Pulp Mill (Pulp-To-Lua Transpiler)

Converts Pulp projects to the Lua SDK for the Panic Playdate.

This transpiler is primarily intended to improve performance of Pulp projects, but you can also use it to extend the project with Lua API functionality not available in Pulp.

Requirements

You must have python 3 installed, and the PIL or Pillow module as well. python3 -m pip install Pillow on the command line ought to suffice.

Usage

From your command line:

python3 pulplua.py MyPulpProject.json out/

You can then compile using pdc as normal:

    pdc out MyPulpProject.pdx
    PlaydateSimulator ./MyPulpProject.pdx

Inconsistencies

• The transpilation is likely not perfect. Some behaviour may differ. You are responsible for ensuring that your game performs as intended -- please test it after converting it to Lua! You can help improve pulp-to-lua by reporting behaviourial differences.
• Audio in particular may sound warped. There are a number of reasons for this. In general, you can avoid must or all of the warping by ensuring that notes are held longer than the sum of their instrument's attack and delay fields. If that's not feasible, you can try changing __FIREFOX_SOUND_COMPAT to false in main.lua after exporting, or modifying the SOUNDSCALE table in pulp.lua. This is an ongoing field of research, and you're welcome to contribute!
• Some Pulp files, especially ones which have been worked on extensively, contain seemingly-broken entries in their JSON, like booleans in place of an object. These may cause errors, and can probably be resolved by inserting a dummy object in its place, e.g. by copying the previous entry. If you can identify the cause of this problem, please report!
• The wrapping of words in dialogue windows is likely to be subtly different. You are invited to implement a better paginate() function (see pulp.lua)

Optimization Advice

While pulp-to-lua should already significantly improve performance by an order of magnitude at least, there are additional steps you can take to make sure your code runs optimally:

• Avoid using emit wherever possible. This function is slow and it is usually preferable to use call. Even if you want everything to handle the call, it's still faster to use tell and call manually.
• There is generally no need to replace string literals for tile IDs e.g. draw "white-tile" for draw 0. The transpiler will do this automatically if it can detect this.
• To improve performance, up to around ~150 variables will be declared as local by the transpiler, and it will select the variables that appear most frequently in the code. This is not necessarily the variables which are most frequently used at runtime! Do with this information what you will -- you may wish to reuse variable names where possible.
• mimic events can be heavily optimized by the transpiler for events that contain only one line and that line is mimic with a static name or id literal.

Extensions

The following capabilities are introduced by pulp-to-lua which are not in pulp originally:

Inline Lua

Any comments starting with // [LUA] will have this prefix stripped, allowing you to write raw Lua code. For example, to ensure that the data store saves when the game is closed (instead of saving only when rooms exit):

on loop do
    // [LUA] if playdate.gameWillTerminate() pulp:savestore() end
end

PDXINFO

Any comment of the form // [PDXINFO] key=value will replace the associated line in the pdxinfo file. For example:

// [PDXINFO] version=1.5.3

Warning: some bundle IDs can cause pdc to crash. It is advised not to customize pdxinfo until you have already fully built the game at least once.

Smooth Movement

Enable this within pulpscript by setting __PTLE_SMOOTH_MOVEMENT_SPEED = 0.25 (or to any value between 0 and 1). This causes the player's position to smoothly interpolate while moving. You can set it back to 0 at any point in order to restore normal movement, even temporarily. While the player is in motion, it will be as though config.listen is false, so no additional inputs can be had until the player reaches the destination.

When drawing, you can add the values __PTLE_SMOOTH_OFFSET_X and __PTLE_SMOOTH_OFFSET_Y to a coordinate to make it appear at the player's location.

Of course, when using regular (non-milled) pulp, these values will all default to 0, so no unexpected behaviour will occur by adding __PTLE_SMOOTH_OFFSET_X or __PTLE_SMOOTH_OFFSET_Y. Therefore, there is no need to check for the occurrence of transpilation from within the code.

DAS Detection

When config.inputRepeat = 1, held inputs get repeated ("Delayed Auto-Shift"). In the update, confirm, and cancel events, __PTLE_CONFIRM_DAS, __PTLE_CANCEL_DAS, __PTLE_V_DAS (vertical d-pad), and __PTLE_H_DAS (horizontal d-pad) are set to 1 when the input is repeated, and -1 otherwise.

Legacy Sound

To use the sound engine for sfx from before the 1.10.0 update, place the following comment in any pulp code block. (Note that this does not affect music.)

// [PTL] legacySound=True

Debug FPS

To display the frame rate during runtime, place the following comment in any pulp code block:

// [PTL] showFPS=True

Contributions

Contributions are welcome! Ask the author (NaOH#1432 on discord) for advice.