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Rewrite within_viewport much more cheaply using getBoundingClientRect.

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(imported from commit b7a4434d426a258f89a276f472e71b04c1997df7)
This commit is contained in:
Jessica McKellar
2013-07-12 14:22:27 -04:00
parent 3ddf0187b9
commit 1acca8edfa
1 changed files with 37 additions and 31 deletions
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66
zephyr/static/js/viewport.js
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@@ -89,48 +89,54 @@ exports.set_message_position = function (message_top, message_height, viewport_i
exports.scrollTop(new_scroll_top);
};
exports.message_is_visible = function (vp, message) {
if (! notifications.window_has_focus()) {
return false;
function in_viewport_or_tall(el, top_of_feed, bottom_of_feed) {
var rect = el.getBoundingClientRect();
return ((rect.top > top_of_feed) && // Message top is in view and
((rect.bottom < bottom_of_feed) || // message is fully in view or
((rect.height > bottom_of_feed - top_of_feed) &&
(rect.top < bottom_of_feed)))); // message is tall.
}
var top = vp.visible_top;
var height = vp.visible_height;
var row = rows.get(message.id, current_msg_list.table_name);
if (row.length === 0) return false;
var row_offset = row.offset();
var row_height = row.height();
// Very tall messages are visible once we've gotten past them
return (row_height > height && row_offset.top > top) || within_viewport(row_offset, row_height);
};
function add_to_visible_messages(candidates, visible_messages,
top_of_feed, bottom_of_feed) {
$.each(candidates, function (idx, row) {
var row_rect = row.getBoundingClientRect();
// Mark very tall messages as read once we've gotten past them
if (in_viewport_or_tall(row, top_of_feed, bottom_of_feed)) {
visible_messages.push(current_msg_list.get(rows.id($(row))));
} else {
return false;
}
});
}
exports.visible_messages = function () {
// Note that when using getBoundingClientRect() we are getting offsets
// relative to the visible window, but when using jQuery's offset() we are
// getting offsets relative to the full scrollable window. You can't try to
// compare heights from these two methods.
var selected = current_msg_list.selected_message();
var vp = viewport.message_viewport_info();
var top = vp.visible_top;
var height = vp.visible_height;
var top_of_feed = $(".navbar-top")[0].getBoundingClientRect().bottom;
var bottom_of_feed = $("#compose")[0].getBoundingClientRect().top;
var height = bottom_of_feed - top_of_feed;
// Being simplistic about this, the smallest message is 30 px high.
var selected_row = rows.get(current_msg_list.selected_id(), current_msg_list.table_name);
var num_neighbors = Math.floor(height / 30);
var candidates = $.merge(selected_row.prevAll("tr.message_row[zid]:lt(" + num_neighbors + ")"),
selected_row.nextAll("tr.message_row[zid]:lt(" + num_neighbors + ")"));
// We do this explicitly without merges and without recalculating
// the feed bounds to keep this computation as cheap as possible.
var visible_messages = [];
var i;
var messages_above_pointer = selected_row.prevAll("tr.message_row[zid]:lt(" + num_neighbors + ")");
var messages_below_pointer = selected_row.nextAll("tr.message_row[zid]:lt(" + num_neighbors + ")");
add_to_visible_messages(selected_row, visible_messages,
top_of_feed, bottom_of_feed);
add_to_visible_messages(messages_above_pointer, visible_messages,
top_of_feed, bottom_of_feed);
add_to_visible_messages(messages_below_pointer, visible_messages,
top_of_feed, bottom_of_feed);
for (i = 0; i<candidates.length; i++) {
var row = $(candidates[i]);
var row_offset = row.offset();
var row_height = row.height();
// Mark very tall messages as read once we've gotten past them
if ((row_height > height && row_offset.top > top) || within_viewport(row_offset, row_height)) {
var message = current_msg_list.get(rows.id(row));
visible_messages.push(message);
}
}
return visible_messages;
};