Question

我正在网页上制作绘图/画布应用程序。我想通过按钮更改颜色，但变量不会更新颜色。我调试了代码，发现它确实更新了，但在画布上绘图时颜色本身没有改变。

HTML：

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

<button onClick="changecolour('blue')">Blue</button>
<button onClick="test()">DEBUG</button>

JavaScript的：

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};

canvas.addEventListener('mousemove', function(e) {
  mouse.x = e.pageX - this.offsetLeft;
  mouse.y = e.pageY - this.offsetTop;
}, false);

var colour = "black";
function changecolour(choice){
    colour = choice;    
}

function test(click){
    alert("You choose " + colour);
}

ctx.lineWidth = 5;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = colour;

canvas.addEventListener('mousedown', function(e) {
    ctx.beginPath();
    ctx.moveTo(mouse.x, mouse.y);

    canvas.addEventListener('mousemove', onPaint, false);
}, false);

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

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

Answer 1

您需要再次更改变量strokeStyle。

function changecolour(choice){
    colour = choice;
    ctx.strokeStyle = colour;
}

Answer 2

您应该影响ctx.strokeStyle本身。当您第一次设置其值时，color ='black'，这意味着您将其设置为黑色。即使您更改“颜色”值，它也会保持黑色。所以在这种情况下，你只需要这样做：

function changecolour(choice){
    ctx.strokeStyle = choice;
}

希望有所帮助

在HTML中单击按钮时JS变量不更新

2 个答案: