Johnqing · April 29, 2014 02:16 · Apr 29, 2014
diff --git a/funParabola.js b/funParabola.js
@@ -0,0 +1,183 @@
+/*!
+ * by zhangxinxu(.com) 2012-12-27
+ * you can visit http://www.zhangxinxu.com/wordpress/?p=3855 to get more infomation
+ * under MIT license
+*/
+var funParabola = function(element, target, options) {
+	/*
+	 * 网页模拟现实需要一个比例尺
+	 * 如果按照1像素就是1米来算，显然不合适，因为页面动不动就几百像素
+	 * 页面上，我们放两个物体，200~800像素之间，我们可以映射为现实世界的2米到8米，也就是100:1
+	 * 不过，本方法没有对此有所体现，因此不必在意
+	*/
+
+	var defaults = {
+		speed: 166.67, // 每帧移动的像素大小，每帧（对于大部分显示屏）大约16~17毫秒
+		curvature: 0.001,  // 实际指焦点到准线的距离，你可以抽象成曲率，这里模拟扔物体的抛物线，因此是开口向下的
+		progress: function() {},
+		complete: function() {}
+	};
+
+	var params = {}; options = options || {};
+
+	for (var key in defaults) {
+		params[key] = options[key] || defaults[key];
+	}
+
+	var exports = {
+		mark: function() { return this; },
+		position: function() { return this; },
+		move: function() { return this; },
+		init: function() { return this; }
+	};
+
+	/* 确定移动的方式 
+	 * IE6-IE8 是margin位移
+	 * IE9+使用transform
+	*/
+	var moveStyle = "margin", testDiv = document.createElement("div");
+	if ("oninput" in testDiv) {
+		["", "ms", "webkit"].forEach(function(prefix) {
+			var transform = prefix + (prefix? "T": "t") + "ransform";
+			if (transform in testDiv.style) {
+				moveStyle = transform;
+			}
+		});		
+	}
+
+	// 根据两点坐标以及曲率确定运动曲线函数（也就是确定a, b的值）
+	/* 公式： y = a*x*x + b*x + c;
+	*/
+	var a = params.curvature, b = 0, c = 0;
+
+	// 是否执行运动的标志量
+	var flagMove = true;
+
+	if (element && target && element.nodeType == 1 && target.nodeType == 1) {
+		var rectElement = {}, rectTarget = {};
+
+		// 移动元素的中心点位置，目标元素的中心点位置
+		var centerElement = {}, centerTarget = {};
+
+		// 目标元素的坐标位置
+		var coordElement = {}, coordTarget = {};
+
+		// 标注当前元素的坐标
+		exports.mark = function() {
+			if (flagMove == false) return this;
+			if (typeof coordElement.x == "undefined") this.position();
+			element.setAttribute("data-center", [coordElement.x, coordElement.y].join());
+			target.setAttribute("data-center", [coordTarget.x, coordTarget.y].join());
+			return this;
+		}
+
+		exports.position = function() {
+			if (flagMove == false) return this;
+
+			var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft,
+				scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
+
+			// 初始位置
+			if (moveStyle == "margin") {
+				element.style.marginLeft = element.style.marginTop = "0px";
+			} else {
+				element.style[moveStyle] = "translate(0, 0)";
+			}
+
+			// 四边缘的坐标
+			rectElement = element.getBoundingClientRect();
+			rectTarget = target.getBoundingClientRect();
+
+			// 移动元素的中心点坐标
+			centerElement = {
+				x: rectElement.left + (rectElement.right - rectElement.left) / 2 + scrollLeft,
+				y: rectElement.top + (rectElement.bottom - rectElement.top) / 2	+ scrollTop
+			};
+
+			// 目标元素的中心点位置
+			centerTarget = {
+				x: rectTarget.left + (rectTarget.right - rectTarget.left) / 2 + scrollLeft,
+				y: rectTarget.top + (rectTarget.bottom - rectTarget.top) / 2 + scrollTop		
+			};
+
+			// 转换成相对坐标位置
+			coordElement = {
+				x: 0,
+				y: 0	
+			};
+			coordTarget = {
+				x: -1 * (centerElement.x - centerTarget.x),
+				y:  -1 * (centerElement.y - centerTarget.y)	
+			};
+
+			/*
+			 * 因为经过(0, 0), 因此c = 0
+			 * 于是：
+			 * y = a * x*x + b*x;
+			 * y1 = a * x1*x1 + b*x1;
+			 * y2 = a * x2*x2 + b*x2;
+			 * 利用第二个坐标：
+			 * b = (y2+ a*x2*x2) / x2
+			*/
+			// 于是
+			b = (coordTarget.y - a * coordTarget.x * coordTarget.x) / coordTarget.x;	
+
+			return this;
+		};		
+
+		// 按照这个曲线运动
+		exports.move = function() {
+			// 如果曲线运动还没有结束，不再执行新的运动
+			if (flagMove == false) return this;
+
+			var startx = 0, rate = coordTarget.x > 0? 1: -1;
+
+			var step = function() {
+				// 切线 y'=2ax+b
+				var tangent = 2 * a * startx + b; // = y / x
+				// y*y + x*x = speed
+				// (tangent * x)^2 + x*x = speed
+				// x = Math.sqr(speed / (tangent * tangent + 1));
+				startx = startx + rate * Math.sqrt(params.speed / (tangent * tangent + 1));
+
+				// 防止过界
+				if ((rate == 1 && startx > coordTarget.x) || (rate == -1 && startx < coordTarget.x)) {
+					startx = coordTarget.x;
+				}
+				var x = startx, y = a * x * x + b * x;
+
+				// 标记当前位置，这里有测试使用的嫌疑，实际使用可以将这一行注释
+				element.setAttribute("data-center", [Math.round(x), Math.round(y)].join());
+
+				// x, y目前是坐标，需要转换成定位的像素值
+				if (moveStyle == "margin") {
+					element.style.marginLeft = x + "px";
+					element.style.marginTop = y + "px";
+				} else {
+					element.style[moveStyle] = "translate("+ [x + "px", y + "px"].join() +")";
+				}
+
+				if (startx !== coordTarget.x) {
+					params.progress(x, y);
+					window.requestAnimationFrame(step);	
+				} else {
+					// 运动结束，回调执行
+					params.complete();
+					flagMove = true;	
+				}
+			};
+			window.requestAnimationFrame(step);
+			flagMove = false;
+
+			return this;
+		};
+
+		// 初始化方法
+		exports.init = function() {
+			this.position().mark().move();
+		};
+	}
+
+	return exports;
+};
+
diff --git a/requestAnimationFrame.js b/requestAnimationFrame.js
@@ -0,0 +1,27 @@
+// requestAnimationFrame 补丁
+(function() {
+    var lastTime = 0;
+    var vendors = ['webkit', 'moz'];
+    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
+        window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
+        window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] ||    // name has changed in Webkit
+                                      window[vendors[x] + 'CancelRequestAnimationFrame'];
+    }
+
+    if (!window.requestAnimationFrame) {
+        window.requestAnimationFrame = function(callback, element) {
+            var currTime = new Date().getTime();
+            var timeToCall = Math.max(0, 16.7 - (currTime - lastTime));
+            var id = window.setTimeout(function() {
+                callback(currTime + timeToCall);
+            }, timeToCall);
+            lastTime = currTime + timeToCall;
+            return id;
+        };
+    }
+    if (!window.cancelAnimationFrame) {
+        window.cancelAnimationFrame = function(id) {
+            clearTimeout(id);
+        };
+    }
+}());
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