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/**
* Relabi waveform display
* @module src/relabi/canvas.js;
*/
export default class RelabiCanvas {
/**
* Initialize relabi wave renderer
*/
constructor({ relabi, parent }) {
this.relabi = relabi;
this.height = 400;
this.lastFrame = 0;
this.lastAppendTime = 0;
this.lastAppendFrame = 0;
// Speed of the wave in pixels per second
this.speed = 1 / 5;
// Attach to the DOM
this.parent = parent = document.body;
this.canvas = document.createElement("canvas");
this.ctx = this.canvas.getContext("2d");
this.parent.appendChild(this.canvas);
// Initialize array
this.values = new Array(window.innerWidth).fill(0);
this.append([]);
// Clear the canvas
this.resize();
// Start drawing
this.requestAnimationFrame(0);
}
/**
* Draw the next frame
*/
requestAnimationFrame(frame) {
requestAnimationFrame((frame) => {
this.requestAnimationFrame(frame);
});
this.paint(frame);
this.lastFrame = frame;
}
/**
* Handle window resize
*/
resize() {
this.canvas.width = window.innerWidth;
this.canvas.height = this.height;
}
/**
* Clear the canvas
*/
clear() {
this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
/**
* Append values
*/
append(time, values) {
this.lastAppendTime = time;
this.lastAppendFrame = this.lastFrame;
this.values = this.values.concat(values).slice(-this.canvas.width);
}
/**
* Paint the canvas
*/
paint(frame) {
this.clear();
this.drawRelabiWave(frame);
this.drawBounds();
}
/**
* Draw the bounds
*/
drawBounds() {
const { canvas, ctx } = this;
const { width, height } = canvas;
// Draw dashed lines for all bounds
for (const bound of this.relabi.bounds) {
const y = getWaveHeight(bound.level, height);
ctx.beginPath();
ctx.setLineDash([10, 5]);
ctx.strokeStyle = bound.color || "#888";
ctx.moveTo(0, y);
ctx.lineTo(width, y);
ctx.stroke();
}
}
/**
* Draw the relabi wave
*/
drawRelabiWave(frame) {
const { canvas, ctx } = this;
const { width, height } = canvas;
const pointCount = this.values.length;
let index = 0;
// Start the path
ctx.beginPath();
ctx.strokeStyle = "white";
ctx.setLineDash([]);
// This is the offset in seconds from the last frame we computed
const frameOffset = (frame - this.lastAppendFrame) / 1000;
// Make a path connecting all values
for (const point of this.values) {
if (!point) {
index += 1;
continue;
}
const [time, value] = point;
// This is the offset of this time from current time
// If this is in the future, it will be positive.
// Subtracting the frame offset pulls it negative.
const timeOffset = this.lastAppendTime + frameOffset - time;
const x = width - timeOffset * this.speed * width - 10;
if (x < 0) {
continue;
}
const y = getWaveHeight(value, height);
if (index === 0) {
ctx.moveTo(x, y);
}
ctx.lineTo(x, y);
index += 1;
}
// Paint the line
ctx.stroke();
}
}
/**
* Get the height of the wave at a given value
*/
const getWaveHeight = (value, height) => ((value + 1) / 2) * height;
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