Free money exploit with level-to-steep elements of hypercoasters

[James103]

OS: Win 10
Version: 0.2.6, 0.3.0
Commit/Build: 6c3c857, 135cc10

Building a level to steep element of a hypercoaster costs $0.50 less than demolishing it, causing you to gain $0.50 every time you build and delete such an element on level ground.

• Reproducible in RCT2 (vanilla)? No
• Specific to multiplayer? No

Steps to reproduce:

1. Start a hypercoaster.
2. Build a station.
3. Build a level to steep element.
4. Demolish the level to steep element.
5. You've just made $0.50!

Save game:
Test Park.zip

[e-foley]

This issue does not appear to be present in vanilla. Here's what I've found.

Action on level-to-steep-up piece at ground level	RCT2	OpenRCT2
Cost to place	$309.00	$308.50
Sale price	$309.00	$309.00

Even though the piece costs $308.50 in OpenRCT2, it still displays the price in the construction window as "$309".

[James103]

Does this occur with any of the other track types, or is it just the hypercoaster?

[TusharSariya]

How would I go about debugging this? what tools or tutorials should I use?

[duncanspumpkin]

The fact the prices are so similar suggests that this is due to doing refund calculations in a slightly different way to price calculations. You would need to look at the two game actions and see how they differ.

[duncanspumpkin]

Track Remove

        money32 price = RideTrackCosts[ride->type].track_price;
        if (ride_type_has_flag(ride->type, RIDE_TYPE_FLAG_FLAT_RIDE))
        {
            price *= FlatRideTrackPricing[trackType];
        }
        else
        {
            price *= TrackPricing[trackType];
        }
        price >>= 16;
        price = (price + cost) / 2;
        if (ride->lifecycle_flags & RIDE_LIFECYCLE_EVER_BEEN_OPENED)
            price *= -7;
        else
            price *= -10;

        res->Cost = price;

TrackPlace

        money32 price = RideTrackCosts[ride->type].track_price;
        price *= (rideTypeFlags & RIDE_TYPE_FLAG_FLAT_RIDE) ? FlatRideTrackPricing[_trackType] : TrackPricing[_trackType];

        price >>= 16;
        res->Cost = cost + ((price / 2) * 10);

Notice that track place and track remove are using slightly different calcs cost (removal of scenery and supports) in the remove is going to be 5 times greater before the ride is opened! I would need to check the original to work out which one is correct or if its being broken since vanilla.

[duncanspumpkin]

After checking the original the TrackPlace is incorrect.

ebx is the cost. eax is the price. It clearly adds together the cost and the price prior to the divide and multiply.

TrackRemove for reference:

ebp is the cost. eax is the price. It clearly adds together prior to the divide and multiply.

[duncanspumpkin]

This bug has been in the code base a while...

[James103]

In OpenRCT2 0.2.6 release (6c3c857), by building a level-to-steep element of any of the following coaster types and demolishing it, you lose $0.50 ($353 to build, $352 refund).

• Hyper twister coaster
• Giga coaster
• Twister roller coaster

[caseyjohnsonwv]

The profit exploit is also available for Hypercoaster station pieces at heights ending in 5. Placing and removing station pieces at 5ft, 15ft, 25ft, etc profits $0.50, but not at 0ft, 10ft, 20ft, etc. Station pieces are priced the same as flat-to-60s in TrackData.cpp. Corkscrew coaster stations do this too, as do Looping coasters. I have no idea how far this issue goes.

Flat-to-60-up and 60-down-to-flat (hill bottoms) both seem to do this for all heights, but 60-up-to-flat and flat-to-60-down (hill tops) never seem to do it.

Changing TrackPrice in CorkscrewRollerCoaster.h from 105 to 104 makes all corkscrew/hypercoaster cases yield -$0.50 instead of profiting while all correctly-priced ride elements seem unchanged. This isn't the "right" solution, but it's a start. I'll see if I can make any inroads.