本文详解如何使用JavaScript在Canvas中绘制两点间的贝塞尔曲线，并在终点绘制矩形与居中文字。核心内容包含箭头方向的计算与绘制逻辑，提供完整的HTML、CSS及JS代码示例，实现从起点到终点的可视化连接效果。
使用JavaScript结合Canvas API，可以在画布上绘制连接两点的曲线，并在曲线终点处绘制矩形框及居中对齐的文字。同时，实现了在连接线上添加箭头的功能，具体视觉效果如图所示：
一、HTML结构代码
具体实现代码如下：
<canvas id="canvas" width="1000" height="600"></canvas>
二、CSS样式代码
canvas {
display: block;
width: 1000px;
height: 600px;
background: conic-gradient(#eee 25%, white 0deg 50%, #eee 0deg 75%, white 0deg) 0 / 20px 20px;
margin-inline: auto;
}
@media (max-width: 640px) {
canvas {
width: 100vw;
height: 60vw;
}
}
三、JavaScript逻辑代码
具体实现代码如下：
var context = document.getElementById("canvas").getContext("2d"); ;
// 绘制尺寸
var width = canvas.width;
var height = canvas.height;
// 两个方块的坐标、尺寸，颜色等数据
var data = [{
x: 800,
y: 180,
width: 200,
height: 50,
color: 'deepskyblue',
text:"+u+ate"
}, {
x: 600,
y: 680,
width: 200,
height: 50,
color: 'deeppink',
text:"gress 迈步"
}];
// 绘制矩形方法
var drawRect = function () {
data.forEach(function (obj) {
context.beginPath();
context.fillStyle = obj.color;
context.fillRect(obj.x, obj.y, obj.width, obj.height);
context.closePath();
context.font="30px Verdana";
context.fillStyle="#fff";
console.log(context.measureText(obj.text))
const textMetrics = context.measureText(obj.text);
// 所有字在这个字体下的高度
let fontHeight = textMetrics.fontBoundingBoxAscent + textMetrics.fontBoundingBoxDescent;
console.log(fontHeight)
context.fillText(obj.text,0,0)
context.fillText(obj.text,obj.x+(obj.width-context.measureText(obj.text).width)/2,obj.y+fontHeight);
});
};
// 绘制连接曲线方法
var drawCurve = function () {
// 按照坐标位置排序
var dataSort = data.sort(function (objA, objB) {
return (objA.y + objA.height) - (objB.y + objB.height);
});
// 知道上下数据
var from = dataSort[0];
var to = dataSort[1];
// 曲线的起点终点
var fromX = from.x + from.width / 2;
var fromY = from.y + from.height;
var toX = to.x + to.width / 2;
var toY = to.y;
// 曲线控制点坐标
var cp1x = fromX;
var cp1y = fromY + (toY - fromY) / 2;
var cp2x = toX;
var cp2y = toY - (toY - fromY) / 2;
// 开始绘制曲线
context.beginPath();
context.lineWidth = 1
context.strokeStyle = '#000';
context.moveTo(fromX, fromY);
// 绘制曲线点
context.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, toX, toY);
context.stroke();
};
// 绘制方法
var draw = function () {
context.clearRect(0, 0, width, height);
drawRect();
drawCurve();
};
draw();
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));
}
至此，核心代码部分已展示完毕。
完整可运行代码
<!DOCTYPE HTML>
<html>
<head>
<style>
canvas {
display: block;
width: 1000px;
height: 600px;
background: conic-gradient(#eee 25%, white 0deg 50%, #eee 0deg 75%, white 0deg) 0 / 20px 20px;
margin-inline: auto;
}
@media (max-width: 640px) {
canvas {
width: 100vw;
height: 60vw;
}
}
</style>
</head>
<body>
<canvas id="canvas" width="2000" height="1200"></canvas>
<script>
var context = document.getElementById("canvas").getContext("2d"); ;
// 绘制尺寸
var width = canvas.width;
var height = canvas.height;
// 两个方块的坐标、尺寸，颜色等数据
var data = [{
x: 800,
y: 180,
width: 200,
height: 50,
color: 'deepskyblue',
text:"+u+ate"
}, {
x: 600,
y: 680,
width: 200,
height: 50,
color: 'deeppink',
text:"gress 迈步"
}];
// 绘制矩形方法
var drawRect = function () {
data.forEach(function (obj) {
context.beginPath();
context.fillStyle = obj.color;
context.fillRect(obj.x, obj.y, obj.width, obj.height);
context.closePath();
context.font="30px Verdana";
context.fillStyle="#fff";
console.log(context.measureText(obj.text))
const textMetrics = context.measureText(obj.text);
// 所有字在这个字体下的高度
let fontHeight = textMetrics.fontBoundingBoxAscent + textMetrics.fontBoundingBoxDescent;
console.log(fontHeight)
context.fillText(obj.text,0,0)
context.fillText(obj.text,obj.x+(obj.width-context.measureText(obj.text).width)/2,obj.y+fontHeight);
});
};
// 绘制连接曲线方法
var drawCurve = function () {
// 按照坐标位置排序
var dataSort = data.sort(function (objA, objB) {
return (objA.y + objA.height) - (objB.y + objB.height);
});
// 知道上下数据
var from = dataSort[0];
var to = dataSort[1];
// 曲线的起点终点
var fromX = from.x + from.width / 2;
var fromY = from.y + from.height;
var toX = to.x + to.width / 2;
var toY = to.y;
// 曲线控制点坐标
var cp1x = fromX;
var cp1y = fromY + (toY - fromY) / 2;
var cp2x = toX;
var cp2y = toY - (toY - fromY) / 2;
// 开始绘制曲线
context.beginPath();
context.lineWidth = 1
context.strokeStyle = '#000';
context.moveTo(fromX, fromY);
// 绘制曲线点
context.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, toX, toY);
context.stroke();
};
// 绘制方法
var draw = function () {
context.clearRect(0, 0, width, height);
drawRect();
drawCurve();
};
draw();
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));
}
</script>
</body>
</html>
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