在 ipad 上用手指在 html 中绘图？

Question

我正在尝试用手指在画布元素中书写。它适用于桌面浏览器，但不适用于 ipad。
我也尝试使用 touchstart、touchend、touchmove 事件，但它在 ipad 上不起作用。

var pizarra_canvas
var pizarra_context

function init(){            
    pizarra_canvas = document.getElementById("pizarra");
    pizarra_context = pizarra_canvas.getContext("2d");
    pizarra_context.strokeStyle = "#000";
    pizarra_canvas.addEventListener('mousedown',empezarPintar,false);
    pizarra_canvas.addEventListener('mouseup',terminarPintar,false);
    }   

function empezarPintar(e){
pizarra_context.beginPath();
pizarra_context.moveTo(e.clientX-pizarra_canvas.offsetLeft,e.clientY-pizarra_canvas.offsetTop);
pizarra_canvas.addEventListener('mousemove',pintar,false)
}

function terminarPintar(e){
pizarra_canvas.removeEventListener('mousemove',pintar,false);
}

function pintar(e) {
pizarra_context.lineTo(e.clientX-pizarra_canvas.offsetLeft,e.clientY-pizarra_canvas.offsetTop);
pizarra_context.stroke();
}

Answer 1

您需要取消默认事件（即滚动）。此外，最好在文档上触发 mouseup/touchend，因为如果您离开拖动区域并释放按钮，那么画布不知道它应该停止绘制。

var pizarra_canvas
var pizarra_context

function init(){            
    pizarra_canvas = document.getElementById("pizarra");
    pizarra_context = pizarra_canvas.getContext("2d");
    pizarra_context.strokeStyle = "#000";
    pizarra_canvas.addEventListener('mousedown',empezarPintar,false);
    pizarra_canvas.addEventListener('touchstart',empezarPintar,false);
    document.addEventListener('mouseup',terminarPintar,false);
    document.addEventListener('touchend',terminarPintar,false);
    }   

function empezarPintar(e){
  e.preventDefault();
  pizarra_context.beginPath();
  pizarra_context.moveTo(e.pageX-pizarra_canvas.offsetLeft,e.pageY-pizarra_canvas.offsetTop);
  pizarra_canvas.addEventListener('mousemove',pintar,false)
  pizarra_canvas.addEventListener('touchmove',pintar,false)
}

function terminarPintar(e){
  e.preventDefault();
  pizarra_canvas.removeEventListener('mousemove',pintar,false);
  pizarra_canvas.addEventListener('touchmove',pintar,false)
}

function pintar(e) {
  e.preventDefault();
  pizarra_context.lineTo(e.clientX-pizarra_canvas.offsetLeft,e.clientY-pizarra_canvas.offsetTop);
  pizarra_context.stroke();
}
init();

另外，你的 css 在触控设备上应该有这样的东西：

body, html {
  height: 100%;
  overflow: hidden;
}​