Creating your first app

Your First App

Creating an app is incredibly straightforward. You only need two files in a directory inside /apps/ on the SD Card:

1. app.json: A simple file describing your app.

1     {
2         "name": "My Awesome App",
3         "description": "The best app ever.",
4         "version": "1.0"
5     }

2. main.lua: The entry point for your code, which runs in a simple loop.

 1     -- The 'picocalc' global is your gateway to the hardware
 2     local pc = picocalc
 3
 4     -- Main app loop
 5     while true do
 6         -- Check for the ESC key to exit back to the launcher
 7         if pc.input.getButtonsPressed() & pc.input.BTN_ESC ~= 0 then
 8             return
 9         end
10
11         -- Drawing
12         pc.display.clear(pc.display.BLACK)
13         pc.display.drawText(100, 150, "Hello, World!", pc.display.WHITE)
14         pc.display.flush() -- Push your changes to the screen
15
-- Sleep to maintain a steady frame rate (~60 FPS)
pc.sys.sleep(16)
end

Add an icon (optional)

Put an icon.png (or icon.bmp) next to app.json. The launcher draws it at 24×24 pixels beside the app’s name. Other sizes are scaled to fit with nearest-neighbour sampling, so draw at 24×24, or at an exact multiple such as 48×48, to keep the pixels crisp. Icons are drawn opaque: transparent PNG pixels come out black, so fill the whole square. The built-in icons use a dark navy background (RGB 12, 16, 48) behind their artwork. Without an icon, the launcher draws a game cartridge in the app’s category colour, with the first letter of the app’s name on its label.

Prefer C or C++?

If you want to build high-performance apps or prefer working in C/C++, check out our guide on Native App Development.