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| 1 | +<!doctype html> |
| 2 | +<html> |
| 3 | + <head> |
| 4 | + <meta charset="utf-8"> |
| 5 | + <title>Bobbing 1</title> |
| 6 | + <link rel="stylesheet" href="../include/style.css"> |
| 7 | + <style type="text/css"> |
| 8 | + #canvas { |
| 9 | + background: #fff; |
| 10 | + } |
| 11 | + </style> |
| 12 | + </head> |
| 13 | + <body> |
| 14 | + <header> |
| 15 | + Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a> |
| 16 | + </header> |
| 17 | + <canvas id="canvas" width="400" height="400"></canvas> |
| 18 | + |
| 19 | + <script type="module"> |
| 20 | + import Ball from './classes/ball.js' |
| 21 | + |
| 22 | + window.onload = function () { |
| 23 | + const canvas = document.getElementById('canvas'), |
| 24 | + context = canvas.getContext('2d'), |
| 25 | + {width, height} = canvas, |
| 26 | + centerPointY = height / 2, |
| 27 | + ballA = new Ball(80), |
| 28 | + ballB = new Ball(40), |
| 29 | + bouncing = -1.0; |
| 30 | + |
| 31 | + ballA.mass = 2; |
| 32 | + ballA.x = canvas.width - 200; |
| 33 | + ballA.y = canvas.height - 200; |
| 34 | + ballA.vx = 5; |
| 35 | + ballA.vy = 5; |
| 36 | + |
| 37 | + ballB.mass = 1; |
| 38 | + ballB.x = 100; |
| 39 | + ballB.y = 100; |
| 40 | + ballB.vx = 5; |
| 41 | + ballB.vy = 5; |
| 42 | + |
| 43 | + const minDist = ballA.radius + ballB.radius; |
| 44 | + |
| 45 | + function checkBoundary(ball) { |
| 46 | + const {x, y, radius} = ball; |
| 47 | + |
| 48 | + if (x - radius < 0) { |
| 49 | + ball.x = radius; |
| 50 | + ball.vx *= bouncing; |
| 51 | + } else if (x + radius > width) { |
| 52 | + ball.x = width - radius; |
| 53 | + ball.vx *= bouncing; |
| 54 | + } |
| 55 | + |
| 56 | + if (y - radius < 0) { |
| 57 | + ball.y = radius; |
| 58 | + ball.vy *= bouncing; |
| 59 | + } else if (y + radius > height) { |
| 60 | + ball.y = height - radius; |
| 61 | + ball.vy *= bouncing; |
| 62 | + } |
| 63 | + } |
| 64 | + |
| 65 | + function hitProcess(m0, v0, m1, v1) { |
| 66 | + const totalV = v0 - v1; |
| 67 | + const v0Final = ((m0 - m1) * v0 + 2 * m1 * v1) / |
| 68 | + (m0 + m1); |
| 69 | + const v1Final = v0Final + totalV; |
| 70 | + |
| 71 | + return { |
| 72 | + v0: v0Final, |
| 73 | + v1: v1Final |
| 74 | + } |
| 75 | + } |
| 76 | + |
| 77 | + function rotate(x, y, sin, cos, reverse = false) { |
| 78 | + return { |
| 79 | + x: reverse ? (x * cos + y * sin) : (x * cos - y * sin), |
| 80 | + y: reverse ? (y * cos - y * sin) : (x * cos + y * sin) |
| 81 | + } |
| 82 | + } |
| 83 | + |
| 84 | + function hitDetection(ballA, ballB) { |
| 85 | + // ballB 相对于 ballA旋转 |
| 86 | + const dx = ballB.x - ballA.x, |
| 87 | + dy = ballB.y - ballA.y, |
| 88 | + dist = Math.sqrt(dx * dx + dy * dy); |
| 89 | + |
| 90 | + if (dist >= minDist) { |
| 91 | + return; |
| 92 | + } |
| 93 | + |
| 94 | + let angle = Math.atan2(dy, dx), |
| 95 | + sin = Math.sin(angle), |
| 96 | + cos = Math.cos(angle); |
| 97 | + |
| 98 | + // rotate |
| 99 | + let posA = {x: 0, y: 0}, |
| 100 | + posB = rotate(dx, dy, sin, cos, true), |
| 101 | + vA = rotate(ballA.vx, ballA.vy, sin, cos, true), |
| 102 | + vB = rotate(ballB.vx, ballB.vy, sin, cos, true); |
| 103 | + |
| 104 | + let innerX = minDist - dist; |
| 105 | + |
| 106 | + // make sure hit is just at interface |
| 107 | + if (innerX) { |
| 108 | + console.log('inner hit') |
| 109 | + // vA.x * t + vB.x * t = innerX |
| 110 | + // (vA.x + vB.x) * t = innerX; |
| 111 | + let t = innerX / (Math.abs(vA.x) + Math.abs(vB.x)); |
| 112 | + let sA = Math.abs(vA.x * t), |
| 113 | + sB = Math.abs(vB.x * t); |
| 114 | + |
| 115 | + posA.x -= sA; |
| 116 | + posB.x += sB; |
| 117 | + } |
| 118 | + |
| 119 | + // hit |
| 120 | + let {v0: vAX, v1: vBX} = hitProcess(ballA.mass, vA.x, ballB.mass, vB.x); |
| 121 | + vA.x = vAX; |
| 122 | + vB.x = vBX; |
| 123 | + |
| 124 | + // update position |
| 125 | + posA.x += vA.x; |
| 126 | + posB.x += vB.x; |
| 127 | + |
| 128 | + // rotate position back |
| 129 | + let posAFinal = rotate(posA.x, posA.y, sin, cos), |
| 130 | + posBFinal = rotate(posB.x, posB.y, sin, cos); |
| 131 | + |
| 132 | + // B先于A计算，避免A的值改动导致B计算不正确 |
| 133 | + ballB.x = ballA.x + posBFinal.x; |
| 134 | + ballB.y = ballA.y + posBFinal.y; |
| 135 | + ballA.x = ballA.x + posAFinal.x; |
| 136 | + ballA.y = ballA.y + posAFinal.y; |
| 137 | + |
| 138 | + // rotate velocities back |
| 139 | + let vAFinal = rotate(vA.x, vA.y, sin, cos), |
| 140 | + vBFinal = rotate(vB.x, vB.y, sin, cos); |
| 141 | + |
| 142 | + ballA.vx = vAFinal.x; |
| 143 | + ballA.vy = vAFinal.y; |
| 144 | + ballB.vx = vBFinal.x; |
| 145 | + ballB.vy = vBFinal.y; |
| 146 | + } |
| 147 | + |
| 148 | + (function draw(){ |
| 149 | + window.requestAnimationFrame(draw); |
| 150 | + context.clearRect(0, 0, width, height); |
| 151 | + |
| 152 | + ballA.x += ballA.vx; |
| 153 | + ballA.y += ballA.vy; |
| 154 | + ballB.x += ballB.vx; |
| 155 | + ballB.y += ballB.vy; |
| 156 | + |
| 157 | + hitDetection(ballA, ballB); |
| 158 | + |
| 159 | + checkBoundary(ballA); |
| 160 | + checkBoundary(ballB); |
| 161 | + |
| 162 | + ballA.draw(context); |
| 163 | + ballB.draw(context); |
| 164 | + }()) |
| 165 | + } |
| 166 | + </script> |
| 167 | + </body> |
| 168 | +</html> |
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