我想使用画布标签 javascript 绘制一个箭头。我已经使用二次函数做了它，但是我在计算箭头的旋转角度时遇到了问题......
任何人都有这方面的线索？
谢谢
在画布标签上绘制箭头
IT技术
javascript
html5-canvas
drawing
2021-02-25 06:31:01
6个回答
尽可能简单。您必须自己添加 context.beginPath() 并附加 context.stroke() ：
ctx = document.getElementById("c").getContext("2d");
ctx.beginPath();
canvas_arrow(ctx, 10, 30, 200, 150);
canvas_arrow(ctx, 100, 200, 400, 50);
canvas_arrow(ctx, 200, 30, 10, 150);
canvas_arrow(ctx, 400, 200, 100, 50);
ctx.stroke();
function canvas_arrow(context, fromx, fromy, tox, toy) {
var headlen = 10; // length of head in pixels
var dx = tox - fromx;
var dy = toy - fromy;
var angle = Math.atan2(dy, dx);
context.moveTo(fromx, fromy);
context.lineTo(tox, toy);
context.lineTo(tox - headlen * Math.cos(angle - Math.PI / 6), toy - headlen * Math.sin(angle - Math.PI / 6));
context.moveTo(tox, toy);
context.lineTo(tox - headlen * Math.cos(angle + Math.PI / 6), toy - headlen * Math.sin(angle + Math.PI / 6));
}<html>
<body>
<canvas id="c" width="500" height="500"></canvas>
</body>
好的，所以当我试图自己解决这个问题时，这个页面上的第一个答案对我帮助很大，尽管正如其他人已经说过的那样，如果你的线宽大于 1px，你会得到有趣的形状。其他人建议的修复几乎有效，但在尝试使用更宽的箭头时我仍然遇到一些问题。经过几个小时的尝试，我能够将上述解决方案与我自己的一些修补结合起来，得出以下代码，该代码将绘制您想要的任何厚度的箭头，而不会扭曲箭头形状。
function drawArrow(fromx, fromy, tox, toy){
//variables to be used when creating the arrow
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
const width = 22;
var headlen = 10;
// This makes it so the end of the arrow head is located at tox, toy, don't ask where 1.15 comes from
tox -= Math.cos(angle) * ((width*1.15));
toy -= Math.sin(angle) * ((width*1.15));
var angle = Math.atan2(toy-fromy,tox-fromx);
//starting path of the arrow from the start square to the end square and drawing the stroke
ctx.beginPath();
ctx.moveTo(fromx, fromy);
ctx.lineTo(tox, toy);
ctx.strokeStyle = "#cc0000";
ctx.lineWidth = width;
ctx.stroke();
//starting a new path from the head of the arrow to one of the sides of the point
ctx.beginPath();
ctx.moveTo(tox, toy);
ctx.lineTo(tox-headlen*Math.cos(angle-Math.PI/7),toy-headlen*Math.sin(angle-Math.PI/7));
//path from the side point of the arrow, to the other side point
ctx.lineTo(tox-headlen*Math.cos(angle+Math.PI/7),toy-headlen*Math.sin(angle+Math.PI/7));
//path from the side point back to the tip of the arrow, and then again to the opposite side point
ctx.lineTo(tox, toy);
ctx.lineTo(tox-headlen*Math.cos(angle-Math.PI/7),toy-headlen*Math.sin(angle-Math.PI/7));
//draws the paths created above
ctx.strokeStyle = "#cc0000";
ctx.lineWidth = width;
ctx.stroke();
ctx.fillStyle = "#cc0000";
ctx.fill();
}
现在这是我在我的程序中使用的代码。我发现消除失真问题的关键是继续从箭头尖端到一侧点，另一侧点，回到尖端，再回到第一个侧点，然后做一个充满。这修正了箭头的形状。
希望这可以帮助！
这是绘制箭头的另一种方法。它使用这里的三角形方法：https : //stackoverflow.com/a/8937325/1828637
一个小助手功能。
function canvas_arrow(context, fromx, fromy, tox, toy, r){
var x_center = tox;
var y_center = toy;
var angle;
var x;
var y;
context.beginPath();
angle = Math.atan2(toy-fromy,tox-fromx)
x = r*Math.cos(angle) + x_center;
y = r*Math.sin(angle) + y_center;
context.moveTo(x, y);
angle += (1/3)*(2*Math.PI)
x = r*Math.cos(angle) + x_center;
y = r*Math.sin(angle) + y_center;
context.lineTo(x, y);
angle += (1/3)*(2*Math.PI)
x = r*Math.cos(angle) + x_center;
y = r*Math.sin(angle) + y_center;
context.lineTo(x, y);
context.closePath();
context.fill();
}
这是在一行的开头和结尾绘制箭头的演示。
var can = document.getElementById('c');
var ctx = can.getContext('2d');
ctx.lineWidth = 10;
ctx.strokeStyle = 'steelblue';
ctx.fillStyle = 'steelbllue'; // for the triangle fill
ctx.lineJoin = 'butt';
ctx.beginPath();
ctx.moveTo(50, 50);
ctx.lineTo(150, 150);
ctx.stroke();
canvas_arrow(ctx, 50, 50, 150, 150, 10);
canvas_arrow(ctx, 150, 150, 50, 50, 10);
function canvas_arrow(context, fromx, fromy, tox, toy, r){
var x_center = tox;
var y_center = toy;
var angle;
var x;
var y;
context.beginPath();
angle = Math.atan2(toy-fromy,tox-fromx)
x = r*Math.cos(angle) + x_center;
y = r*Math.sin(angle) + y_center;
context.moveTo(x, y);
angle += (1/3)*(2*Math.PI)
x = r*Math.cos(angle) + x_center;
y = r*Math.sin(angle) + y_center;
context.lineTo(x, y);
angle += (1/3)*(2*Math.PI)
x = r*Math.cos(angle) + x_center;
y = r*Math.sin(angle) + y_center;
context.lineTo(x, y);
context.closePath();
context.fill();
}<canvas id="c" width=300 height=300></canvas>你可以做：
ctx.save();
ctx.translate(xOrigin, yOrigin);
ctx.rotate(angle);
// draw your arrow, with its origin at [0, 0]
ctx.restore();
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
arrow({x: 10, y: 10}, {x: 100, y: 170}, 10);
arrow({x: 40, y: 250}, {x: 10, y: 70}, 5);
function arrow (p1, p2, size) {
var angle = Math.atan2((p2.y - p1.y) , (p2.x - p1.x));
var hyp = Math.sqrt((p2.x - p1.x) * (p2.x - p1.x) + (p2.y - p1.y) * (p2.y - p1.y));
ctx.save();
ctx.translate(p1.x, p1.y);
ctx.rotate(angle);
// line
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(hyp - size, 0);
ctx.stroke();
// triangle
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.lineTo(hyp - size, size);
ctx.lineTo(hyp, 0);
ctx.lineTo(hyp - size, -size);
ctx.fill();
ctx.restore();
}<canvas id = "canvas" width = "300" height = "400"></canvas>