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Scrollbar.js
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Scrollbar.js
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/**
* @provides javelin-scrollbar
* @requires javelin-install
* javelin-dom
* javelin-stratcom
* javelin-vector
* @javelin
*/
/**
* Provides an aesthetic scrollbar.
*
* This shoves an element's scrollbar under a hidden overflow and draws a
* pretty looking fake one in its place. This makes complex UIs with multiple
* independently scrollable panels less hideous by (a) making the scrollbar
* itself prettier and (b) reclaiming the space occupied by the scrollbar.
*
* Note that on OSX the heavy scrollbars are normally drawn only if you have
* a mouse connected. OSX uses more aesthetic touchpad scrollbars normally,
* which these scrollbars emulate.
*
* This class was initially adapted from "Trackpad Scroll Emulator", by
* Jonathan Nicol. See <https://github.com/jnicol/trackpad-scroll-emulator>.
*/
JX.install('Scrollbar', {
construct: function(frame) {
// Before doing anything, check if the scrollbar control has a measurable
// width. If it doesn't, we're already in an environment with an aesthetic
// scrollbar (like Safari on OSX with no mouse connected, or an iPhone)
// and we don't need to do anything.
if (JX.Scrollbar._getScrollbarControlWidth() === 0) {
return;
}
// Wrap the frame content in a bunch of nodes. The frame itself stays on
// the outside so that any positioning information the node had isn't
// disrupted.
// We put a "viewport" node inside of it, which is what actually scrolls.
// This is the node that gets a scrollbar, but we make the viewport very
// slightly too wide for the frame. That hides the scrollbar underneath
// the edge of the frame.
// We put a "content" node inside of the viewport. This allows us to
// measure the content height so we can resize and offset the scrollbar
// handle properly.
// We move all the actual frame content into the "content" node. So it
// ends up wrapped by the "content" node, then by the "viewport" node,
// and finally by the original "frame" node.
JX.DOM.alterClass(frame, 'jx-scrollbar-frame', true);
var content = JX.$N('div', {className: 'jx-scrollbar-content'});
while (frame.firstChild) {
JX.DOM.appendContent(content, frame.firstChild);
}
var viewport = JX.$N('div', {className: 'jx-scrollbar-viewport'}, content);
JX.DOM.appendContent(frame, viewport);
this._frame = frame;
this._viewport = viewport;
this._content = content;
// The handle is the visible node which you can click and drag.
this._handle = JX.$N('div', {className: 'jx-scrollbar-handle'});
// The bar is the area the handle slides up and down in.
this._bar = JX.$N('div', {className: 'jx-scrollbar-bar'}, this._handle);
JX.DOM.prependContent(frame, this._bar);
JX.DOM.listen(this._handle, 'mousedown', null, JX.bind(this, this._ondrag));
JX.DOM.listen(this._bar, 'mousedown', null, JX.bind(this, this._onjump));
JX.enableDispatch(document.body, 'mouseenter');
// Enabling dispatch for this event on `window` allows us to scroll even
// if the mouse cursor is dragged outside the window in at least some
// browsers (for example, Safari on OSX).
JX.enableDispatch(window, 'mousemove');
JX.DOM.listen(viewport, 'mouseenter', null, JX.bind(this, this._onenter));
JX.DOM.listen(frame, 'scroll', null, JX.bind(this, this._onscroll));
JX.DOM.listen(viewport, 'mouseenter', null, JX.bind(this, this._onenter));
JX.DOM.listen(viewport, 'mouseenter', null, JX.bind(this, this._onenter));
JX.Stratcom.listen('mousemove', null, JX.bind(this, this._onmove));
JX.Stratcom.listen('mouseup', null, JX.bind(this, this._ondrop));
JX.Stratcom.listen('resize', null, JX.bind(this, this._onresize));
this._resizeViewport();
this._resizeBar();
},
statics: {
_controlWidth: null,
/**
* Compute the width of the browser's scrollbar control, in pixels.
