本文實例講述了js+html5實現的自由落體運動效果。分享給大家供大家參考，具體如下：
運行效果截圖如下：
具體代碼如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head> <title>canvas自由落體</title> <script type="text/javascript" > var canvasheight = 500; var canvaswidth = 500; var g = 9.8; var plusV = 0.5; function Block(vo, x, y, width, height, g, context) { var _self = this; _self.vo = vo || 0; _self.x = x; _self.y = y; _self.prevX = x; _self.prevY = y; _self.g = g; _self.height = height; _self.width = width; _self.prevTime = new Date().getTime(); context.fillStyle = "black"; _self.down = function () { var time = (new Date().getTime() - _self.prevTime) / 200, y = _self.vo * time + 1 / 2 * _self.g * time * time + _self.y; //console.log("down:time=" + time + ":y=" + y + ":" + _self.vo); if (y + _self.height >= canvasheight) { _self.g--; _self.vo = _self.g * time; _self.prevTime = new Date().getTime(); _self.up(); } else { context.clearRect(_self.prevX, _self.prevY - 1, _self.prevX + _self.height, _self.prevY + _self.width); context.fillRect(_self.x, y, _self.width, _self.height); _self.prevX = x; _self.prevY = y; setTimeout(function () { _self.down(); }, 30); } } _self.up = function () { var time = (new Date().getTime() - _self.prevTime) / 200, v = _self.vo - _self.g * time, y = canvasheight - _self.height - _self.vo * time + 1 / 2 * _self.g * time * time; //console.log("up:time=" + time + ":v=" + v); if (v <= 0) { _self.vo = 0; _self.y = y; _self.prevTime = new Date().getTime(); if (y + _self.height < canvasheight) { _self.down(); } else { return; } } else { context.clearRect(_self.prevX, _self.prevY - 1, _self.prevX + _self.height , _self.prevY + _self.width); context.fillRect(x, y, _self.width, _self.height); _self.prevX = x; _self.prevY = y; setTimeout(function () { _self.up(); }, 30); } } } window.onload = function () { var canvas = document.getElementById('canvas'); var context = canvas.getContext('2d'); height = canvas.offsetHeight; var block = new Block(0, 100, 0, 20, 20, g, context); block.down(); } </script></head><body><center><canvas id="canvas" width="500" height="500" style="background:#DDDDDD" ></canvas></center><input type="button" value="stop" onclick="stop()" /><input type="button" value="start" onclick="start()" /></body></html>更多關于JavaScript運動相關內容感興趣的讀者可查看本站專題：《JavaScript運動效果與技巧匯總》
希望本文所述對大家JavaScript程序設計有所幫助。
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