// prop: cssKey
// valueParts(單位與數值)
function adjustCSS(elem, prop, valueParts, tween) {
debugger;
var adjusted;
var scale = 1;
var maxIterations = 20;
//----------------------------
// 獲取現在的值
var currentValue = tween ?
function () {
return tween.cur();
} :
function () {
return jQuery.css(elem, prop, "");
};
var initial = currentValue();
//----------------------------
// 設定的單位
let unit;
if (valueParts && valueParts[3]) {
unit = valueParts[3];
} else {
unit = (jQuery.cssNumber[prop] ? "" : "px");
}
//----------------------------
// 預設單位
// Starting value computation is required for potential unit mismatches
var initialInUnit = (jQuery.cssNumber[prop] || unit !== "px" && +initial);
if (initialInUnit) {
initialInUnit = rcssNum.exec(jQuery.css(elem, prop));
}
//----------------------------
// 若預設單位與設定單位不同
// 必須進入轉換
if (initialInUnit && initialInUnit[3] !== unit) {
// Trust units reported by jQuery.css
unit = unit || initialInUnit[3];
// Make sure we update the tween properties later on
valueParts = valueParts || [];
// Iteratively approximate from a nonzero starting point
initialInUnit = +initial || 1;
do {
// If previous iteration zeroed out, double until we get *something*.
// Use string for doubling so we don't accidentally see scale as unchanged below
scale = scale || ".5";
// Adjust and apply
initialInUnit = initialInUnit / scale;
jQuery.style(elem, prop, initialInUnit + unit);
// Update scale, tolerating zero or NaN from tween.cur()
// Break the loop if scale is unchanged or perfect, or if we've just had enough.
} while (
(function () {
debugger;
let c_value = currentValue();
let a = scale;
// initial(一開始的值)
// 用目標單位移動後，取比例值，供下次修正
let b = scale = (c_value / initial);
return (a !== b) && (scale !== 1) && --maxIterations;
})()
);
}
//----------------------------
if (valueParts) {
initialInUnit = +initialInUnit || +initial || 0;
// Apply relative offset (+=/-=) if specified
adjusted = valueParts[1] ?
initialInUnit + (valueParts[1] + 1) * valueParts[2] :
+valueParts[2];
if (tween) {
tween.unit = unit;
tween.start = initialInUnit;
tween.end = adjusted;
}
}
return adjusted;
}--------------------------------------------------------------------
