Question

我试图在画布上绘制一个简单的正弦波，但我没有把它弄好。这是我想要的输出，如图所示。

到目前为止我所获得的是http://jsfiddle.net/RaoBurugula/gmhg61s6/4/

HTML 的

 <canvas id="myCanvas" width="360" height="360" style="border:1px solid #d3d3d3;">

JS

 var c = document.getElementById("myCanvas");
 var ctx = c.getContext("2d");
 var i;
 for(i=0; i<360; i+= 20){
    ctx.moveTo(i+5,180);
    ctx.lineTo(i,180);

 }
 ctx.stroke();
 var counter = 0, x=0,y=180;

 //100 iterations
 var increase = 90/180*Math.PI ;
 for(i=0; i<=180; i+=10){

 ctx.moveTo(x,y);
 x = i;
y=  180 - Math.sin(counter);
counter += increase;

ctx.lineTo(x,y);
alert( " x : " + x + " y : " + y) ;
}
ctx.stroke();

我想要的输出

My desired output

Answer 1

您正在增加counter，其值太高，请将其缩小：

var increase = 90/180*Math.PI / 9;

绘制图表的整个宽度而不是一半：

for(i=0; i<=360; i+=10){

你需要更高的幅度：

y =  180 - Math.sin(counter) * 120;

演示：http://jsfiddle.net/Guffa/gmhg61s6/5/

Answer 2

您的代码非常困难。试试这么简单：

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");

for(x=0; x<360; x += 20){
    ctx.moveTo(x+5,180);
    ctx.lineTo(x,180);
}
ctx.moveTo(0,180);

for(x=0; x<=360; x+=1){
    y = 180.0 - Math.sin(x*Math.PI/180)*120;
    ctx.lineTo(x,y);
}
ctx.stroke();

Answer 3

<pre>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var i;
var amplitude=90;
var width=c.width;
var xAxis=300;
var step=1;
var frequency=4;
ctx.moveTo(0,250);
ctx.lineTo(width,250);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(0,250);
var c=width/Math.PI/(frequency*2);
for(i=0; i<width; i+=step){
   var x = amplitude * Math.sin(i /c);
  ctx.lineTo(i,250+x);


}
ctx.strokeStyle = '#0096FF';

ctx.stroke();
</pre>

Answer 4

使用bezierCurveTo，这只是一个示例，您应该调整参数以获得良好的正弦曲线

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;">

Answer 5

古老的问题却引起了广泛关注。

这里的所有答案都非常有用，但没有一个注释得很好的代码，因此，我创建了一个片段，解释了每个地方发生的情况，并为清晰起见绘制了许多变量。感谢大家帮助我理解，希望对您有所帮助。

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;">

Answer 6

使用单循环，您可以轻松

＆＃13;

var c = document.getElementById("myCanvas");
      var ctx = c.getContext("2d");
    	var y=180;
      //draw axis
      ctx.beginPath();
      ctx.strokeStyle = "red";
      ctx.moveTo(0,  y/2);
      ctx.lineTo(y,  y/2);
      ctx.stroke();
      // draw sin wave
      ctx.beginPath();
      ctx.moveTo(x,y);
      ctx.strokeStyle = "black";
      for(var x=0; x<=180; x+=1){
          ctx.lineTo(x,((y/2)  + y/2  * Math.sin( ((x+-y/2)/90) * Math.PI)));
          ctx.stroke();
          }

＆＃13;

<canvas id="myCanvas" width="360" height="360" style="border:1px solid #d3d3d3;">

＆＃13;

https://i.stack.imgur.com/9oEN0.png

Answer 7

根据男服务生的回答：

<string name="name">Name %s</string>

String nameText =  getString(R.string.name,"khemraj");

#include <stdio.h>

int main() {
float x=0,y=0;
char dir;
float mile;

while(1){

    printf("Enter input direction as N,S,E,W (0 to exit): ");
    scanf("%c",&dir); 

    if(dir == '0')
        break;
    if(dir != 'N' && dir != 'S' && dir != 'E' && dir != 'W'){

        printf("Invalid Direction, re-enter \n");
        continue;
    }

    printf("Input mile in %c dir: ",dir);
    scanf("%f",&mile);
    if(dir == 'N'){
        y+=mile;
    }
    else if(dir == 'S'){
        y-=mile;
    }
    else if(dir == 'E'){
        x+=mile;
    }
    else if(dir == 'W'){
        x-=mile;
    }
}
 printf("\nCurrent position of A: (%4.2f,%4.2f)\n",x,y);
return 0;
}

Answer 8

function plotSine(amplitude, frequency) {
  const canvas = document.getElementById('canvas');
  if (canvas.getContext) {
    const ctx = canvas.getContext('2d');
    
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    
    ctx.beginPath();
    
    ctx.strokeStyle = '#343a40';
    ctx.lineWidth = 2;
    
    var x = 0;
    var y = 0;
    
    while (x < canvas.width) {
      y = (canvas.height / 2) + amplitude * Math.sin(x / frequency);
      ctx.lineTo(x, y);
      
      x += 1;
    }
    
    ctx.stroke();
  }
}

plotSine(40, 20);

code {
  background-color: #eee;
  border-radius: 3px;
  padding: 0 3px;
}

<canvas id="canvas" width="480" height="360">
  <p>
    Your browser does not support the <code>&lt;canvas&gt;</code> element.
  </p>
</canvas>

在画布上画正弦波

8 个答案: