Scroll HD Controller

a small nodejs module to communicate with a Pimonroni Scroll HD Pi Hat, ported from pimoroni's library

requires i2c-bus [git] and has ONLY been tested on a Raspberry Pi Zero W with node v9.10.1. >v8 will probably work, but I again haven't tested.

only provides the ability to display pixel arrays, and has no higher level functionality.

DOES NOT SUPPORT ANYTHING OTHER THAN THE SCROLL HD. sorry for shouting.

Installation

this will only work on a linux system with an i2c bus. on raspbian i2c is not enabled by default, here's some information on enabling it.

$ npm install git+https://git@github.com/whatsim/scrollcontroller.git

API

scrollController exports a class with three methods:

init()

// will return a promise which will be resolved when the display will be initialized
// you must call this method before any call to other methods

display(pixelArray, gammaAdjust = true)

// takes a pixel array, that is: a 119 length int array bounded between
// [0-255] where 255 is white and 0 is black. if you omit or pass `gammaAdjust` 
// as true, the display function will process the input array to conform to 
// the gamma curve from pimoroni. if you set it to false, the values are
// displayed as is. the pixel array starts in the upper left, goes across left
// to right, and then row by row.
// this method also return a promise which will be resolved when the display has been updated

clear()

// clear takes no arguments and blanks the display.
// this method return a similar promise than the display method

Usage

Here's a minimal example that shows an alternating field of pixels.

// get a reference to scrollcontroller
const scrollController = new(require('scroll-controller'))()

// make an array of 0-255 pixels
let arr = []

for(var i = 0; i < 119; i++){
    arr[i] = i%2 == 0 ? 255 : 0
}

scrollController.init().then(() => {
    scrollController.display(arr)
})

I've primarily used this library with node-canvas, like so:

// get a reference to scrollcontroller
const scrollController = new(require('scroll-controller'))()

// setup a canvas
const canvas = new Canvas(17,7)
const context = canvas.getContext('2d')

// draw something
context.fillStyle = 'rgba(255,255,255,1)'
context.fillRect(0,0,5,5)

// get a reference to the buffer backing the canvas and cast it to Unsigned Int
let imageBuffer = new Uint8Array(canvas.toBuffer('raw'))
let displayArray = []

// copy pixels out of the buffer into an array suitable to sending to 
// scrollController, note that the buffer from node canvas is ARGB, so
// we only copy one value for each 4 bytes in the buffer.

for(let i = 1; i < imageBuffer.length; i += 4){
	displayArray.push(imageBuffer[i])
}

// init and display
scrollController.init().then(() => {
    scrollController.display(displayArray)
})

Support

Hey so, this works for me. If you fix a bug and would like to share it back, please do a PR, but I may not be timely in replying. This is the 'put it on the internet in case it solves someones problem as is' sort of open source not 'be responsible for the continued function of other peoples projects for forever' sort of open source.

License

MIT 2018 http://whatsim.mit-license.org