如何使用原始画布的上下文和数据更新克隆的 HTML 画布元素？

Question

我编写了一个脚本，允许用户在 html 5 画布元素上绘制简单的线条。最终目标是让这个绘图平铺并在浏览器的其余部分重复。我已经在页面上获得了一个克隆的画布，但正在努力研究如何在多个画布上同时绘制相同的线条。

我会在下面粘贴我的代码

var size = 40;
var md = false;
var canvas = document.getElementById('canvas');
canvas.addEventListener('mousedown', down);
canvas.addEventListener('mouseup', toggledraw);

canvas.width  = 600;
canvas.height = 600;

canvas.addEventListener('mousemove', move);

function move(evt){

  var mousePos = getMousePos(canvas, evt);
  var posx = mousePos.x;
  var posy = mousePos.y;
  draw(canvas, posx, posy);

  window.posx;


  return mousePos;



};


function down(){
  md = true;
}

function toggledraw(){
  md = false;
}

function getMousePos(canvas, evt){
  var rect = canvas.getBoundingClientRect();
  return{
    x:evt.clientX - rect.left,
    y:evt.clientY - rect.top
  };
};

function draw(canvas, posx, posy){
  var context = canvas.getContext('2d');


  if(md){
    context.fillRect(posx, posy, size, size)
  }

};

cloneCanvas(canvas, window.posx, window.posy, size);

function cloneCanvas(canvas, posx, posy, size,) {
  console.log(posx);


  var newCanvas = document.createElement('canvas');
  var context = newCanvas.getContext('2d');
  newCanvas.className = "newNew";


  newCanvas.width = canvas.width;
  newCanvas.height = canvas.height;
  document.body.appendChild(newCanvas);



  //context.fillRect(posx, posy, size, size)
  context.drawImage(canvas, posx, posy);



  return canvas;
}

Answer 1

我会采取的方法是在主画布上绘制后更新克隆的画布。

根据您当前的代码，我首先要返回克隆的画布而不是旧画布。这样你就有了对它的引用。

 function cloneCanvas(canvas, posx, posy, size,) {
   ...
 //  --> return canvas;
 return newCanvas // Becomes this.
}

接下来，看线：

cloneCanvas(canvas, window.posx, window.posy, size);

我看到您正在使用自己的“posx”和“posy”变量。我会摆脱那些，因为你总是想复制整个画布。 （在这种情况下）。像这样换行

var clone = cloneCanvas(canvas, 0, 0, size);

接下来，我编写了一个小辅助函数来链接两个画布。

function drawFromSource(source, destination) {
  return function() {
    var context = destination.getContext('2d');
    context.clearRect(0, 0, destination.width, destination.height);
    context.drawImage(source, 0, 0);
  }
}

此函数返回一个回调，调用该回调时会将原始画布绘制到克隆的画布上。

你像这样初始化它：

var updateClone = drawFromSource(canvas, clone);

最后但同样重要的是，您必须将新创建的回调添加到绘图函数中。在您绘制到主画布之后。

function draw(canvas, posx, posy) {
  var context = canvas.getContext('2d');
  if (md) {
    context.fillRect(posx, posy, size, size)
    updateClone();
  }

};

瞧！ 这是工作代码的链接，我改变了你的一些代码。

https://jsfiddle.net/30efdvz3/5/

只是为了好玩。平铺版只需更改“numberofTiles”

https://jsfiddle.net/30efdvz3/3/

Answer 2

试试这个代码

在此我创建了一个根据画布注册鼠标事件的函数。并为所有画布调用此函数。

var size = 40;
var md = false;
var canvas1 = document.getElementById('canvas');
registerEvents(canvas1)
function move(evt){
    console.log(evt.target.id);
    var canvas = document.getElementById(evt.target.id);
    var mousePos = getMousePos(canvas, evt);
    var posx = mousePos.x;
    var posy = mousePos.y;
    draw(canvas, posx, posy);
    window.posx;
    return mousePos;
};

function registerEvents(canvas){
    canvas.addEventListener('mousedown', down);
    canvas.addEventListener('mouseup', toggledraw);
    canvas.width  = 600;
    canvas.height = 600;
    canvas.addEventListener('mousemove', move);
}
function down(){
    md = true;
}

function toggledraw(){
    md = false;
}

function getMousePos(canvas, evt){
    var rect = canvas.getBoundingClientRect();
    return{
        x:evt.clientX - rect.left,
        y:evt.clientY - rect.top
    };
};

function draw(canvas, posx, posy){
    var context = canvas.getContext('2d');
    if(md){
        context.fillRect(posx, posy, size, size)
    }
};
cloneCanvas(canvas, window.posx, window.posy, size);
function cloneCanvas(canvas, posx, posy, size,) {
    console.log(posx);
    var newCanvas = document.createElement('canvas');
    var context = newCanvas.getContext('2d');
    var id = "newCanvas";
    newCanvas.className = "newNew";
    newCanvas.id = id;
    newCanvas.width = canvas.width;
    newCanvas.height = canvas.height;
    newCanvas.style.border = "1px solid black";
    document.body.appendChild(newCanvas);
    context.drawImage(canvas, posx, posy);
    registerEvents(document.getElementById(id))
    return canvas;
}

Here is working fiddle

Answer 3

其实你已经很接近了，我只是做了一些改变，达到了你想要的，这里是result。

function cloneCanvas(canvas, posx, posy, size,) {
  var newCanvas = document.createElement('canvas');
  var context = newCanvas.getContext('2d');
  ...
  return context; // this should return the context!
}

还有，

var clonedCanvas = cloneCanvas(canvas, window.posx, window.posy, size);
// after you call the function get the 2d context to variable.

最后的变化是，

function draw(canvas, posx, posy){
  var context = canvas.getContext('2d');
  if(md){
  clonedCanvas.fillRect(posx, posy, size, size); // fillRect to variable that you defined at above,
    context.fillRect(posx, posy, size, size)
  }
};

Jsfiddle 输出；

希望有所帮助，