Spyro: Year of the Dragon Decompilation

A decompilation project for the third game in the Spyro the Dragon series, Spyro: Year of the Dragon.

This project aims to produce code that will build to an executable which byte-for-byte matches the one used in the final game. The earliest final version was selected for this project, but additional work to support changes made in the later versions may be supported in the future. Human understanding of the game's code is a primary goal of this project.

Version Info

The earliest release build of the game is used in this project:

• Region: NTSC-U
• Revision: 0
• Primary volume descriptor date: Sep 14th, 2000
• Product code: SCUS-94467

This version contains modchip protection, anti-crack protection, and encrypted overlays.

Project Structure

• asm/: disassembly for non-matching code, and code originally written in assembly.
• include/: include headers for source code, and headers used by disassembly tools.
• progress/: markdown files indicating the current state of the executable and each overlay, for generating the progress tables.
• src/: decompiled source code.
• tools/: contains utilities for building the game.

Matching Progress

Last updated: 2026-10-18

	EXE	Overlays	Total
Total C functions matching	180/337	179/3098	359/3435
Progress percentage	53.41%	5.78%	10.45%

Note: the percentages given above are not necessarily representative of a linear indicator of progress. In particular, many overlay functions repeat and will be easier to implement on the whole than the EXE's functions, and these percentages don't give a picture of how many variables and functions are labelled or understood.

Full Status

Hashes listed are for the final overlays, after correcting checksums and encrypting as necessary:

