Draw on HTML5 Canvas using a mouse-第2页回答

2楼-- · 2019-01-02 17:21

Here's the most straightforward way to create a drawing application with canvas:

Attach a mousedown, mousemove, and mouseup event listener to the canvas DOM
on mousedown, get the mouse coordinates, and use the moveTo() method to position your drawing cursor and the beginPath() method to begin a new drawing path.
on mousemove, continuously add a new point to the path with lineTo(), and color the last segment with stroke().
on mouseup, set a flag to disable the drawing.

From there, you can add all kinds of other features like giving the user the ability to choose a line thickness, color, brush strokes, and even layers.

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孤独总比滥情好

3楼-- · 2019-01-02 17:22

I was looking to use this method for signatures as well, i found a sample on http://codetheory.in/.

I've added the below code to a jsfiddle

Html:

<div id="sketch">
    <canvas id="paint"></canvas>
</div>

Javascript:

 (function() {
    var canvas = document.querySelector('#paint');
    var ctx = canvas.getContext('2d');

    var sketch = document.querySelector('#sketch');
    var sketch_style = getComputedStyle(sketch);
    canvas.width = parseInt(sketch_style.getPropertyValue('width'));
    canvas.height = parseInt(sketch_style.getPropertyValue('height'));

    var mouse = {x: 0, y: 0};
    var last_mouse = {x: 0, y: 0};

    /* Mouse Capturing Work */
    canvas.addEventListener('mousemove', function(e) {
        last_mouse.x = mouse.x;
        last_mouse.y = mouse.y;

        mouse.x = e.pageX - this.offsetLeft;
        mouse.y = e.pageY - this.offsetTop;
    }, false);


    /* Drawing on Paint App */
    ctx.lineWidth = 5;
    ctx.lineJoin = 'round';
    ctx.lineCap = 'round';
    ctx.strokeStyle = 'blue';

    canvas.addEventListener('mousedown', function(e) {
        canvas.addEventListener('mousemove', onPaint, false);
    }, false);

    canvas.addEventListener('mouseup', function() {
        canvas.removeEventListener('mousemove', onPaint, false);
    }, false);

    var onPaint = function() {
        ctx.beginPath();
        ctx.moveTo(last_mouse.x, last_mouse.y);
        ctx.lineTo(mouse.x, mouse.y);
        ctx.closePath();
        ctx.stroke();
    };

}());

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残风、尘缘若梦

4楼-- · 2019-01-02 17:22

Let me know if you have trouble implementing this. It uses processing.js and has features for changing colors and making the draw point larger and smaller.

<html>
<head>
<!--script librarires-->
<script type="text/javascript" src="processing.js"></script>
<script type="text/javascript" src="init.js"></script>

<!--styles -->
<style type="text/css" src="stylesheet.css">
</style> 
</head>
<body>
<!--toolbox -->
<div id="draggable toolbox"></div>
<script type="application/processing">
// new script
int prevx, prevy;
int newx, newy;
boolean cliked;
color c1 = #000000;
int largeur=2;
int ps = 20;
int px = 50;
int py = 50;

void setup() {
size(500,500);
frameRate(25);
background(50);

 prevx = mouseX;
 prevy = mouseY;
 cliked = false;
 }

void draw() {
 //couleur
 noStroke(0);
 fill(#FFFFFF);//blanc
rect(px, py, ps, ps);
 fill(#000000);
 rect(px, py+(ps), ps, ps);
 fill(#FF0000);
 rect(px, py+(ps*2), ps, ps);
 fill(#00FF00);
 rect(px, py+(ps*3), ps, ps);
 fill(#FFFF00);
 rect(px, py+(ps*4), ps, ps);
 fill(#0000FF);
 rect(px, py+(ps*5), ps, ps);
 //largeur
 fill(#FFFFFF);
 rect(px, py+(ps*7), ps, ps);
  fill(#FFFFFF);
 rect(px, py+(ps*8), ps, ps);
 stroke(#000000);
 line(px+2, py+(ps*7)+(ps/2), px+(ps-2), py+(ps*7)+(ps/2));
 line(px+(ps/2), py+(ps*7)+1, px+(ps/2), py+(ps*8)-1);
 line(px+2, py+(ps*8)+(ps/2), px+(ps-2), py+(ps*8)+(ps/2));

 if(cliked==false){
  prevx = mouseX;
 prevy = mouseY;  
 }
 if(mousePressed) { 
  cliked = true;
 newx = mouseX;
  newy = mouseY;
  strokeWeight(largeur);
  stroke(c1);
  line(prevx, prevy, newx, newy);
  prevx = newx;
 prevy = newy;
 }else{
  cliked= false;
  }
}
void mouseClicked() {
 if (mouseX>=px && mouseX<=(px+ps)){
  //couleur
  if (mouseY>=py && mouseY<=py+(ps*6)){ 
   c1 = get(mouseX, mouseY);
  }
   //largeur
  if (mouseY>=py+(ps*7) && mouseY<=py+(ps*8)){ 
   largeur += 2;
  }
 if (mouseY>=py+(ps*8) && mouseY<=py+(ps*9)){ 
   if (largeur>2){
    largeur -= 2;
   }
  }
 }
}
</script><canvas></canvas>
</body>
</html>

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泛滥B

5楼-- · 2019-01-02 17:24

check this http://jsfiddle.net/ArtBIT/kneDX/. This should direct you on the right direction

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素衣白纱

6楼-- · 2019-01-02 17:31

I had to provide a simple example for this subject so I'll share here:

http://jsfiddle.net/Haelle/v6tfp2e1

class SignTool {
  constructor() {
    this.initVars()
    this.initEvents()
  }

  initVars() {
    this.canvas = $('#canvas')[0]
    this.ctx = this.canvas.getContext("2d")
    this.isMouseClicked = false
    this.isMouseInCanvas = false
    this.prevX = 0
    this.currX = 0
    this.prevY = 0
    this.currY = 0
  }

  initEvents() {
    $('#canvas').on("mousemove", (e) => this.onMouseMove(e))
    $('#canvas').on("mousedown", (e) => this.onMouseDown(e))
    $('#canvas').on("mouseup", () => this.onMouseUp())
    $('#canvas').on("mouseout", () => this.onMouseOut())
    $('#canvas').on("mouseenter", (e) => this.onMouseEnter(e))
  }
  
  onMouseDown(e) {
  	this.isMouseClicked = true
    this.updateCurrentPosition(e)
  }
  
  onMouseUp() {
  	this.isMouseClicked = false
  }
  
  onMouseEnter(e) {
  	this.isMouseInCanvas = true
    this.updateCurrentPosition(e)
  }
  
  onMouseOut() {
  	this.isMouseInCanvas = false
  }

  onMouseMove(e) {
    if (this.isMouseClicked && this.isMouseInCanvas) {
    	this.updateCurrentPosition(e)
      this.draw()
    }
  }
  
  updateCurrentPosition(e) {
      this.prevX = this.currX
      this.prevY = this.currY
      this.currX = e.clientX - this.canvas.offsetLeft
      this.currY = e.clientY - this.canvas.offsetTop
  }
  
  draw() {
    this.ctx.beginPath()
    this.ctx.moveTo(this.prevX, this.prevY)
    this.ctx.lineTo(this.currX, this.currY)
    this.ctx.strokeStyle = "black"
    this.ctx.lineWidth = 2
    this.ctx.stroke()
    this.ctx.closePath()
  }
}

var canvas = new SignTool()

canvas {
  position: absolute;
  border: 2px solid;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="canvas" width="500" height="300"></canvas>

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Draw on HTML5 Canvas using a mouse

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