*/
_getScrollbarControlWidth: function() {
var self = JX.Scrollbar;
if (self._controlWidth === null) {
var tmp = JX.$N('div', {className: 'jx-scrollbar-test'}, '-');
document.body.appendChild(tmp);
var d1 = JX.Vector.getDim(tmp);
tmp.style.overflowY = 'scroll';
var d2 = JX.Vector.getDim(tmp);
JX.DOM.remove(tmp);
self._controlWidth = (d2.x - d1.x);
}
return self._controlWidth;
}
},
members: {
_frame: null,
_viewport: null,
_content: null,
_bar: null,
_handle: null,
_timeout: null,
_dragOrigin: null,
_scrollOrigin: null,
/**
* After the user scrolls the page, show the scrollbar to give them
* feedback about their position.
*/
_onscroll: function() {
this._showBar();
},
/**
* When the user mouses over the viewport, show the scrollbar.
*/
_onenter: function() {
this._showBar();
},
/**
* When the user resizes the window, recalculate everything.
*/
_onresize: function() {
this._resizeViewport();
this._resizeBar();
},
/**
* When the user clicks the bar area (but not the handle), jump up or
* down a page.
*/
_onjump: function(e) {
if (e.getTarget() === this._handle) {
return;
}
var distance = JX.Vector.getDim(this._viewport).y * (7/8);
var epos = JX.$V(e);
var hpos = JX.$V(this._handle);
if (epos.y > hpos.y) {
this._viewport.scrollTop += distance;
} else {
this._viewport.scrollTop -= distance;
}
},
/**
* When the user clicks the scroll handle, begin dragging it.
*/
_ondrag: function(e) {
e.kill();
// Store the position where the drag started.
this._dragOrigin = JX.$V(e);
// Store the original position of the handle.
this._scrollOrigin = this._viewport.scrollTop;
},
/**
* As the user drags the scroll handle up or down, scroll the viewport.
*/
_onmove: function(e) {
if (this._dragOrigin === null) {
return;
}
var p = JX.$V(e);
var offset = (p.y - this._dragOrigin.y);
var ratio = offset / JX.Vector.getDim(this._bar).y;
var adjust = ratio * JX.Vector.getDim(this._content).y;
if (this._shouldSnapback()) {
if (Math.abs(p.x - this._dragOrigin.x) > 140) {
adjust = 0;
}
}
this._viewport.scrollTop = this._scrollOrigin + adjust;
},
/**
* Should the scrollbar snap back to the original position if the user
* drags the mouse away to the left or right, perpendicular to the
* scrollbar?
*
* Scrollbars have this behavior on Windows, but not on OSX or Linux.
*/
_shouldSnapback: function() {
// Since this is an OS-specific behavior, detect the OS. We can't
// reasonably use feature detection here.
return (navigator.platform.indexOf('Win') > -1);
},
/**
* When the user releases the mouse after a drag, stop moving the
* viewport.
*/
_ondrop: function() {
this._dragOrigin = null;
},
/**
* Shove the scrollbar on the viewport under the edge of the frame so the
* user can't see it.
*/
_resizeViewport: function() {
var fdim = JX.Vector.getDim(this._frame);
fdim.x += JX.Scrollbar._getScrollbarControlWidth();
fdim.setDim(this._viewport);
},
/**
* Figure out the correct size and offset of the scrollbar handle.
*/
_resizeBar: function() {
var cdim = JX.Vector.getDim(this._content);
var spos = JX.Vector.getAggregateScrollForNode(this._viewport);
var bdim = JX.Vector.getDim(this._bar);
var ratio = bdim.y / cdim.y;
var offset = Math.round(ratio * spos.y) + 2;
var size = Math.floor(ratio * (bdim.y - 2)) - 2;
if (size < cdim.y) {
this._handle.style.top = offset + 'px';
this._handle.style.height = size + 'px';
JX.DOM.show(this._handle);
} else {
JX.DOM.hide(this._handle);
}
},
/**
* Show the scrollbar for the next second.
*/
_showBar: function() {
this._resizeBar();
JX.DOM.alterClass(this._handle, 'jx-scrollbar-visible', true);
this._clearTimeout();
this._timeout = setTimeout(JX.bind(this, this._hideBar), 1000);
},
/**
* Hide the scrollbar.
*/
_hideBar: function() {
JX.DOM.alterClass(this._handle, 'jx-scrollbar-visible', false);
this._clearTimeout();
},
/**
* Clear the scrollbar hide timeout, if one is set.
*/
_clearTimeout: function() {
if (this._timeout) {
clearTimeout(this._timeout);
this._timeout = null;
}
}
}
});

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