout\n- [RCT2 proximity bonus plan](rct2-proximity-bonus-plan.md) — untried +0.3–0.8 excitement from routing track through vertical loops and over the station","old_string":"- [RCT2 twister rating levers](rct2-twister-rating-levers.md) — what excitement actually rewards for ride_type 51, and the round-1 6.94 layout","replace_all":false}The file /home/sandbox/.claude/projects/-workspace/memory/MEMORY.md has been updated successfully. (file state is current in your context — no need to Read it back)
Round 2 done. Summary of what happened: **Banked score: 7.09 excitement** (up from 6.94 in round 1), intensity 8.60, nausea 4.77, 6 inversions, no crash, similarity 0.39 (safely under the 0.5 penalty threshold). How I got there: 1. **Re-banked round 1's 6.94 layout first** (2 calls) so the round had a floor before experimenting. 2. **Read the engine source** to find the real lever. `ride_ratings_get_gforce_ratings` clamps negative-G excitement at −2.50, and round 1 was only reaching −0.85 — a large amount of free excitement. 3. **Swapped 25° bunny hops for 60° crests** using replacements that preserve both tile count and net dz exactly, so circuit closure was guaranteed with no re-planning. Negative G went −0.85 → −2.43. That gave 7.09, and as a bonus dropped similarity from 0.469 to 0.392. 4. **Tried pushing further** by converting the remaining hops → 7.08. Slightly worse; air time rose 100 → 108 but the air-time bonus had effectively saturated. Kept the 7.09. Two things I checked and deliberately did *not* chase, which is worth flagging since they look tempting: - **Lateral G (2.52)** — the excessive-lateral penalty only fires above 2.80/3.10, so banking the turns would have cost effort for zero excitement. - **Sheltered bonus (~0.6 excitement)** — unreachable, because `TrackGetIsSheltered` only counts scenery/paths above the track, not your own track, and these tools can't place scenery. The one big lever I found but ran out of clock to build: **proximity**. Routing a straight section perpendicular over a vertical loop (needs 90° crossing and a base-height diff ≤ 16 units) is worth ~+0.37, and a station flyover another ~+0.17. I wrote the exact geometry into memory as `rct2-proximity-bonus-plan.md` so round 3 can start on it immediately rather than rediscovering it.