MOHAWK: RIVEN: Generate dome code as in original game #5470
Conversation
In the original game, the dome combination is not completely random; only the first number is one that can be seen in the school (range 2-10), two numbers are chosen from the range 11-15, and two are chosen from the range 16-24. Presumably, this is done so that the code has approximately equal difficulty for every game. Until now, scummvm has generated completely random codes, which results in some games having very easy codes (when most of the numbers are below 10). Also, there's a 20% chance that the last number is 25, which is never used in the original game.
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Nice work |
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I love this, and I don't even know Riven. Reverse engineering with AutoHotkey and graphs is just as legitimate as disassembly, arguably much more fun, and produces better visuals. This is a beautiful PR and excellently written. How do we trick you into doing more? |
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@vholten : This change looks reasonable and self-contained. It is certainly closer to the original than the existing algorithm, if it is not perfectly correct. If someone or yourself wishes to check this against the original assembly later and make any minor adjustments, then merging this does not preclude that. Thank you for your contribution. Merging as-is. |
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Thanks everyone for the nice and motivating comments.
No tricks necessary! I'm currently looking into a sound-related issue in Zork: Grand Inquisitor (zvision engine). This may or may not be a bug, I'll need to do some more analysis. |
This pull request updates the code that randomizes the combination for the domes, so that the generated combinations correspond to those in the original game.
In the original game, the dome combination is not completely random; only the first number is one that can be learned in the school (range 2–10), the next two numbers are chosen from the range 11–15, and the last two numbers are chosen from the range 16–24. Presumably, this was done so that the code has approximately equal difficulty for every game.
Until now, ScummVM has generated completely random codes, which results in some games having very easy codes (when most of the numbers are below 10). Also, there's a 20% chance that the last number is 25, which never occurs in the original game's dome combinations.
Graphical summary of possible values for each position in the combination:
Research
To find the original game's dome combinations, I played the game from an old Riven executable (version 1.02). I made a script with AutoHotkey that creates a new game and saves it, and does this 2000 times. I then extracted the dome combination from each saved game. I analyzed the list of the 2000 combinations to find the possible numbers for each position, as well as how often these occur. The code in this pull request generates numbers with the same probability distribution as in the original game.
Distributions of the five digits in the 2000 combinations generated in the original game
Further confirmation can be found in old let's play videos or old websites where people posted their dome codes (from when the scummvm implementation did not yet exist). They correspond to the allowed possibilities mentioned above.