Fix for Multipage selection by dragging mouse in OOP case in PDF.

chrome/browser/resources/pdf/viewport_scroller.js

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+

[Bernhard Bauer, 2015/02/12 09:24:18]

'use strict'; ?

[Deepak, 2015/02/12 10:13:49]

actualy @Sam asked me to remove this earlier.
Anyways adding it again.

[Bernhard Bauer, 2015/02/12 10:31:51]

You mean in
https://codereview.chromium.org/814573004/diff/220001/chrome/browser/resource...
? I thought that was only refering to the extra empty line (there were two of
them).

Sam, is that correct? :)

[Sam McNally, 2015/02/12 22:32:01]

Yes, just the extra empty line.

+/**
+ * @private
+ * The period of time to wait between updating the viewport position by the
+ * scroll velocity.
+ */
+ViewportScroller.DRAG_TIMER_INTERVAL_ = 100;

[Bernhard Bauer, 2015/02/12 09:24:18]

Please add a unit.

[Deepak, 2015/02/12 10:13:49]

Done.

[Bernhard Bauer, 2015/02/12 10:31:51]

Please also add that to the variable name as a prefix (...INTERVAL_MS_). There
is a rule about that somewhere, but I can't find it at the moment.

+
+/**
+ * @private
+ * The maximum drag scroll velocity.
+ */
+ViewportScroller.MAX_DRAG_SCROLL_VELOCITY_ = 100;

[Bernhard Bauer, 2015/02/12 09:24:18]

Please add a unit here as well.

[Deepak, 2015/02/12 10:13:49]

Done.

+
+/**
+ * Creates a new ViewportScroller.
+ * A ViewportScroller scrolls the page in response to drag selection with the
+ * mouse.
+ * @param {Object} viewport The viewport info of the page.
+ * @param {Object} plugin The PDF plugin element.
+ * @param {Object} window The window containing the viewer.
+ */
+function ViewportScroller(viewport, plugin, window) {
+  this.viewport_ = viewport;
+  this.plugin_ = plugin;
+  this.window_ = window;
+  this.mousemoveCallback_ = null;
+  this.timerId_ = null;
+  this.scrollVelocity_ = null;
+}
+
+ViewportScroller.prototype = {
+  /**
+   * @private
+   * Start scrolling the page by |scrollVelocity_| every |DRAG_TIMER_INTERVAL|.
+   */
+  startDragScrollTimer_: function() {
+    if (this.timerId_ === null) {
+      this.timerId_ =
+          this.window_.setInterval(this.dragScrollPage_.bind(this),
+                                   ViewportScroller.DRAG_TIMER_INTERVAL_);
+    }
+  },
+
+  /**
+   * @private
+   * Stops the drag scroll timer if it is active.
+   */
+  stopDragScrollTimer_: function() {
+    if (this.timerId_ !== null) {
+      this.window_.clearInterval(this.timerId_);
+      this.timerId_ = null;
+    }
+  },
+
+  /**
+   * @private
+   * Scrolls the viewport by the current scroll velocity.
+   */
+  dragScrollPage_: function() {
+    var position = this.viewport_.position;
+    position.y += this.scrollVelocity_.y;

[Bernhard Bauer, 2015/02/12 09:24:18]

If the timer doesn't fire after exactly the |DRAG_TIMER_INTERVAL|, the scrolling
might feel a little choppy. Can we adjust this by measuring how much time
actually passed and adjusting the offset accordingly?

[Deepak, 2015/02/12 10:13:49]

I am sorry, I don't understood this comment completely.
Can you please elaborate a little more, or give some reference of usage.
Thanks

[Bernhard Bauer, 2015/02/12 10:31:51]

If we assume we are scrolling at maximum velocity, we want to scroll 100 pixels
every 100ms. If the timer fires after 150ms though (because of timer coalescing,
or the system being busy), we will move 100 pixels in 150ms, which appears
slower. Then if the next timer fires again after 100ms, we will be faster again,
so the overall experience might be choppy. If we adjust the scrolling distance
to (100 pixels * 150ms / 100ms) = 150 pixels, the perceived speed will be always
the same, even if the timer fires a bit earlier or later.

+    position.x += this.scrollVelocity_.x;
+    this.viewport_.position = position;
+  },
+
+  /**
+   * @private
+   * Calculate the velocity to scroll while dragging using the distance of the
+   * cursor outside the viewport.
+   * @param {Object} event The mousemove event.
+   * @return {Object} Object with x and y direction scroll velocity.
+   */
+  calculateVelocity_: function(event) {
+    var x = Math.min(Math.max(-event.offsetX,
+                              event.offsetX - this.plugin_.offsetWidth, 0),
+                     ViewportScroller.MAX_DRAG_SCROLL_VELOCITY_) *
+            Math.sign(event.offsetX);
+    var y = Math.min(Math.max(-event.offsetY,
+                              event.offsetY - this.plugin_.offsetHeight, 0),
+                     ViewportScroller.MAX_DRAG_SCROLL_VELOCITY_) *
+            Math.sign(event.offsetY);
+    return {
+      x: x,
+      y: y
+    };
+  },
+
+  /**
+   * @private
+   * Handles mousemove events. It updates the scroll velocity and starts and
+   * stops timer based on scroll velocity.
+   * @param {Object} event The mousemove event.
+   */
+  onMousemove_: function(event) {
+    this.scrollVelocity_ = this.calculateVelocity_(event);
+    if (!this.scrollVelocity_.x && !this.scrollVelocity_.y)
+      this.stopDragScrollTimer_();
+    else if (!this.timerId_)
+      this.startDragScrollTimer_();
+  },
+
+  /**
+   * Sets whether to scroll the viewport when the mouse is outside the
+   * viewport.
+   * @param {boolean} isSelecting Represents selection status.
+   */
+  setEnableScrolling: function(isSelecting) {
+    if (isSelecting) {
+      if (!this.mousemoveCallback_)
+        this.mousemoveCallback_ = this.onMousemove_.bind(this);
+      this.plugin_.addEventListener('mousemove', this.mousemoveCallback_,
+                                    false);
+    } else {
+      this.stopDragScrollTimer_();
+      if (this.mousemoveCallback_) {
+        this.plugin_.removeEventListener('mousemove', this.mousemoveCallback_,
+                                         false);
+      }
+    }
+  }
+};