canvas简单连线动画的实现代码
这篇文章主要介绍了canvas简单连线动画的实现代码，文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值，需要的朋友们下面随着小编来一起学习学习吧
前言：canvas动画入门系列之简单连线动画。虽然简单，但连线动画应用场景还挺多，因此做了个小demo，一通百通。
step1：绘制点
首先创建个标签<canvas id="canvas"></canvas>
设置几个点的坐标
1 2 3 4 5 6 7 8 9 10 11 12 | const points = [ [200, 100], //上 [300, 200], //右 [100, 200], //左 [200, 100], //上 [200, 300], //下 [100, 200], //左 [300, 200], //右 [200, 300] ]; const canvas = document.querySelector("canvas"); const ctx = canvas.getContext("2d"); |
然后把点给画出来
1 2 3 4 5 6 7 8 9 10 11 12 | points.forEach(([x, y]) => { drawDot(x, y); });function drawDot(x1, y1, r) { ctx.save(); ctx.beginPath(); //不写会和线连起来 ctx.fillStyle = "red"; //绘制成矩形 ctx.arc(x1, y1, r ? r : 2, 0, 2 * Math.PI); ctx.fill(); ctx.restore(); } |
step2：绘制线条
我们封装一个方法,传入起点终点，绘制一根线条
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | function drawLine(x1, y1, x2, y2) { ctx.save(); ctx.beginPath(); //不写每次都会重绘上次的线 ctx.lineCap = "round"; ctx.lineJoin = "round"; var grd = ctx.createLinearGradient(x1, y1, x2, y2); ctx.moveTo(x1, y1); ctx.lineTo(x2, y2); ctx.closePath(); ctx.strokeStyle = "rgba(255,255,255,1)"; ctx.stroke(); ctx.restore(); } |
step3：线条动画
这里面需要计算两点之间的斜率，然后x坐标每次挪动±1单位，已知斜率和x偏移，即可计算出y的偏移。值得注意的是，这个坐标系和数学中的xy坐标系有点不一样，y轴是反的。然后可以引入额外的参数speed控制速度
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | function lineMove(points) { if (points.length < 2) { return; } const [[x1, y1], [x2, y2]] = points; let dx = x2 - x1; let dy = y2 - y1; if (Math.abs(dx) < 1 && Math.abs(dy) < 1) { points = points.slice(1); lineMove(points); return; } let x = x1, y = y1; //线条绘制过程中的终点 if (dx === 0) { (x = x2), (y += (speed * dy) / Math.abs(dy)); } else if (dy === 0) { x += (speed * dx) / Math.abs(dx); y = y2; } else if (Math.abs(dx) >= 1) { let rate = dy / dx; x += (speed * dx) / Math.abs(dx); y += (speed * rate * dx) / Math.abs(dx); } drawLine(x1, y1, x, y); points[0] = [x, y]; window.requestAnimationFrame(function() { lineMove(points); }); } |
主要代码就这么多，先看效果
完整代码
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 | <!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <meta http-equiv="X-UA-Compatible" content="ie=edge" /> <title>canvas-连线动画</title></head><body> <canvas id="canvas" width="400" height="400"></canvas> <script> //起点：10，20 终点：150，200 const points = [ [200, 100], //上 [300, 200], //右 [100, 200], //左 [200, 100], //上 [200, 300], //下 [100, 200], //左 [300, 200], //右 [200, 300] ]; const canvas = document.querySelector("canvas"); const ctx = canvas.getContext("2d"); // const img = new Image(); const speed = 10; //速度 // img.onload = function() { // canvas.width = img.width; // canvas.height = img.height; animate(ctx); // }; // img.src = "./imgs/demo.png"; function animate(ctx) { // ctx.drawImage(img, 0, 0); ctx.fillRect(0, 0, canvas.width, canvas.height); points.forEach(([x, y]) => { drawDot(x, y); }); lineMove(points); } function lineMove(points) { if (points.length < 2) { return; } const [[x1, y1], [x2, y2]] = points; let dx = x2 - x1; let dy = y2 - y1; if (Math.abs(dx) < 1 && Math.abs(dy) < 1) { points = points.slice(1); lineMove(points); return; } let x = x1, y = y1; //线条绘制过程中的终点 if (dx === 0) { (x = x2), (y += (speed * dy) / Math.abs(dy)); } else if (dy === 0) { x += (speed * dx) / Math.abs(dx); y = y2; } else if (Math.abs(dx) >= 1) { let rate = dy / dx; x += (speed * dx) / Math.abs(dx); y += (speed * rate * dx) / Math.abs(dx); } drawLine(x1, y1, x, y); points[0] = [x, y]; window.requestAnimationFrame(function () { lineMove(points); }); } function drawLine(x1, y1, x2, y2) { ctx.save(); ctx.beginPath(); //不写每次都会重绘上次的线 ctx.lineCap = "round"; ctx.lineJoin = "round"; var grd = ctx.createLinearGradient(x1, y1, x2, y2); ctx.moveTo(x1, y1); ctx.lineTo(x2, y2); ctx.closePath(); ctx.strokeStyle = "rgba(255,255,255,1)"; ctx.stroke(); ctx.restore(); } function drawDot(x1, y1, r) { ctx.save(); ctx.beginPath(); //不写会和线连起来 ctx.fillStyle = "red"; //绘制成矩形 ctx.arc(x1, y1, r ? r : 2, 0, 2 * Math.PI); ctx.fill(); ctx.restore(); } </script></body></html> |
以上就是本文的全部内容，希望对大家的学习有所帮助