EXE / Overlay	Expected SHA-256	C functions matching	Progess %
EXE	CB819EE78C556D403779309859CB08A7111331F624759BC1BC380946261BB26E	180/337	53.41%
credits	BBE3F8DEB18E0F462C5918C8AFEDB03A32FE855CC6778E9B8D7E4E3849988BCD	1/5	20.00%
loading	0E94063F258479586AE630C23260B77014BE18BAC5891FBB9A894156B5763AE2	2/16	12.50%
title	675044820F58E521AE2F5AE67F3D050BA37D604D4F06FEC20DCD8806FD1B90F9	2/22	9.09%
atlas	E8F8E69BE901F426D1A8895DDF5842794B73E939B49A09BF9F6ABD9B42E04B11	0/32	0.00%
options	D9644E60000A0D0CC02AF4EE2B5DC4F471EA9CDE57901009A580086CF0CA78AE	2/13	15.38%
level_10	B8C482FB6AA359D9CDD7A03EA487EB0CE3C05B44E0C2DC3D43DBA73F8B493310	7/60	11.67%
level_11	FA11603F49DE1A78FA6E84111E8237F869831C37C9FC2E8F44C857693CFEB9C5	5/80	6.25%
level_12	DA9CEB152622FF2A19C58A8B190146CBBB98BABB35049A6C1E6BFB7AC3CF906E	2/57	3.51%
level_13	D8AC8A0CDA88EA800AE36B864F5910F7139C32EB106E3389F89F15A9B284EC4D	4/65	6.15%
level_14	9F81762F5E71D8F880EE5951C8A17F4A3BEC13E968D72180389CE41F4B76526E	3/82	3.66%
level_15	5895A1A44A3DB1D7BEFD56E3BE3C2F91AF7F6DB0A45BAE10C81A61ECDDBD5461	2/62	3.23%
level_16	9C6B068EF258114F26309973E31CB92987A2126AD5595FFFBBEB281B3F2E6B79	2/47	4.26%
level_17	0052CB2656E28E1D9F501C8DC6540929BC30D3F8726E04D38850C18BFE2DC07D	5/33	15.15%
level_18	CB4D4DB57A656F41C1F6586966BD03B0543E0022D950C8A739B188D85984FD29	2/64	3.12%
level_20	5812CCA80F1F8233F5E805E26F3D90B67F7A12F359911CF8362DEBEE3BB58FFD	1/64	1.56%
level_21	5FB0343DFECF5A1A7DB3B72785DA92C8F1981765E73CAB014E37FD3D4A93E05E	1/61	1.64%
level_22	0DC7BCD28F129C086C25C81D4C0EBB3EDBA24216C4E87DA4917D41B152E1FF12	1/90	1.11%
level_23	90D95D9487758F3D7C9554C5CC418FE850AEDEA71BACD8738E939D233B70A899	1/76	1.32%
level_24	A2ACF8129D66971C7BB66F61BEBE5EEA58BA2FAF1BF87B9DDFB926D21C0A901F	1/79	1.27%
level_25	298F6D432A7D93E179AF2CCB780503F00A7C15ABC39E501D0820EBE6CDDF4C44	1/63	1.59%
level_26	A84C0A7226B54B05B0559FE422011204EA9CB337016E98899B60467D7ECA5010	1/62	1.61%
level_27	79D3D75D05D0F3184ECF1098D3C760A0B0C888E3D9A3234B349210E635C8C1AE	1/43	2.33%
level_28	B426039423ABE1D30D370EDB1AB93DB8214F45842EB77F1290F2A0B343492C2E	1/59	1.69%
level_30	6423897A25C95C60E9584BD1D4A1898820A6D02E1AD28545C05AD9B1BA620CAD	1/63	1.59%
level_31	58C5FED3E371B85DF6269ED6F85BAA060D8CFE2EFFFDFBA115CC33CDE09189F0	1/70	1.43%
level_32	6D20E28BC7DDC45EEB48A11D2B94BD9B6DA23F37BFE58A159A32A1A68DEECC32	1/98	1.02%
level_33	1E80F108F3781C9DD2AE1180ECC6A364B0C785600BDA1ADB19AFB6B588B4E17C	1/83	1.20%
level_34	E7DEF9DD29BC3D51E4B57583C19D5C4D1123E241133D91410459312C990F1923	1/87	1.15%
level_35	FF1F35A60353B5276F5AFD2AA72A23C7B2B64822FC7EC5D336125B81D6522DD2	1/67	1.49%
level_36	81FF24700513C90261FFDA1C9028E0D80B517034CB09685579DB69AEBB90C04B	1/52	1.92%
