VVVVVV/desktop_version
Misa 3ca7b09012 Fix regression: quick stopping changing drawframe
This fixes a regression that desyncs my Nova TAS after re-removing the
1-frame input delay.

Quick stopping is simply holding left/right but for less than 5 frames.
Viridian doesn't decelerate when you let go and they immediately stop in
place. (The code calls this tapping, but "quick stopping" is a better
name because you can immediately counter-strafe to stop yourself from
decelrating in the first place, and that works because of this same
code.)

So, the sequence of events in 2.2 and previous looks like this:

- gameinput()
  - If quick stopping, set vx to 0
- gamerender()
  - Change drawframe depending on vx
- gamelogic()
  - Use drawframe for collision (whyyyyyyyyyyyyyyyyyyyyyyyyyyy)

And now (ignoring the intermediate period where the whole loop order was
wrong), the sequence of events in 2.3 looks like this:

- gamerenderfixed()
  - Change drawframe depending on vx
- gamerender()
- gameinput()
  - If quick stopping, set vx to 0
- gamelogic()
  - Use drawframe for collision (my mind has become numb to pain)

So, this means that all the player movement stuff is completely the
same. Except their drawframe is going to be different.

Unfortunately, I had overlooked that gameinput() sets vx and that
animateentities() (in gamerenderfixed()) checks vx. Although, to be
fair, it's a pretty dumb decision to make collision detection be based
on the actual sprites' pixels themselves, instead of a hitbox, in the
first place, so you'd expect THAT to be the end of the dumb parade. Or
maybe you shouldn't, I don't know.

So, what's the solution?

What I've done here is added duplicates of framedelay, drawframe, and
walkingframe, for collision use only. They get updated in gamelogic(),
after gameinput(), which is after when vx could be set to 0.

I've kept the original framedelay, drawframe, and walkingframe around,
to keep the same visuals as closely as possible.

However, due to the removal of the input delay, whenever you quick stop,
your sprite will be wrong for just 1 frame - because when you let go of
the direction key, the game will set your vx to 0 and the logical
drawframe will update to reflect that, but the previous frame cannot
know in advance that you'll release the key on the next frame, and so
the visual drawframe will assume that you keep holding the key.

Whereas in 2.2 and below, when you release a direction key, the player's
position will only update to reflect that on the next frame, but the
current frame can immediately recognize that and update the drawframe
now, instead of retconning it later.

Basically the visual drawframe assumes that you keep holding the key,
and if you don't, then it takes on the value of the collision drawframe
anyway, so it's okay. And it's only visual, anyway - the collision
drawframe of the next frame (when you release the key) will be the same
as the drawframe of the frame you release the key in 2.2 and below.

But I really don't care to try and fix this for if you re-enable the
input delay because it's minor and it'd be more complicated.
2021-07-28 20:11:16 -04:00
..
src Fix regression: quick stopping changing drawframe 2021-07-28 20:11:16 -04:00
.dockerignore Run CI on CentOS 7 (#574) 2021-01-11 00:30:15 -05:00
.gitignore Don't recompile all files when the commit hash is changed 2020-12-25 20:17:01 -05:00
CMakeLists.txt Quote CMAKE_CXX_FLAGS 2021-04-20 14:22:53 -04:00
CONTRIBUTORS.txt Support for OpenBSD 2021-06-13 10:48:20 -04:00
Dockerfile Run CI on CentOS 7 (#574) 2021-01-11 00:30:15 -05:00
README.md Update project generation snippet 2021-07-25 14:36:51 -04:00
version.cmake Update commit hash every time it changes, not just when CMake is re-ran 2020-12-26 00:15:47 -05:00

README.md

How to Build

VVVVVV's official desktop versions are built with the following environments:

  • Windows: Visual Studio 2010
  • macOS: Xcode CLT, currently targeting 10.9 SDK
  • GNU/Linux: CentOS 7

The engine depends solely on SDL2 2.0.14+ and SDL2_mixer. All other dependencies are statically linked into the engine. The development libraries for Windows can be downloaded from their respective websites, Linux developers can find the dev libraries from their respective repositories, and macOS developers should compile and install from source (including libogg/libvorbis/libvorbisfile).

Steamworks support is included and the DLL is loaded dynamically, you do not need the SDK headers and there is no special Steam or non-Steam version. The current implementation has been tested with Steamworks SDK v1.46.

To generate the projects on Windows:

# Put your SDL2/SDL2_mixer folders somewhere nice!
mkdir flibitBuild
cd flibitBuild
cmake -G "Visual Studio 10 2010" .. -DSDL2_INCLUDE_DIRS="C:\SDL2-2.0.14\include;C:\SDL2_mixer-2.0.4\include" -DSDL2_LIBRARIES="C:\SDL2-2.0.14\lib\x86\SDL2;C:\SDL2-2.0.14\lib\x86\SDL2main;C:\SDL2_mixer-2.0.4\lib\x86\SDL2_mixer"

Note that on some systems, the SDL2_LIBRARIES list on Windows may need SDL2/SDL2main/SDL2_mixer to have .lib at the end of them. The reason for this inconsistency is unknown.

To generate everywhere else:

mkdir flibitBuild
cd flibitBuild
cmake ..

macOS may be fussy about the SDK version. How to fix this is up to the whims of however Apple wants to make CMAKE_OSX_SYSROOT annoying to configure and retain each time Xcode updates.

Including data.zip

You'll need the data.zip file from VVVVVV to actually run the game! It's available to download separately for free in the Make and Play edition of the game. Put this file next to your executable and the game should run.

This is intended for personal use only - our license doesn't allow you to actually distribute this data.zip file with your own forks without getting permission from us first. See LICENSE.md for more details. (If you've got a project in mind that requires distributing this file, get in touch!)

A Word About Compiler Quirks

(Note: This section only applies to version 2.2 of the source code, which is the initial commit of this repository. Since then, much hard work has been put in to fix many undefined behaviors. If you're compiling the latest version of the source code, ignore this section.)

This engine is super fussy about optimization levels and runtime checks. In particular, the Windows version absolutely positively must be compiled in Debug mode, with /RTC enabled. If you build in Release mode, or have /RTC disabled, the game behaves dramatically different in ways that were never fully documented (bizarre softlocks, out-of-bounds issues that don't show up in tools like Valgrind, stuff like that). There are lots of things about this old code that could be cleaned up, polished, rewritten, and so on, but this is the one that will probably bite you the hardest when setting up your own build, regardless of platform.

We hope you'll enjoy messing with the source anyway!

Love, flibit