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function GraphPlot(canvas) {
this.canvas = canvas
const g = canvas.getContext('2d')
if (g == null) {
throw new Error('failed to acquire 2d context')
}
this.width = 0 // dp
this.height = 0 // dp
this.widthPx = 0 // px
this.heightPx = 0 // px
this.pixelRatio = 1
this.g = g
this.dataSegments = []
this.axes = {
x0: .5, // % from left to x=0
y0: .5, // % from top to y=0
scalex: 40, // pixels from x=0 to x=1
scaley: 40, // pixels from y=0 to y=1
negativeX: true,
}
if (!this.autosize()) {
this.setSize(256, 256)
}
}
GraphPlot.prototype.autosize = function() {
try {
this.canvas.width = null
this.canvas.height = null
this.canvas.style.width = null
this.canvas.style.height = null
var cs = window.getComputedStyle(this.canvas)
var width = parseFloat(cs.width)
var height = parseFloat(cs.height)
this.setSize(width, height)
return true
} catch (err) {
if (typeof console != 'undefined' && console.warn) {
console.warn('GraphPlot.autosize failed: ' + err)
}
}
return false
}
// setOrigin sets the origin of axis x and y
// The values should be in the range [0-1] and maps to the extremes
// of the canvas.
//
GraphPlot.prototype.setOrigin = function(x, y) {
var p = this
p.axes.x0 = x
p.axes.y0 = y
}
// setScale sets the value scale for x and y axis.
// The values should be provided as display points.
//
GraphPlot.prototype.setScale = function(x, y) {
var p = this
if (y === undefined) {
y = x
}
p.axes.scalex = x
p.axes.scaley = y
}
// setSize sets the size of canvas in display points
//
GraphPlot.prototype.setSize = function(width, height) {
var p = this
p.width = width
p.height = height
const el = p.canvas, g = p.g
p.pixelRatio = window.devicePixelRatio || 1
if (p.pixelRatio != 1) {
el.width = p.widthPx = width * p.pixelRatio
el.height = p.heightPx = height * p.pixelRatio
g.scale(p.pixelRatio, p.pixelRatio)
} else {
el.width = p.widthPx = width
el.height = p.heightPx = height
g.scale(1, 1)
}
el.style.width = `${width}px`
el.style.height = `${height}px`
}
GraphPlot.prototype.renderAxes = function() {
var p = this
, g = p.g
, x0 = Math.round(p.axes.x0 * p.widthPx) / p.pixelRatio
, y0 = Math.round(p.axes.y0 * p.heightPx) / p.pixelRatio
g.beginPath()
g.strokeStyle = "rgb(0, 0, 0, 0.2)"
if (y0 > 0 && y0 < p.width) {
g.moveTo(0, y0); g.lineTo(p.width, y0) // X axis
}
if (x0 > 0 && x0 < p.height) {
g.moveTo(x0, 0); g.lineTo(x0, p.height) // Y axis
}
g.stroke()
}
// plotf plots an arbitrary function on the graph
//
GraphPlot.prototype.plotf = function(f, color) {
var p = this
, g = p.g
, w = p.width
, h = p.height
, x0 = p.axes.x0 * p.width
, y0 = p.axes.y0 * p.height
, x = 0
, y = 0
, dx = 4 / p.pixelRatio // smaller means finer curves and more CPU
, scalex = p.axes.scalex * w
, scaley = p.axes.scaley * h
, iMax = Math.round((w - x0) / dx)
, iMin = p.axes.negativeX ? Math.round(-x0 / dx) : 0
g.beginPath()
g.lineWidth = 1
g.strokeStyle = color || "rgb(0, 0, 0, 0.8)"
for (var i = iMin; i <= iMax; i++) {
x = dx * i
y = f(x / scalex) * scaley
if (i == iMin) {
g.moveTo(x0 + x, y0 - y)
} else {
g.lineTo(x0 + x, y0 - y)
}
}
g.stroke()
}
// plotLines draws straight lines between a collection of points
//
GraphPlot.prototype.plotLine = function(points, color) {
var p = this
, g = p.g
, x0 = p.axes.x0 * p.width
, y0 = p.axes.y0 * p.height
, x = 0
, y = 0
, scalex = p.axes.scalex * p.width
, scaley = p.axes.scaley * p.height
, pt
g.beginPath()
g.lineWidth = 1
g.strokeStyle = color || "rgb(0, 0, 0, 0.8)"
var i = 0
for (; i < points.length; i++) {
pt = points[i]
x = pt[0] * scalex
y = pt[1] * scaley
if (i == 0) {
g.moveTo(x0 + x, y0 - y)
} else {
g.lineTo(x0 + x, y0 - y)
}
}
g.stroke()
}
// plotPoints draws points
//
GraphPlot.prototype.plotPoints = function(points, color) {
var p = this
, g = p.g
, x0 = p.axes.x0 * p.width
, y0 = p.axes.y0 * p.height
, x = 0
, y = 0
, scalex = p.axes.scalex * p.width
, scaley = p.axes.scaley * p.height
, pt
, i = 0
g.fillStyle = color || "rgb(0, 0, 0, 0.8)"
for (; i < points.length; i++) {
pt = points[i]
x = x0 + pt[0] * scalex
y = y0 - pt[1] * scaley
g.beginPath()
g.arc(x, y, 3, 0, Math.PI + (Math.PI * 2) / 2, false)
g.fill()
}
}
GraphPlot.prototype.clear = function() {
var p = this
p.g.clearRect(0, 0, p.width, p.height)
p.renderAxes()
}
GraphPlot.prototype.renderDemo = function() {
var p = this
, g = p.g
, dpscale = p.pixelRatio
, w = p.widthPx
, h = p.heightPx
p.clear()
p.plotf(
function(x) { return Math.sin(x) },
'blue'
)
p.plotf(
function(x) { return Math.cos(3*x) },
'hotpink'
)
// var scale = p.height / 4
// g.moveTo(0, scale)
// var i, sine, lines = 200, frag = p.width / lines
// for (i = 0; i < lines; i++) {
// sine = Math.sin(i / scale * 2) * scale
// g.lineTo(i * frag, -sine + scale)
// }
// g.stroke()
}
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