var ctx = canvas.getContext("2d");
window.focus();
//==============================================================================
// the current data read speed
var dataSpeed = 1;
var samplesPerFrame = 1;
requestAnimationFrame(mainLoop); // start animation when code has been parsed and executed
//------------------------------------------------------------------------------
// data reader reads from a data source
const dataReader = {
readPos : 0,
seek(amount){ // moves read pos forward or back
if(this.data.length === 0){
this.readPos = 0;
return 0;
}
this.readPos += amount;
this.readPos = this.readPos < 0 ? 0 :this.readPos >= this.data.length ? this.data.length - 1 : this.readPos;
return this.readPos;
},
// this function reads the data at read pos. It is a linear interpolation of the
// data and does nor repressent what the actual data may be at fractional read positions
read(){
var fraction = this.readPos % 1;
var whole = Math.floor(this.readPos);
var v1 = this.data[Math.min(this.data.length-1,whole)];
var v2 = this.data[Math.min(this.data.length-1,whole + 1)];
return (v2 - v1) * fraction + v1;
},
}
//------------------------------------------------------------------------------
// Create a data source and add a dataReader to it
const dataSource = Object.assign({
data : [],
},dataReader
);
// fill the data source with random data
for(let i = 0; i < 100000; i++){
// because random data looks the same if sampled every 1000 or 1 unit I have added
// two waves to the data that will show up when sampling at high rates
var wave = Math.sin(i/10000) * 0.5;
wave += Math.sin(i/1000) * 0.5;
// high frequency data shift
var smallWave = Math.sin(i/100) * (canvas.height/5);
// get a gaussian distributed random value
dataSource.data[i] = Math.floor(smallWave + ((wave + Math.random()+Math.random()+Math.random()+Math.random()+Math.random())/5) * canvas.height);
}
//------------------------------------------------------------------------------
// Data displayer used to display a data source
const dataDisplay = {
writePos : 0,
width : 0,
color : "black",
lineWidth : 1,
// this function sets the display width which limits the data buffer
// when it is called all buffers are reset
setDisplayWidth(width){
this.data.length = 0;
this.width = width;
this.writePos = 0;
if(this.lastRead === undefined){
this.lastRead = {};
}
this.lastRead.mean = 0;
this.lastRead.max = 0;
this.lastRead.min = 0;
},
// this draws the buffered data scrolling from left to right
draw(){
var data = this.data; // to save my self from writing this a zillion times
const ch = canvas.height/2;
if(data.length > 0){ // only if there is something to draw
ctx.beginPath();
ctx.lineWidth = this.lineWidth;
ctx.strokeStyle = this.color;
ctx.lineJoin = "round";
if(data.length < this.width){ // when buffer is first filling draw from start
ctx.moveTo(0, data[0])
for(var i = 1; i < data.length; i++){
ctx.lineTo(i, data[i])
}
}else{ // buffer is full and write position is chasing the tail end
ctx.moveTo(0, data[this.writePos])
for(var i = 1; i < data.length; i++){
ctx.lineTo(i, data[(this.writePos + i) % data.length]);
}
}
ctx.stroke();
}
},
// this reads data from a data source (that has dataReader functionality)
// Speed is in data units,
// samples is number of samples per buffer write.
// samples is only usefull if speed > 1 and lets you see the
// mean, min, and max of the data over the speed unit
// If speed < 1 and sample > 1 the data is just a linear interpolation
// so the lastRead statistics are meaningless (sort of)
readFrom(dataSource,speed,samples){ // samples must be a whole positive number
samples = Math.floor(samples);
var value = 0;
var dataRead;
var min;
var max;
for(var i = 0; i < samples; i ++){ // read samples
dataSource.seek(speed/samples); // seek to next sample
dataRead = dataSource.read(); // read the sample
if(i === 0){
min = dataRead;
max = dataRead;
}else{
min = Math.min(dataRead,min);
max = Math.min(dataRead,max);
}
value += dataRead;
}
// write the samples data and statistics.
this.lastRead.min = min;
this.lastRead.max = max;
this.lastRead.delta = value/samples - this.lastRead.mean;
this.lastRead.mean = value/samples;
this.data[this.writePos] = value/samples;
this.writePos += 1;
this.writePos %= this.width;
}
}
// display data buffer
var displayBuffer = Object.assign({ // this data is displayed at 1 pixel per frame
data : [], // but data is written into it at a variable speed
},
dataDisplay // add display functionality
);
//------------------------------------------------------------------------------
// for control
const keys = {
ArrowLeft : false,
ArrowRight : false,
ArrowUp : false,
ArrowDown : false,
}
function keyEvent(event){
if(keys[event.code] !== undefined){
event.preventDefault();
keys[event.code] = true;
}
}
addEventListener("keydown",keyEvent);
//------------------------------------------------------------------------------
function mainLoop(time){
ctx.clearRect(0,0,canvas.width,canvas.height);
if(canvas.width !== displayBuffer.width){
displayBuffer.setDisplayWidth(canvas.width);
}
displayBuffer.readFrom(dataSource,dataSpeed,samplesPerFrame);
displayBuffer.draw();
//-----------------------------------------------------------------------------
// rest is display UI and stuff like that
ctx.font = "16px verdana";
ctx.fillStyle = "black";
//var dataValue =displayBuffer.lastRead.mean.toFixed(2);
//var delta = displayBuffer.lastRead.delta.toFixed(4);
var readPos = dataSource.readPos.toFixed(4);
//if(displayBuffer.lastRead.delta > 0){ delta = "+" + delta }
// ctx.fillText("Data : " + dataValue + " (" +delta +")" ,4,18);
ctx.setTransform(0.9,0,0,0.89,4,18);
ctx.fillText("Speed : " + dataSpeed.toFixed(3) + ", Sample rate :" +samplesPerFrame + ", Read @ "+readPos ,0,0);
ctx.setTransform(0.7,0,0,0.7,4,32);
if(samplesPerFrame === 1){
ctx.fillText("Keyboard speed -left, +right Sample rate +up",0,0);
}else{
ctx.fillText("Keyboard speed -left, +right Sample rate -down, +up",0,0);
}
ctx.setTransform(1,0,0,1,0,0);
if(keys.ArrowLeft){
keys.ArrowLeft = false;
if(dataSpeed > 1){
dataSpeed -= 1;
}else{
dataSpeed *= 1/1.2;
}
}
if(keys.ArrowRight){
keys.ArrowRight = false;
if(dataSpeed >= 1){
dataSpeed += 1;
}else{
dataSpeed *= 1.2;
if(dataSpeed > 1){ dataSpeed = 1 }
}
}
if(keys.ArrowUp){
keys.ArrowUp = false;
samplesPerFrame += 1;
}
if(keys.ArrowDown){
keys.ArrowDown = false;
samplesPerFrame -= 1;
samplesPerFrame = samplesPerFrame < 1 ? 1 : samplesPerFrame;
}
requestAnimationFrame(mainLoop);
}
canvas {
border : 2px black solid;
}
<canvas id=canvas width=512 height=200></canvas>
requestAnimationFrameコールバックは、最初の引数としてタイムスタンプを受け取ります。これを使用して、現在のコールと最後のコールの差を計算することができます。次に、2つのアニメーションフレームの間に渡された時間に基づいて計算を実行します。 –
それは、フィドルの波をスピードアップすることは可能ですか？ –
はい、アニメーションフレーム内で現在何をやり直しているかは、2つのフレームの間の時間に比例します。 –