level_37	22DBD9CBDAF3EE278FDFA5BB87701BBFFF31B9CC0345C7D0DDF5F25DA9931BE7	1/57	1.75%
level_38	84B47DF569AC584E530FCA8CB4D2952860F25FA53637CBD8776F9F2CAC3C06E9	1/59	1.69%
level_40	4DE201FC7E423B518160361C743143A8669D538783337C2D11218C2C2A2642A2	1/57	1.75%
level_41	99E04DDA32B461C65DE303BAC8E55D357CD0A6D87495CF430E748C1E469323AE	1/81	1.23%
level_42	DB4F017CD24C2A53E625C0A1C68AA645491C1A822CF5C31F424E2236E58F1A04	3/74	4.05%
level_43	30E19C0BF7EB843C38B3A21C18DC3ED4E79AB1887BC7A90AEA0EA905349767C9	4/79	5.06%
level_44	372FDF9B8551C4FC8BE6DADFC0B8F012D6358B8C2B0560B47A9858E19B0CFD95	1/74	1.35%
level_45	6B3C55B68394E9E3035198949C2025E46D2FB4A31109B51BB88C355C7D7F2E1F	1/64	1.56%
level_46	42B5819A5AE3BBA0E07A4282D5CD74AC819CBC5A486F8AAE06545AC77C287EA2	1/68	1.47%
level_47	C22DE0B15E994D996602752F826A2080DC489AD94D0F41DD27CA2DC9D472370F	1/54	1.85%
level_48	9EEEA655BDF20CF9F7942A34D24CC36C38B0852E18B9D16D51D663F6066B9427	1/60	1.67%
level_50	EF5315F73D48DA658434315E2261EB5C4523AD80277CE97F31D200D3DE94AD2F	1/98	1.02%
cutscene_61	A189DA2821DAC4911D3922E7E4B2BD1316463E7651C8FCE554DBA2510E7A53BE	11/27	40.74%
cutscene_62	F81C232BE9389461EBA93814CCA9F90347DDCF8B164AE7BDBD213E1CCEC67E3F	11/30	36.67%
cutscene_63	7EE9BB459BBDA5D1232346E1F5A5EB507EEDE774D2BB4284E2DF8298CF06A2DE	5/28	17.86%
cutscene_64	0F80616B66705A97C3604A52A91139140D9E78D69635EA5A8FFCEAE96F2431F4	5/29	17.24%
cutscene_65	F3058F57B292F4E744F16B6278172376608EA2DA700A373F0C11A4DBCBBFEBF5	5/26	19.23%
cutscene_66	49EB8AD4581ECF4CC11BCC10CD4E9F675CBB9C24CE836F76BF20EFBD9C2DB378	5/26	19.23%
cutscene_67	EDD3D01A604B182D8A610AE976F83C09F953B3B07B881C556A47E1BFC36AD176	5/28	17.86%
cutscene_68	A0DFADECA23F1B2A893566F3B3552063B84C2B7DAB1B2A95BB6F5E5E642C3C4F	5/26	19.23%
cutscene_69	6B8F4BD9DB15BE9CBCF55BE06032FEE0B75AE9B8517F394D108BCF07E4E79948	5/27	18.52%
cutscene_70	7037E261E4333EDE3C62F635CC60E689192B1EBB4F1302D0D061240D04F001F7	5/26	19.23%
cutscene_71	535FBA45489BB891623FA0C12557BF06015C76315FD3DB4D3072CA9C11D1E43A	5/26	19.23%
cutscene_73	CE20FD06035F8A3BEEC5D55D623A2242891FAECF6FAC8D0A7A7C646C9F3DAD53	5/31	16.13%
cutscene_74	3A9E83C3B0C18532A3B08B8E397A0ACC71385FE2B66EA0036BDA53400FF71E6E	5/26	19.23%
cutscene_75	F0619BDD02CCE373AE8D7534EF8AF6B465687022E9756383C80A75591A1EC96F	5/27	18.52%
cutscene_76	D88EA50BDFC1A894AE230972EEFE2D690E0B70D3AAC883302E1833962E0588F1	5/27	18.52%
cutscene_77	14929F914246D6F2201EEBAE148074495275BB7F565E0F426307A9166C500125	5/27	18.52%
cutscene_78	CA70FAF92EE688EC4D90BE9DE9C92950F365F57CBC6E194067EEB79521174BFE	5/29	17.24%
cutscene_79	3A8FBA1F080A3C2070BE80A7BF370C2BFBA8F759482868424140A8B9F62055E9	5/26	19.23%
cutscene_80	07B1A96059B8FA216A987E984CC513B734C76C8A5BBD2505B7A2AED2066BFE48	5/26	19.23%

