drawing sine wave in canvas
Use bezierCurveTo
, this is only an example you should adjust parameters to get nice sinusoid
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.moveTo(50,50);
ctx.bezierCurveTo(120,-100,200,250,250,50);
ctx.bezierCurveTo(300,-100,350,250,430,50);
ctx.lineWidth = 5;
ctx.strokeStyle = '#003300';
ctx.stroke();
<canvas id="myCanvas" width="550" height="360" style="border:1px solid #d3d3d3;">
Old question but of very universal interest.
All answers here are very usefull but none has well commented code, so I've created a snippet that explains what is happening at every point and draws many variables for clarity. Thanks everyone for helping me understand, I hope this helps some one else.
var c = document.getElementById("canvas"); // Grab canvas object
var ctx = c.getContext("2d"); // Define canvas context
var w=c.width; // Canvas width => Frequency is relative to this
var h=c.height/2; // Canvas height over two => Amplitude: Volume
var f=1; // How many cycles per canvas width => Frequency: Tone & Speed
// Calculates y position from x
function calcSineY(x) {
// This is the meat (unles you are vegan)
// Note that:
// h is the amplitude of the wave
// x is the current x value we get every time interval
// 2 * PI is the length of one cycle (full circumference)
// f/w is the frequency fraction
return h - h * Math.sin( x * 2 * Math.PI * (f/w) );
}
function drawSine(x){
ctx.clearRect(0, 0, w, h*2);
//draw x axis
ctx.beginPath(); // Draw a new path
ctx.strokeStyle = "green"; // Pick a color
ctx.moveTo(0,h); // Where to start drawing
ctx.lineTo(w,h); // Where to draw to
ctx.stroke(); // Draw
// draw horizontal line of current amplitude
ctx.beginPath(); // Draw a new path
ctx.moveTo(0,h); // Where to start drawing
ctx.strokeStyle = "gray"; // Pick a color
for(var i=0;i<x;i++){ // Loop from left side to current x
var y = calcSineY(x); // Calculate y value from x
ctx.moveTo(i,y); // Where to start drawing
ctx.lineTo(x,y); // Where to draw to
}
ctx.stroke(); // Draw
// draw amplitude bar at current point
ctx.beginPath(); // Draw a new path
ctx.strokeStyle = "red"; // Pick a color
for(var i=0;i<x;i++){ // Loop from left side to current x
var y = calcSineY(x); // Calculate y value from x
ctx.moveTo(x,h); // Where to start drawing
ctx.lineTo(x,y); // Where to draw to
}
ctx.stroke(); // Draw
// draw area below y
ctx.beginPath(); // Draw a new path
ctx.strokeStyle = "orange"; // Pick a color
for(var i=0;i<x;i++){ // Loop from left side to current x
if(i/3==Math.round(i/3)) { // Draw only one line each 3 pixels
var y = calcSineY(i); // Calculate y value from x
ctx.moveTo(i,h); // Where to start drawing
ctx.lineTo(i,y); // Where to draw to
}
}
ctx.stroke(); // Draw
// draw sin curve point to point until x
ctx.beginPath(); // Draw a new path
ctx.strokeStyle = "black"; // Pick a color
for(var i=0;i<x;i++){ // Loop from left side to current x
var y = calcSineY(i); // Calculate y value from x
ctx.lineTo(i,y); // Where to draw to
}
ctx.stroke(); // Draw
}
// Define initial value of x positiom (leftmost side of cnanvas)
var x=0;
// Start time interval
var interval = setInterval(function(){
drawSine(x); // Call draww function every cycle
x++; // Increment x by 1
if(x>w){
x=0; // x cannot be more than canvas with, so back to 0
f++; // increment frequency for demonstration
}
},10); // Loop every 10 milliseconds
<canvas id="canvas" width="320" height="120" style="border:1px solid #999;">
Your code is unnecessarily difficult. Try it so simple:
var c = document.getElementById("myCanvas"); // get the canvas object to draw onto
var ctx = c.getContext("2d"); // will use simpe 2D context on the canvas
for(x=0; x<360; x += 20) { // 360 steps for entire sine period
ctx.moveTo(x+10,180); // for dashed line, go to start of next dash
ctx.lineTo(x,180); // then draw the short line
}
ctx.moveTo(0,180); // back to the left before drawing the sine
for(x=0; x<=360; x+=1) { // 360 steps (degrees) for entire sine period
y = 180.0 - Math.sin(x*Math.PI/180)*120; // calculate y flipped horizontally, converting from DEG to RADIAN
ctx.lineTo(x,y); // draw the point
}
ctx.stroke(); // strokes the drawing to the canvas
<canvas id="myCanvas" width="360" height="360" style="border:1px solid #d3d3d3;">
You are increasing counter
with a value that it too high, make it smaller:
var increase = 90/180*Math.PI / 9;
Draw the whole width of the diagram instead of half:
for(i=0; i<=360; i+=10){
You need a higher amplitude:
y = 180 - Math.sin(counter) * 120;
Demo: http://jsfiddle.net/Guffa/gmhg61s6/5/