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Use binary search in getVisibleElements()

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fkaelberer 2014-12-26 17:43:13 +01:00 • committed by fkaelberer
parent a033b4bf3d
commit a78bb6b946
3 changed files with 100 additions and 17 deletions
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78
web/ui_utils.js
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@ -160,13 +160,10 @@ function watchScroll(viewAreaElement, callback) {
var currentY = viewAreaElement.scrollTop;
var lastY = state.lastY;
if (currentY > lastY) {
state.down = true;
} else if (currentY < lastY) {
state.down = false;
if (currentY !== lastY) {
state.down = currentY > lastY;
}
state.lastY = currentY;
// else do nothing and use previous value
callback(state);
});
};
@ -182,6 +179,38 @@ function watchScroll(viewAreaElement, callback) {
return state;
}
/**
* Use binary search to find the index of the first item in a given array which
* passes a given condition. The items are expected to be sorted in the sense
* that if the condition is true for one item in the array, then it is also true
* for all following items.
*
* @returns {Number} Index of the first array element to pass the test,
* or |items.length| if no such element exists.
*/
function binarySearchFirstItem(items, condition) {
var minIndex = 0;
var maxIndex = items.length - 1;
if (items.length === 0 || !condition(items[maxIndex])) {
return items.length;
}
if (condition(items[minIndex])) {
return minIndex;
}
while (minIndex < maxIndex) {
var currentIndex = (minIndex + maxIndex) >> 1;
var currentItem = items[currentIndex];
if (condition(currentItem)) {
maxIndex = currentIndex;
} else {
minIndex = currentIndex + 1;
}
}
return minIndex; /* === maxIndex */
}
/**
* Generic helper to find out what elements are visible within a scroll pane.
*/
@ -189,30 +218,45 @@ function getVisibleElements(scrollEl, views, sortByVisibility) {
var top = scrollEl.scrollTop, bottom = top + scrollEl.clientHeight;
var left = scrollEl.scrollLeft, right = left + scrollEl.clientWidth;
var visible = [], view;
function isElementBottomBelowViewTop(view) {
var element = view.div;
var elementBottom =
element.offsetTop + element.clientTop + element.clientHeight;
return elementBottom > top;
}
var visible = [], view, element;
var currentHeight, viewHeight, hiddenHeight, percentHeight;
var currentWidth, viewWidth;
for (var i = 0, ii = views.length; i < ii; ++i) {
var firstVisibleElementInd = (views.length === 0) ? 0 :
binarySearchFirstItem(views, isElementBottomBelowViewTop);
for (var i = firstVisibleElementInd, ii = views.length; i < ii; i++) {
view = views[i];
currentHeight = view.div.offsetTop + view.div.clientTop;
viewHeight = view.div.clientHeight;
if ((currentHeight + viewHeight) < top) {
continue;
}
element = view.div;
currentHeight = element.offsetTop + element.clientTop;
viewHeight = element.clientHeight;
if (currentHeight > bottom) {
break;
}
currentWidth = view.div.offsetLeft + view.div.clientLeft;
viewWidth = view.div.clientWidth;
if ((currentWidth + viewWidth) < left || currentWidth > right) {
currentWidth = element.offsetLeft + element.clientLeft;
viewWidth = element.clientWidth;
if (currentWidth + viewWidth < left || currentWidth > right) {
continue;
}
hiddenHeight = Math.max(0, top - currentHeight) +
Math.max(0, currentHeight + viewHeight - bottom);
percentHeight = ((viewHeight - hiddenHeight) * 100 / viewHeight) | 0;
visible.push({ id: view.id, x: currentWidth, y: currentHeight,
view: view, percent: percentHeight });
visible.push({
id: view.id,
x: currentWidth,
y: currentHeight,
view: view,
percent: percentHeight
});
}
var first = visible[0];