Building

Executing docker_env.sh starts a container in interactive mode with the Dockerfile image, which comes with modern mipsel- gcc and binutils. For the source code, a much older compiler will be used, gcc2.7.2-mipsel.

After starting the container, executing python3 ./build.py will create the main executable, named PSX.EXE in the /build folder. The overlays will be output to /build/wad. Alternatively, you can fun python3 ./build_multiproc.py when building to speed up the build process by multiprocessing. A Makefile is also included, but I've not really tested this yet, and it doesn't support running the antipiracy correction.

By default, the build.py script does not produce overlays that have fixed antipiracy checksums or the appropriate encryption, and as such these are not usable for gameplay purposes. In order to build playable files, you'll need to turn on the FIX_CHECKSUMS flag in the script. This increases the length of the build process significantly so it's not recommended that you keep this setting on, but it's necessary when producing a build for testing. In addition, the first time you run this, you'll want to set COMPILE_DRAGONBREATH to "True" to compile a local copy of the Dragonbreath antipiracy tool.

Because this project primarily concerns the game's code, you will need a copy of the game for its assets. A separate tool such as wadtool is needed to rebuild the WAD.WAD file. Edits to any non-overlay WADs (such as level data) will also require a separate tool. For creating the CD image, I would recommend mkpsxiso.

I have also included a pair of shell scripts prepare_cd.sh and build_cd.sh which use the aforementioned wadtool and mkpsxiso to extract the contents of a disc image, produce a build config file, extract the WAD.WAD file, copy the built overlay files across, rebuild the WAD, and recreate the disc image. The user may need to edit the build configuration file manually to ensure that the SPEECH.STR file is always at an offset of 90000, if they are using this decompilation to mod the game.

Additional Tools

• python3 progress.py will generate values to put into the README progress tables.
  • Manual updates to the progress files in /progress is required first.
• python3 context.py will generate a context file appropriate for use in decomp.me.

File Structure

The following assumptions have been made in determining an appropriate file structure for the project:

• The EXE appears to be split into a series of files that are roughly in alphabetical order. Most of these file names are guesses based on known official terminology, though some filenames have been observed in debug strings in Spyro the Dragon and Ratchet and Clank.
  • Splitting is also based on how the rodata is ordered. Strings and data appear at the top of a file, switch statements appear lower down.
• Overlays also appear to be built from multiple files. A rough file splitting was determined from the rodata for each overlay.
  • Level overlays appear to be particularly difficult, as rodata suggests that there is probably one file per moby, and this is also corroborated by debug strings in Ratchet and Clank which suggest the same would be true for that game. For now, all mobys have been put into a single file per level, but these may be split up later on if we can figure out how to reuse object files across different overlays. This might make adding new moby classes a bit of a pain though as it'd also probably mean updating the ld manually, so some part of the process probably needs to be automated.
  • The "level.c" files probably split up, too. There is some proof of what these splits are and how they affect the rodata for a given level; weirdly, the strings appear to go at the bottom of the level files instead of the top.
  • Many functions (e.g. saving and loading functions, moby functions, etc.) are shared by multiple levels. Currently it's not clear exactly how this was achieved, but where possible we will avoid repeat implementations of the same function.

Currently Unsupported Features

• In the long term, mobys should probably each have their own C file in /src/moby, so that each moby only needs to be built once. It's not clear how this will work, if it'll work at all.
  • There is evidence in the rodata structure for the overlays that each moby had a separate source file, rather than all of them sitting in one moby file per overlay.
  • Most mobys are the same across all levels. Mobys that aren't will need to be handled somewhat differently - eggs are one example.
  • Overlays contain a lot of common functions even outside of the moby code. Ideally, much of these will be implemented using #includes similar to how moby_spawn.inc.h currently works.
• All PsyQ / library functions and variables are implemented by included assembly files. The PsyQ compiler and linker are not used and thus specific features it implements may be done slightly differently in this repository.

Contribution Policy

Contributions are greatly appreciated, and this is not a project that I will be able to do all by myself. How you choose to contribute is left up to the contributor, but I ask a few things for you to consider before submitting a pull request:

• Where possible, try to align with the naming schemes and code style with other functions already in the repo. Even better if you can align them with the spyro-1 project, as longer-term these two repositories will be as aligned as possible.
• Please do not co-author commits using an AI agent. Agent context files will not be accepted into the main repository.
• Please ensure that the executable and all overlays are matching before submitting a pull request.

All PRs will be subject to scrutiny before being accepted, and it may take some time before I am able to review them. Please bear with me when a request is made!

Other Resources

• The MobyDoc contains a list of all of the moby classes in this game.

Acknowledgements

• splat and its various example projects
• spimdisasm disassembler used by splat
• maspsx
• decomp.me, a very handy tool for matching functions
• Altro50 and his Spyro 1 decomp

---

First try rat? Smiley face