vail/static/chart.mjs

124 lines
3.2 KiB
JavaScript

/** @typedef {Number} Duration */
const Millisecond = 1
const Second = 1000 * Millisecond
/**
* A chart of historical values.
*
* Curently this assumes all values are between 0 and 1,
* since that's all I need.
*/
class HistoryChart {
/**
* @param {Element} canvas Canvas element to draw on
* @param {string} style style to draw in; falls back to the `data-style` attribute
* @param {Duration} duration Time to display history for
*/
constructor(canvas, style=null, duration=20*Second) {
this.canvas = canvas
this.ctx = canvas.getContext("2d")
this.duration = duration
this.data = []
// One canvas pixel = 20ms
canvas.width = duration / (20 * Millisecond)
// Set origin to lower-left corner
this.ctx.scale(1, -1)
this.ctx.translate(0, -canvas.height)
this.ctx.fillStyle = style || canvas.dataset.color || "black"
this.ctx.lineWdith = 2
this.running=true
this.draw()
}
/**
* Set value to something at the current time.
*
* This also cleans up the event list,
* purging anything that is too old to be displayed.
*
* @param {Number} value Value for the event
*/
Set(value) {
this.SetAt(value)
}
/**
* Set value to something at the provided time.
*
* This also cleans up the event list,
* purging anything that is too old to be displayed.
*
* @param {Number} value Value for the event
* @param {Number} when Time to set the value
*/
SetAt(value, when=null) {
let now = Date.now()
if (!when) when=now
this.data.push([when, value])
this.data.sort()
let earliest = now - this.duration
// Leave one old datapoint so we know the value when the window opens
while ((this.data.length > 1) && (this.data[1][0] < earliest)) {
this.data.shift()
}
}
Stop() {
this.running = false
}
draw() {
let now = Date.now()
let earliest = now - this.duration
let xScale = this.canvas.width / this.duration
let yScale = this.canvas.height
let y = 0
let x = 0
this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height)
for (let point of this.data) {
let x2 = (point[0] - earliest) * xScale
let y2 = point[1] * yScale
if (y > 0) {
this.ctx.fillRect(x, 0, x2-x, y)
}
x=x2
y=y2
}
if (y > 0) {
this.ctx.fillRect(x, 0, this.canvas.width, y)
}
if (this.running) {
requestAnimationFrame(() => this.draw())
}
}
}
/**
* Return a new chart based on an HTML selector
*
* @param selector HTML selector
* @param style fill style
* @param duration duration of chart window
* @returns new chart, or null if it couldn't find a canvas
*/
function FromSelector(selector, style, duration=20*Second) {
let canvas = document.querySelector(selector)
if (canvas) {
return new HistoryChart(canvas, style, duration)
}
return null
}
export {HistoryChart, FromSelector}